Version:  2.0.40 2.2.26 2.4.37 3.8 3.9 3.10 3.11 3.12 3.13 3.14 3.15 3.16 3.17 3.18 3.19 4.0 4.1 4.2 4.3 4.4 4.5

Linux/lib/Kconfig.debug

  1 menu "printk and dmesg options"
  2 
  3 config PRINTK_TIME
  4         bool "Show timing information on printks"
  5         depends on PRINTK
  6         help
  7           Selecting this option causes time stamps of the printk()
  8           messages to be added to the output of the syslog() system
  9           call and at the console.
 10 
 11           The timestamp is always recorded internally, and exported
 12           to /dev/kmsg. This flag just specifies if the timestamp should
 13           be included, not that the timestamp is recorded.
 14 
 15           The behavior is also controlled by the kernel command line
 16           parameter printk.time=1. See Documentation/kernel-parameters.txt
 17 
 18 config MESSAGE_LOGLEVEL_DEFAULT
 19         int "Default message log level (1-7)"
 20         range 1 7
 21         default "4"
 22         help
 23           Default log level for printk statements with no specified priority.
 24 
 25           This was hard-coded to KERN_WARNING since at least 2.6.10 but folks
 26           that are auditing their logs closely may want to set it to a lower
 27           priority.
 28 
 29 config BOOT_PRINTK_DELAY
 30         bool "Delay each boot printk message by N milliseconds"
 31         depends on DEBUG_KERNEL && PRINTK && GENERIC_CALIBRATE_DELAY
 32         help
 33           This build option allows you to read kernel boot messages
 34           by inserting a short delay after each one.  The delay is
 35           specified in milliseconds on the kernel command line,
 36           using "boot_delay=N".
 37 
 38           It is likely that you would also need to use "lpj=M" to preset
 39           the "loops per jiffie" value.
 40           See a previous boot log for the "lpj" value to use for your
 41           system, and then set "lpj=M" before setting "boot_delay=N".
 42           NOTE:  Using this option may adversely affect SMP systems.
 43           I.e., processors other than the first one may not boot up.
 44           BOOT_PRINTK_DELAY also may cause LOCKUP_DETECTOR to detect
 45           what it believes to be lockup conditions.
 46 
 47 config DYNAMIC_DEBUG
 48         bool "Enable dynamic printk() support"
 49         default n
 50         depends on PRINTK
 51         depends on DEBUG_FS
 52         help
 53 
 54           Compiles debug level messages into the kernel, which would not
 55           otherwise be available at runtime. These messages can then be
 56           enabled/disabled based on various levels of scope - per source file,
 57           function, module, format string, and line number. This mechanism
 58           implicitly compiles in all pr_debug() and dev_dbg() calls, which
 59           enlarges the kernel text size by about 2%.
 60 
 61           If a source file is compiled with DEBUG flag set, any
 62           pr_debug() calls in it are enabled by default, but can be
 63           disabled at runtime as below.  Note that DEBUG flag is
 64           turned on by many CONFIG_*DEBUG* options.
 65 
 66           Usage:
 67 
 68           Dynamic debugging is controlled via the 'dynamic_debug/control' file,
 69           which is contained in the 'debugfs' filesystem. Thus, the debugfs
 70           filesystem must first be mounted before making use of this feature.
 71           We refer the control file as: <debugfs>/dynamic_debug/control. This
 72           file contains a list of the debug statements that can be enabled. The
 73           format for each line of the file is:
 74 
 75                 filename:lineno [module]function flags format
 76 
 77           filename : source file of the debug statement
 78           lineno : line number of the debug statement
 79           module : module that contains the debug statement
 80           function : function that contains the debug statement
 81           flags : '=p' means the line is turned 'on' for printing
 82           format : the format used for the debug statement
 83 
 84           From a live system:
 85 
 86                 nullarbor:~ # cat <debugfs>/dynamic_debug/control
 87                 # filename:lineno [module]function flags format
 88                 fs/aio.c:222 [aio]__put_ioctx =_ "__put_ioctx:\040freeing\040%p\012"
 89                 fs/aio.c:248 [aio]ioctx_alloc =_ "ENOMEM:\040nr_events\040too\040high\012"
 90                 fs/aio.c:1770 [aio]sys_io_cancel =_ "calling\040cancel\012"
 91 
 92           Example usage:
 93 
 94                 // enable the message at line 1603 of file svcsock.c
 95                 nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' >
 96                                                 <debugfs>/dynamic_debug/control
 97 
 98                 // enable all the messages in file svcsock.c
 99                 nullarbor:~ # echo -n 'file svcsock.c +p' >
100                                                 <debugfs>/dynamic_debug/control
101 
102                 // enable all the messages in the NFS server module
103                 nullarbor:~ # echo -n 'module nfsd +p' >
104                                                 <debugfs>/dynamic_debug/control
105 
106                 // enable all 12 messages in the function svc_process()
107                 nullarbor:~ # echo -n 'func svc_process +p' >
108                                                 <debugfs>/dynamic_debug/control
109 
110                 // disable all 12 messages in the function svc_process()
111                 nullarbor:~ # echo -n 'func svc_process -p' >
112                                                 <debugfs>/dynamic_debug/control
113 
114           See Documentation/dynamic-debug-howto.txt for additional information.
115 
116 endmenu # "printk and dmesg options"
117 
118 menu "Compile-time checks and compiler options"
119 
120 config DEBUG_INFO
121         bool "Compile the kernel with debug info"
122         depends on DEBUG_KERNEL && !COMPILE_TEST
123         help
124           If you say Y here the resulting kernel image will include
125           debugging info resulting in a larger kernel image.
126           This adds debug symbols to the kernel and modules (gcc -g), and
127           is needed if you intend to use kernel crashdump or binary object
128           tools like crash, kgdb, LKCD, gdb, etc on the kernel.
129           Say Y here only if you plan to debug the kernel.
130 
131           If unsure, say N.
132 
133 config DEBUG_INFO_REDUCED
134         bool "Reduce debugging information"
135         depends on DEBUG_INFO
136         help
137           If you say Y here gcc is instructed to generate less debugging
138           information for structure types. This means that tools that
139           need full debugging information (like kgdb or systemtap) won't
140           be happy. But if you merely need debugging information to
141           resolve line numbers there is no loss. Advantage is that
142           build directory object sizes shrink dramatically over a full
143           DEBUG_INFO build and compile times are reduced too.
144           Only works with newer gcc versions.
145 
146 config DEBUG_INFO_SPLIT
147         bool "Produce split debuginfo in .dwo files"
148         depends on DEBUG_INFO
149         help
150           Generate debug info into separate .dwo files. This significantly
151           reduces the build directory size for builds with DEBUG_INFO,
152           because it stores the information only once on disk in .dwo
153           files instead of multiple times in object files and executables.
154           In addition the debug information is also compressed.
155 
156           Requires recent gcc (4.7+) and recent gdb/binutils.
157           Any tool that packages or reads debug information would need
158           to know about the .dwo files and include them.
159           Incompatible with older versions of ccache.
160 
161 config DEBUG_INFO_DWARF4
162         bool "Generate dwarf4 debuginfo"
163         depends on DEBUG_INFO
164         help
165           Generate dwarf4 debug info. This requires recent versions
166           of gcc and gdb. It makes the debug information larger.
167           But it significantly improves the success of resolving
168           variables in gdb on optimized code.
169 
170 config GDB_SCRIPTS
171         bool "Provide GDB scripts for kernel debugging"
172         depends on DEBUG_INFO
173         help
174           This creates the required links to GDB helper scripts in the
175           build directory. If you load vmlinux into gdb, the helper
176           scripts will be automatically imported by gdb as well, and
177           additional functions are available to analyze a Linux kernel
178           instance. See Documentation/gdb-kernel-debugging.txt for further
179           details.
180 
181 config ENABLE_WARN_DEPRECATED
182         bool "Enable __deprecated logic"
183         default y
184         help
185           Enable the __deprecated logic in the kernel build.
186           Disable this to suppress the "warning: 'foo' is deprecated
187           (declared at kernel/power/somefile.c:1234)" messages.
188 
189 config ENABLE_MUST_CHECK
190         bool "Enable __must_check logic"
191         default y
192         help
193           Enable the __must_check logic in the kernel build.  Disable this to
194           suppress the "warning: ignoring return value of 'foo', declared with
195           attribute warn_unused_result" messages.
196 
197 config FRAME_WARN
198         int "Warn for stack frames larger than (needs gcc 4.4)"
199         range 0 8192
200         default 0 if KASAN
201         default 1024 if !64BIT
202         default 2048 if 64BIT
203         help
204           Tell gcc to warn at build time for stack frames larger than this.
205           Setting this too low will cause a lot of warnings.
206           Setting it to 0 disables the warning.
207           Requires gcc 4.4
208 
209 config STRIP_ASM_SYMS
210         bool "Strip assembler-generated symbols during link"
211         default n
212         help
213           Strip internal assembler-generated symbols during a link (symbols
214           that look like '.Lxxx') so they don't pollute the output of
215           get_wchan() and suchlike.
216 
217 config READABLE_ASM
218         bool "Generate readable assembler code"
219         depends on DEBUG_KERNEL
220         help
221           Disable some compiler optimizations that tend to generate human unreadable
222           assembler output. This may make the kernel slightly slower, but it helps
223           to keep kernel developers who have to stare a lot at assembler listings
224           sane.
225 
226 config UNUSED_SYMBOLS
227         bool "Enable unused/obsolete exported symbols"
228         default y if X86
229         help
230           Unused but exported symbols make the kernel needlessly bigger.  For
231           that reason most of these unused exports will soon be removed.  This
232           option is provided temporarily to provide a transition period in case
233           some external kernel module needs one of these symbols anyway. If you
234           encounter such a case in your module, consider if you are actually
235           using the right API.  (rationale: since nobody in the kernel is using
236           this in a module, there is a pretty good chance it's actually the
237           wrong interface to use).  If you really need the symbol, please send a
238           mail to the linux kernel mailing list mentioning the symbol and why
239           you really need it, and what the merge plan to the mainline kernel for
240           your module is.
241 
242 config PAGE_OWNER
243         bool "Track page owner"
244         depends on DEBUG_KERNEL && STACKTRACE_SUPPORT
245         select DEBUG_FS
246         select STACKTRACE
247         select PAGE_EXTENSION
248         help
249           This keeps track of what call chain is the owner of a page, may
250           help to find bare alloc_page(s) leaks. Even if you include this
251           feature on your build, it is disabled in default. You should pass
252           "page_owner=on" to boot parameter in order to enable it. Eats
253           a fair amount of memory if enabled. See tools/vm/page_owner_sort.c
254           for user-space helper.
255 
256           If unsure, say N.
257 
258 config DEBUG_FS
259         bool "Debug Filesystem"
260         help
261           debugfs is a virtual file system that kernel developers use to put
262           debugging files into.  Enable this option to be able to read and
263           write to these files.
264 
265           For detailed documentation on the debugfs API, see
266           Documentation/DocBook/filesystems.
267 
268           If unsure, say N.
269 
270 config HEADERS_CHECK
271         bool "Run 'make headers_check' when building vmlinux"
272         depends on !UML
273         help
274           This option will extract the user-visible kernel headers whenever
275           building the kernel, and will run basic sanity checks on them to
276           ensure that exported files do not attempt to include files which
277           were not exported, etc.
278 
279           If you're making modifications to header files which are
280           relevant for userspace, say 'Y', and check the headers
281           exported to $(INSTALL_HDR_PATH) (usually 'usr/include' in
282           your build tree), to make sure they're suitable.
283 
284 config DEBUG_SECTION_MISMATCH
285         bool "Enable full Section mismatch analysis"
286         help
287           The section mismatch analysis checks if there are illegal
288           references from one section to another section.
289           During linktime or runtime, some sections are dropped;
290           any use of code/data previously in these sections would
291           most likely result in an oops.
292           In the code, functions and variables are annotated with
293           __init,, etc. (see the full list in include/linux/init.h),
294           which results in the code/data being placed in specific sections.
295           The section mismatch analysis is always performed after a full
296           kernel build, and enabling this option causes the following
297           additional steps to occur:
298           - Add the option -fno-inline-functions-called-once to gcc commands.
299             When inlining a function annotated with __init in a non-init
300             function, we would lose the section information and thus
301             the analysis would not catch the illegal reference.
302             This option tells gcc to inline less (but it does result in
303             a larger kernel).
304           - Run the section mismatch analysis for each module/built-in.o file.
305             When we run the section mismatch analysis on vmlinux.o, we
306             lose valueble information about where the mismatch was
307             introduced.
308             Running the analysis for each module/built-in.o file
309             tells where the mismatch happens much closer to the
310             source. The drawback is that the same mismatch is
311             reported at least twice.
312           - Enable verbose reporting from modpost in order to help resolve
313             the section mismatches that are reported.
314 
315 config SECTION_MISMATCH_WARN_ONLY
316         bool "Make section mismatch errors non-fatal"
317         default y
318         help
319           If you say N here, the build process will fail if there are any
320           section mismatch, instead of just throwing warnings.
321 
322           If unsure, say Y.
323 
324 #
325 # Select this config option from the architecture Kconfig, if it
326 # is preferred to always offer frame pointers as a config
327 # option on the architecture (regardless of KERNEL_DEBUG):
328 #
329 config ARCH_WANT_FRAME_POINTERS
330         bool
331         help
332 
333 config FRAME_POINTER
334         bool "Compile the kernel with frame pointers"
335         depends on DEBUG_KERNEL && \
336                 (CRIS || M68K || FRV || UML || \
337                  AVR32 || SUPERH || BLACKFIN || MN10300 || METAG) || \
338                 ARCH_WANT_FRAME_POINTERS
339         default y if (DEBUG_INFO && UML) || ARCH_WANT_FRAME_POINTERS
340         help
341           If you say Y here the resulting kernel image will be slightly
342           larger and slower, but it gives very useful debugging information
343           in case of kernel bugs. (precise oopses/stacktraces/warnings)
344 
345 config DEBUG_FORCE_WEAK_PER_CPU
346         bool "Force weak per-cpu definitions"
347         depends on DEBUG_KERNEL
348         help
349           s390 and alpha require percpu variables in modules to be
350           defined weak to work around addressing range issue which
351           puts the following two restrictions on percpu variable
352           definitions.
353 
354           1. percpu symbols must be unique whether static or not
355           2. percpu variables can't be defined inside a function
356 
357           To ensure that generic code follows the above rules, this
358           option forces all percpu variables to be defined as weak.
359 
360 endmenu # "Compiler options"
361 
362 config MAGIC_SYSRQ
363         bool "Magic SysRq key"
364         depends on !UML
365         help
366           If you say Y here, you will have some control over the system even
367           if the system crashes for example during kernel debugging (e.g., you
368           will be able to flush the buffer cache to disk, reboot the system
369           immediately or dump some status information). This is accomplished
370           by pressing various keys while holding SysRq (Alt+PrintScreen). It
371           also works on a serial console (on PC hardware at least), if you
372           send a BREAK and then within 5 seconds a command keypress. The
373           keys are documented in <file:Documentation/sysrq.txt>. Don't say Y
374           unless you really know what this hack does.
375 
376 config MAGIC_SYSRQ_DEFAULT_ENABLE
377         hex "Enable magic SysRq key functions by default"
378         depends on MAGIC_SYSRQ
379         default 0x1
380         help
381           Specifies which SysRq key functions are enabled by default.
382           This may be set to 1 or 0 to enable or disable them all, or
383           to a bitmask as described in Documentation/sysrq.txt.
384 
385 config DEBUG_KERNEL
386         bool "Kernel debugging"
387         help
388           Say Y here if you are developing drivers or trying to debug and
389           identify kernel problems.
390 
391 menu "Memory Debugging"
392 
393 source mm/Kconfig.debug
394 
395 config DEBUG_OBJECTS
396         bool "Debug object operations"
397         depends on DEBUG_KERNEL
398         help
399           If you say Y here, additional code will be inserted into the
400           kernel to track the life time of various objects and validate
401           the operations on those objects.
402 
403 config DEBUG_OBJECTS_SELFTEST
404         bool "Debug objects selftest"
405         depends on DEBUG_OBJECTS
406         help
407           This enables the selftest of the object debug code.
408 
409 config DEBUG_OBJECTS_FREE
410         bool "Debug objects in freed memory"
411         depends on DEBUG_OBJECTS
412         help
413           This enables checks whether a k/v free operation frees an area
414           which contains an object which has not been deactivated
415           properly. This can make kmalloc/kfree-intensive workloads
416           much slower.
417 
418 config DEBUG_OBJECTS_TIMERS
419         bool "Debug timer objects"
420         depends on DEBUG_OBJECTS
421         help
422           If you say Y here, additional code will be inserted into the
423           timer routines to track the life time of timer objects and
424           validate the timer operations.
425 
426 config DEBUG_OBJECTS_WORK
427         bool "Debug work objects"
428         depends on DEBUG_OBJECTS
429         help
430           If you say Y here, additional code will be inserted into the
431           work queue routines to track the life time of work objects and
432           validate the work operations.
433 
434 config DEBUG_OBJECTS_RCU_HEAD
435         bool "Debug RCU callbacks objects"
436         depends on DEBUG_OBJECTS
437         help
438           Enable this to turn on debugging of RCU list heads (call_rcu() usage).
439 
440 config DEBUG_OBJECTS_PERCPU_COUNTER
441         bool "Debug percpu counter objects"
442         depends on DEBUG_OBJECTS
443         help
444           If you say Y here, additional code will be inserted into the
445           percpu counter routines to track the life time of percpu counter
446           objects and validate the percpu counter operations.
447 
448 config DEBUG_OBJECTS_ENABLE_DEFAULT
449         int "debug_objects bootup default value (0-1)"
450         range 0 1
451         default "1"
452         depends on DEBUG_OBJECTS
453         help
454           Debug objects boot parameter default value
455 
456 config DEBUG_SLAB
457         bool "Debug slab memory allocations"
458         depends on DEBUG_KERNEL && SLAB && !KMEMCHECK
459         help
460           Say Y here to have the kernel do limited verification on memory
461           allocation as well as poisoning memory on free to catch use of freed
462           memory. This can make kmalloc/kfree-intensive workloads much slower.
463 
464 config DEBUG_SLAB_LEAK
465         bool "Memory leak debugging"
466         depends on DEBUG_SLAB
467 
468 config SLUB_DEBUG_ON
469         bool "SLUB debugging on by default"
470         depends on SLUB && SLUB_DEBUG && !KMEMCHECK
471         default n
472         help
473           Boot with debugging on by default. SLUB boots by default with
474           the runtime debug capabilities switched off. Enabling this is
475           equivalent to specifying the "slub_debug" parameter on boot.
476           There is no support for more fine grained debug control like
477           possible with slub_debug=xxx. SLUB debugging may be switched
478           off in a kernel built with CONFIG_SLUB_DEBUG_ON by specifying
479           "slub_debug=-".
480 
481 config SLUB_STATS
482         default n
483         bool "Enable SLUB performance statistics"
484         depends on SLUB && SYSFS
485         help
486           SLUB statistics are useful to debug SLUBs allocation behavior in
487           order find ways to optimize the allocator. This should never be
488           enabled for production use since keeping statistics slows down
489           the allocator by a few percentage points. The slabinfo command
490           supports the determination of the most active slabs to figure
491           out which slabs are relevant to a particular load.
492           Try running: slabinfo -DA
493 
494 config HAVE_DEBUG_KMEMLEAK
495         bool
496 
497 config DEBUG_KMEMLEAK
498         bool "Kernel memory leak detector"
499         depends on DEBUG_KERNEL && HAVE_DEBUG_KMEMLEAK
500         select DEBUG_FS
501         select STACKTRACE if STACKTRACE_SUPPORT
502         select KALLSYMS
503         select CRC32
504         help
505           Say Y here if you want to enable the memory leak
506           detector. The memory allocation/freeing is traced in a way
507           similar to the Boehm's conservative garbage collector, the
508           difference being that the orphan objects are not freed but
509           only shown in /sys/kernel/debug/kmemleak. Enabling this
510           feature will introduce an overhead to memory
511           allocations. See Documentation/kmemleak.txt for more
512           details.
513 
514           Enabling DEBUG_SLAB or SLUB_DEBUG may increase the chances
515           of finding leaks due to the slab objects poisoning.
516 
517           In order to access the kmemleak file, debugfs needs to be
518           mounted (usually at /sys/kernel/debug).
519 
520 config DEBUG_KMEMLEAK_EARLY_LOG_SIZE
521         int "Maximum kmemleak early log entries"
522         depends on DEBUG_KMEMLEAK
523         range 200 40000
524         default 400
525         help
526           Kmemleak must track all the memory allocations to avoid
527           reporting false positives. Since memory may be allocated or
528           freed before kmemleak is initialised, an early log buffer is
529           used to store these actions. If kmemleak reports "early log
530           buffer exceeded", please increase this value.
531 
532 config DEBUG_KMEMLEAK_TEST
533         tristate "Simple test for the kernel memory leak detector"
534         depends on DEBUG_KMEMLEAK && m
535         help
536           This option enables a module that explicitly leaks memory.
537 
538           If unsure, say N.
539 
540 config DEBUG_KMEMLEAK_DEFAULT_OFF
541         bool "Default kmemleak to off"
542         depends on DEBUG_KMEMLEAK
543         help
544           Say Y here to disable kmemleak by default. It can then be enabled
545           on the command line via kmemleak=on.
546 
547 config DEBUG_STACK_USAGE
548         bool "Stack utilization instrumentation"
549         depends on DEBUG_KERNEL && !IA64 && !PARISC && !METAG
550         help
551           Enables the display of the minimum amount of free stack which each
552           task has ever had available in the sysrq-T and sysrq-P debug output.
553 
554           This option will slow down process creation somewhat.
555 
556 config DEBUG_VM
557         bool "Debug VM"
558         depends on DEBUG_KERNEL
559         help
560           Enable this to turn on extended checks in the virtual-memory system
561           that may impact performance.
562 
563           If unsure, say N.
564 
565 config DEBUG_VM_VMACACHE
566         bool "Debug VMA caching"
567         depends on DEBUG_VM
568         help
569           Enable this to turn on VMA caching debug information. Doing so
570           can cause significant overhead, so only enable it in non-production
571           environments.
572 
573           If unsure, say N.
574 
575 config DEBUG_VM_RB
576         bool "Debug VM red-black trees"
577         depends on DEBUG_VM
578         help
579           Enable VM red-black tree debugging information and extra validations.
580 
581           If unsure, say N.
582 
583 config DEBUG_VM_PGFLAGS
584         bool "Debug page-flags operations"
585         depends on DEBUG_VM
586         help
587           Enables extra validation on page flags operations.
588 
589           If unsure, say N.
590 
591 config DEBUG_VIRTUAL
592         bool "Debug VM translations"
593         depends on DEBUG_KERNEL && X86
594         help
595           Enable some costly sanity checks in virtual to page code. This can
596           catch mistakes with virt_to_page() and friends.
597 
598           If unsure, say N.
599 
600 config DEBUG_NOMMU_REGIONS
601         bool "Debug the global anon/private NOMMU mapping region tree"
602         depends on DEBUG_KERNEL && !MMU
603         help
604           This option causes the global tree of anonymous and private mapping
605           regions to be regularly checked for invalid topology.
606 
607 config DEBUG_MEMORY_INIT
608         bool "Debug memory initialisation" if EXPERT
609         default !EXPERT
610         help
611           Enable this for additional checks during memory initialisation.
612           The sanity checks verify aspects of the VM such as the memory model
613           and other information provided by the architecture. Verbose
614           information will be printed at KERN_DEBUG loglevel depending
615           on the mminit_loglevel= command-line option.
616 
617           If unsure, say Y
618 
619 config MEMORY_NOTIFIER_ERROR_INJECT
620         tristate "Memory hotplug notifier error injection module"
621         depends on MEMORY_HOTPLUG_SPARSE && NOTIFIER_ERROR_INJECTION
622         help
623           This option provides the ability to inject artificial errors to
624           memory hotplug notifier chain callbacks.  It is controlled through
625           debugfs interface under /sys/kernel/debug/notifier-error-inject/memory
626 
627           If the notifier call chain should be failed with some events
628           notified, write the error code to "actions/<notifier event>/error".
629 
630           Example: Inject memory hotplug offline error (-12 == -ENOMEM)
631 
632           # cd /sys/kernel/debug/notifier-error-inject/memory
633           # echo -12 > actions/MEM_GOING_OFFLINE/error
634           # echo offline > /sys/devices/system/memory/memoryXXX/state
635           bash: echo: write error: Cannot allocate memory
636 
637           To compile this code as a module, choose M here: the module will
638           be called memory-notifier-error-inject.
639 
640           If unsure, say N.
641 
642 config DEBUG_PER_CPU_MAPS
643         bool "Debug access to per_cpu maps"
644         depends on DEBUG_KERNEL
645         depends on SMP
646         help
647           Say Y to verify that the per_cpu map being accessed has
648           been set up. This adds a fair amount of code to kernel memory
649           and decreases performance.
650 
651           Say N if unsure.
652 
653 config DEBUG_HIGHMEM
654         bool "Highmem debugging"
655         depends on DEBUG_KERNEL && HIGHMEM
656         help
657           This option enables additional error checking for high memory
658           systems.  Disable for production systems.
659 
660 config HAVE_DEBUG_STACKOVERFLOW
661         bool
662 
663 config DEBUG_STACKOVERFLOW
664         bool "Check for stack overflows"
665         depends on DEBUG_KERNEL && HAVE_DEBUG_STACKOVERFLOW
666         ---help---
667           Say Y here if you want to check for overflows of kernel, IRQ
668           and exception stacks (if your architecture uses them). This
669           option will show detailed messages if free stack space drops
670           below a certain limit.
671 
672           These kinds of bugs usually occur when call-chains in the
673           kernel get too deep, especially when interrupts are
674           involved.
675 
676           Use this in cases where you see apparently random memory
677           corruption, especially if it appears in 'struct thread_info'
678 
679           If in doubt, say "N".
680 
681 source "lib/Kconfig.kmemcheck"
682 
683 source "lib/Kconfig.kasan"
684 
685 endmenu # "Memory Debugging"
686 
687 config DEBUG_SHIRQ
688         bool "Debug shared IRQ handlers"
689         depends on DEBUG_KERNEL
690         help
691           Enable this to generate a spurious interrupt as soon as a shared
692           interrupt handler is registered, and just before one is deregistered.
693           Drivers ought to be able to handle interrupts coming in at those
694           points; some don't and need to be caught.
695 
696 menu "Debug Lockups and Hangs"
697 
698 config LOCKUP_DETECTOR
699         bool "Detect Hard and Soft Lockups"
700         depends on DEBUG_KERNEL && !S390
701         help
702           Say Y here to enable the kernel to act as a watchdog to detect
703           hard and soft lockups.
704 
705           Softlockups are bugs that cause the kernel to loop in kernel
706           mode for more than 20 seconds, without giving other tasks a
707           chance to run.  The current stack trace is displayed upon
708           detection and the system will stay locked up.
709 
710           Hardlockups are bugs that cause the CPU to loop in kernel mode
711           for more than 10 seconds, without letting other interrupts have a
712           chance to run.  The current stack trace is displayed upon detection
713           and the system will stay locked up.
714 
715           The overhead should be minimal.  A periodic hrtimer runs to
716           generate interrupts and kick the watchdog task every 4 seconds.
717           An NMI is generated every 10 seconds or so to check for hardlockups.
718 
719           The frequency of hrtimer and NMI events and the soft and hard lockup
720           thresholds can be controlled through the sysctl watchdog_thresh.
721 
722 config HARDLOCKUP_DETECTOR
723         def_bool y
724         depends on LOCKUP_DETECTOR && !HAVE_NMI_WATCHDOG
725         depends on PERF_EVENTS && HAVE_PERF_EVENTS_NMI
726 
727 config BOOTPARAM_HARDLOCKUP_PANIC
728         bool "Panic (Reboot) On Hard Lockups"
729         depends on HARDLOCKUP_DETECTOR
730         help
731           Say Y here to enable the kernel to panic on "hard lockups",
732           which are bugs that cause the kernel to loop in kernel
733           mode with interrupts disabled for more than 10 seconds (configurable
734           using the watchdog_thresh sysctl).
735 
736           Say N if unsure.
737 
738 config BOOTPARAM_HARDLOCKUP_PANIC_VALUE
739         int
740         depends on HARDLOCKUP_DETECTOR
741         range 0 1
742         default 0 if !BOOTPARAM_HARDLOCKUP_PANIC
743         default 1 if BOOTPARAM_HARDLOCKUP_PANIC
744 
745 config BOOTPARAM_SOFTLOCKUP_PANIC
746         bool "Panic (Reboot) On Soft Lockups"
747         depends on LOCKUP_DETECTOR
748         help
749           Say Y here to enable the kernel to panic on "soft lockups",
750           which are bugs that cause the kernel to loop in kernel
751           mode for more than 20 seconds (configurable using the watchdog_thresh
752           sysctl), without giving other tasks a chance to run.
753 
754           The panic can be used in combination with panic_timeout,
755           to cause the system to reboot automatically after a
756           lockup has been detected. This feature is useful for
757           high-availability systems that have uptime guarantees and
758           where a lockup must be resolved ASAP.
759 
760           Say N if unsure.
761 
762 config BOOTPARAM_SOFTLOCKUP_PANIC_VALUE
763         int
764         depends on LOCKUP_DETECTOR
765         range 0 1
766         default 0 if !BOOTPARAM_SOFTLOCKUP_PANIC
767         default 1 if BOOTPARAM_SOFTLOCKUP_PANIC
768 
769 config DETECT_HUNG_TASK
770         bool "Detect Hung Tasks"
771         depends on DEBUG_KERNEL
772         default LOCKUP_DETECTOR
773         help
774           Say Y here to enable the kernel to detect "hung tasks",
775           which are bugs that cause the task to be stuck in
776           uninterruptible "D" state indefinitiley.
777 
778           When a hung task is detected, the kernel will print the
779           current stack trace (which you should report), but the
780           task will stay in uninterruptible state. If lockdep is
781           enabled then all held locks will also be reported. This
782           feature has negligible overhead.
783 
784 config DEFAULT_HUNG_TASK_TIMEOUT
785         int "Default timeout for hung task detection (in seconds)"
786         depends on DETECT_HUNG_TASK
787         default 120
788         help
789           This option controls the default timeout (in seconds) used
790           to determine when a task has become non-responsive and should
791           be considered hung.
792 
793           It can be adjusted at runtime via the kernel.hung_task_timeout_secs
794           sysctl or by writing a value to
795           /proc/sys/kernel/hung_task_timeout_secs.
796 
797           A timeout of 0 disables the check.  The default is two minutes.
798           Keeping the default should be fine in most cases.
799 
800 config BOOTPARAM_HUNG_TASK_PANIC
801         bool "Panic (Reboot) On Hung Tasks"
802         depends on DETECT_HUNG_TASK
803         help
804           Say Y here to enable the kernel to panic on "hung tasks",
805           which are bugs that cause the kernel to leave a task stuck
806           in uninterruptible "D" state.
807 
808           The panic can be used in combination with panic_timeout,
809           to cause the system to reboot automatically after a
810           hung task has been detected. This feature is useful for
811           high-availability systems that have uptime guarantees and
812           where a hung tasks must be resolved ASAP.
813 
814           Say N if unsure.
815 
816 config BOOTPARAM_HUNG_TASK_PANIC_VALUE
817         int
818         depends on DETECT_HUNG_TASK
819         range 0 1
820         default 0 if !BOOTPARAM_HUNG_TASK_PANIC
821         default 1 if BOOTPARAM_HUNG_TASK_PANIC
822 
823 config WQ_WATCHDOG
824         bool "Detect Workqueue Stalls"
825         depends on DEBUG_KERNEL
826         help
827           Say Y here to enable stall detection on workqueues.  If a
828           worker pool doesn't make forward progress on a pending work
829           item for over a given amount of time, 30s by default, a
830           warning message is printed along with dump of workqueue
831           state.  This can be configured through kernel parameter
832           "workqueue.watchdog_thresh" and its sysfs counterpart.
833 
834 endmenu # "Debug lockups and hangs"
835 
836 config PANIC_ON_OOPS
837         bool "Panic on Oops"
838         help
839           Say Y here to enable the kernel to panic when it oopses. This
840           has the same effect as setting oops=panic on the kernel command
841           line.
842 
843           This feature is useful to ensure that the kernel does not do
844           anything erroneous after an oops which could result in data
845           corruption or other issues.
846 
847           Say N if unsure.
848 
849 config PANIC_ON_OOPS_VALUE
850         int
851         range 0 1
852         default 0 if !PANIC_ON_OOPS
853         default 1 if PANIC_ON_OOPS
854 
855 config PANIC_TIMEOUT
856         int "panic timeout"
857         default 0
858         help
859           Set the timeout value (in seconds) until a reboot occurs when the
860           the kernel panics. If n = 0, then we wait forever. A timeout
861           value n > 0 will wait n seconds before rebooting, while a timeout
862           value n < 0 will reboot immediately.
863 
864 config SCHED_DEBUG
865         bool "Collect scheduler debugging info"
866         depends on DEBUG_KERNEL && PROC_FS
867         default y
868         help
869           If you say Y here, the /proc/sched_debug file will be provided
870           that can help debug the scheduler. The runtime overhead of this
871           option is minimal.
872 
873 config SCHED_INFO
874         bool
875         default n
876 
877 config SCHEDSTATS
878         bool "Collect scheduler statistics"
879         depends on DEBUG_KERNEL && PROC_FS
880         select SCHED_INFO
881         help
882           If you say Y here, additional code will be inserted into the
883           scheduler and related routines to collect statistics about
884           scheduler behavior and provide them in /proc/schedstat.  These
885           stats may be useful for both tuning and debugging the scheduler
886           If you aren't debugging the scheduler or trying to tune a specific
887           application, you can say N to avoid the very slight overhead
888           this adds.
889 
890 config SCHED_STACK_END_CHECK
891         bool "Detect stack corruption on calls to schedule()"
892         depends on DEBUG_KERNEL
893         default n
894         help
895           This option checks for a stack overrun on calls to schedule().
896           If the stack end location is found to be over written always panic as
897           the content of the corrupted region can no longer be trusted.
898           This is to ensure no erroneous behaviour occurs which could result in
899           data corruption or a sporadic crash at a later stage once the region
900           is examined. The runtime overhead introduced is minimal.
901 
902 config DEBUG_TIMEKEEPING
903         bool "Enable extra timekeeping sanity checking"
904         help
905           This option will enable additional timekeeping sanity checks
906           which may be helpful when diagnosing issues where timekeeping
907           problems are suspected.
908 
909           This may include checks in the timekeeping hotpaths, so this
910           option may have a (very small) performance impact to some
911           workloads.
912 
913           If unsure, say N.
914 
915 config TIMER_STATS
916         bool "Collect kernel timers statistics"
917         depends on DEBUG_KERNEL && PROC_FS
918         help
919           If you say Y here, additional code will be inserted into the
920           timer routines to collect statistics about kernel timers being
921           reprogrammed. The statistics can be read from /proc/timer_stats.
922           The statistics collection is started by writing 1 to /proc/timer_stats,
923           writing 0 stops it. This feature is useful to collect information
924           about timer usage patterns in kernel and userspace. This feature
925           is lightweight if enabled in the kernel config but not activated
926           (it defaults to deactivated on bootup and will only be activated
927           if some application like powertop activates it explicitly).
928 
929 config DEBUG_PREEMPT
930         bool "Debug preemptible kernel"
931         depends on DEBUG_KERNEL && PREEMPT && TRACE_IRQFLAGS_SUPPORT
932         default y
933         help
934           If you say Y here then the kernel will use a debug variant of the
935           commonly used smp_processor_id() function and will print warnings
936           if kernel code uses it in a preemption-unsafe way. Also, the kernel
937           will detect preemption count underflows.
938 
939 menu "Lock Debugging (spinlocks, mutexes, etc...)"
940 
941 config DEBUG_RT_MUTEXES
942         bool "RT Mutex debugging, deadlock detection"
943         depends on DEBUG_KERNEL && RT_MUTEXES
944         help
945          This allows rt mutex semantics violations and rt mutex related
946          deadlocks (lockups) to be detected and reported automatically.
947 
948 config DEBUG_SPINLOCK
949         bool "Spinlock and rw-lock debugging: basic checks"
950         depends on DEBUG_KERNEL
951         select UNINLINE_SPIN_UNLOCK
952         help
953           Say Y here and build SMP to catch missing spinlock initialization
954           and certain other kinds of spinlock errors commonly made.  This is
955           best used in conjunction with the NMI watchdog so that spinlock
956           deadlocks are also debuggable.
957 
958 config DEBUG_MUTEXES
959         bool "Mutex debugging: basic checks"
960         depends on DEBUG_KERNEL
961         help
962          This feature allows mutex semantics violations to be detected and
963          reported.
964 
965 config DEBUG_WW_MUTEX_SLOWPATH
966         bool "Wait/wound mutex debugging: Slowpath testing"
967         depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT
968         select DEBUG_LOCK_ALLOC
969         select DEBUG_SPINLOCK
970         select DEBUG_MUTEXES
971         help
972          This feature enables slowpath testing for w/w mutex users by
973          injecting additional -EDEADLK wound/backoff cases. Together with
974          the full mutex checks enabled with (CONFIG_PROVE_LOCKING) this
975          will test all possible w/w mutex interface abuse with the
976          exception of simply not acquiring all the required locks.
977          Note that this feature can introduce significant overhead, so
978          it really should not be enabled in a production or distro kernel,
979          even a debug kernel.  If you are a driver writer, enable it.  If
980          you are a distro, do not.
981 
982 config DEBUG_LOCK_ALLOC
983         bool "Lock debugging: detect incorrect freeing of live locks"
984         depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT
985         select DEBUG_SPINLOCK
986         select DEBUG_MUTEXES
987         select LOCKDEP
988         help
989          This feature will check whether any held lock (spinlock, rwlock,
990          mutex or rwsem) is incorrectly freed by the kernel, via any of the
991          memory-freeing routines (kfree(), kmem_cache_free(), free_pages(),
992          vfree(), etc.), whether a live lock is incorrectly reinitialized via
993          spin_lock_init()/mutex_init()/etc., or whether there is any lock
994          held during task exit.
995 
996 config PROVE_LOCKING
997         bool "Lock debugging: prove locking correctness"
998         depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT
999         select LOCKDEP
1000         select DEBUG_SPINLOCK
1001         select DEBUG_MUTEXES
1002         select DEBUG_LOCK_ALLOC
1003         select TRACE_IRQFLAGS
1004         default n
1005         help
1006          This feature enables the kernel to prove that all locking
1007          that occurs in the kernel runtime is mathematically
1008          correct: that under no circumstance could an arbitrary (and
1009          not yet triggered) combination of observed locking
1010          sequences (on an arbitrary number of CPUs, running an
1011          arbitrary number of tasks and interrupt contexts) cause a
1012          deadlock.
1013 
1014          In short, this feature enables the kernel to report locking
1015          related deadlocks before they actually occur.
1016 
1017          The proof does not depend on how hard and complex a
1018          deadlock scenario would be to trigger: how many
1019          participant CPUs, tasks and irq-contexts would be needed
1020          for it to trigger. The proof also does not depend on
1021          timing: if a race and a resulting deadlock is possible
1022          theoretically (no matter how unlikely the race scenario
1023          is), it will be proven so and will immediately be
1024          reported by the kernel (once the event is observed that
1025          makes the deadlock theoretically possible).
1026 
1027          If a deadlock is impossible (i.e. the locking rules, as
1028          observed by the kernel, are mathematically correct), the
1029          kernel reports nothing.
1030 
1031          NOTE: this feature can also be enabled for rwlocks, mutexes
1032          and rwsems - in which case all dependencies between these
1033          different locking variants are observed and mapped too, and
1034          the proof of observed correctness is also maintained for an
1035          arbitrary combination of these separate locking variants.
1036 
1037          For more details, see Documentation/locking/lockdep-design.txt.
1038 
1039 config LOCKDEP
1040         bool
1041         depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT
1042         select STACKTRACE
1043         select FRAME_POINTER if !MIPS && !PPC && !ARM_UNWIND && !S390 && !MICROBLAZE && !ARC && !SCORE
1044         select KALLSYMS
1045         select KALLSYMS_ALL
1046 
1047 config LOCK_STAT
1048         bool "Lock usage statistics"
1049         depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT
1050         select LOCKDEP
1051         select DEBUG_SPINLOCK
1052         select DEBUG_MUTEXES
1053         select DEBUG_LOCK_ALLOC
1054         default n
1055         help
1056          This feature enables tracking lock contention points
1057 
1058          For more details, see Documentation/locking/lockstat.txt
1059 
1060          This also enables lock events required by "perf lock",
1061          subcommand of perf.
1062          If you want to use "perf lock", you also need to turn on
1063          CONFIG_EVENT_TRACING.
1064 
1065          CONFIG_LOCK_STAT defines "contended" and "acquired" lock events.
1066          (CONFIG_LOCKDEP defines "acquire" and "release" events.)
1067 
1068 config DEBUG_LOCKDEP
1069         bool "Lock dependency engine debugging"
1070         depends on DEBUG_KERNEL && LOCKDEP
1071         help
1072           If you say Y here, the lock dependency engine will do
1073           additional runtime checks to debug itself, at the price
1074           of more runtime overhead.
1075 
1076 config DEBUG_ATOMIC_SLEEP
1077         bool "Sleep inside atomic section checking"
1078         select PREEMPT_COUNT
1079         depends on DEBUG_KERNEL
1080         help
1081           If you say Y here, various routines which may sleep will become very
1082           noisy if they are called inside atomic sections: when a spinlock is
1083           held, inside an rcu read side critical section, inside preempt disabled
1084           sections, inside an interrupt, etc...
1085 
1086 config DEBUG_LOCKING_API_SELFTESTS
1087         bool "Locking API boot-time self-tests"
1088         depends on DEBUG_KERNEL
1089         help
1090           Say Y here if you want the kernel to run a short self-test during
1091           bootup. The self-test checks whether common types of locking bugs
1092           are detected by debugging mechanisms or not. (if you disable
1093           lock debugging then those bugs wont be detected of course.)
1094           The following locking APIs are covered: spinlocks, rwlocks,
1095           mutexes and rwsems.
1096 
1097 config LOCK_TORTURE_TEST
1098         tristate "torture tests for locking"
1099         depends on DEBUG_KERNEL
1100         select TORTURE_TEST
1101         default n
1102         help
1103           This option provides a kernel module that runs torture tests
1104           on kernel locking primitives.  The kernel module may be built
1105           after the fact on the running kernel to be tested, if desired.
1106 
1107           Say Y here if you want kernel locking-primitive torture tests
1108           to be built into the kernel.
1109           Say M if you want these torture tests to build as a module.
1110           Say N if you are unsure.
1111 
1112 endmenu # lock debugging
1113 
1114 config TRACE_IRQFLAGS
1115         bool
1116         help
1117           Enables hooks to interrupt enabling and disabling for
1118           either tracing or lock debugging.
1119 
1120 config STACKTRACE
1121         bool "Stack backtrace support"
1122         depends on STACKTRACE_SUPPORT
1123         help
1124           This option causes the kernel to create a /proc/pid/stack for
1125           every process, showing its current stack trace.
1126           It is also used by various kernel debugging features that require
1127           stack trace generation.
1128 
1129 config DEBUG_KOBJECT
1130         bool "kobject debugging"
1131         depends on DEBUG_KERNEL
1132         help
1133           If you say Y here, some extra kobject debugging messages will be sent
1134           to the syslog. 
1135 
1136 config DEBUG_KOBJECT_RELEASE
1137         bool "kobject release debugging"
1138         depends on DEBUG_OBJECTS_TIMERS
1139         help
1140           kobjects are reference counted objects.  This means that their
1141           last reference count put is not predictable, and the kobject can
1142           live on past the point at which a driver decides to drop it's
1143           initial reference to the kobject gained on allocation.  An
1144           example of this would be a struct device which has just been
1145           unregistered.
1146 
1147           However, some buggy drivers assume that after such an operation,
1148           the memory backing the kobject can be immediately freed.  This
1149           goes completely against the principles of a refcounted object.
1150 
1151           If you say Y here, the kernel will delay the release of kobjects
1152           on the last reference count to improve the visibility of this
1153           kind of kobject release bug.
1154 
1155 config HAVE_DEBUG_BUGVERBOSE
1156         bool
1157 
1158 config DEBUG_BUGVERBOSE
1159         bool "Verbose BUG() reporting (adds 70K)" if DEBUG_KERNEL && EXPERT
1160         depends on BUG && (GENERIC_BUG || HAVE_DEBUG_BUGVERBOSE)
1161         default y
1162         help
1163           Say Y here to make BUG() panics output the file name and line number
1164           of the BUG call as well as the EIP and oops trace.  This aids
1165           debugging but costs about 70-100K of memory.
1166 
1167 config DEBUG_LIST
1168         bool "Debug linked list manipulation"
1169         depends on DEBUG_KERNEL
1170         help
1171           Enable this to turn on extended checks in the linked-list
1172           walking routines.
1173 
1174           If unsure, say N.
1175 
1176 config DEBUG_PI_LIST
1177         bool "Debug priority linked list manipulation"
1178         depends on DEBUG_KERNEL
1179         help
1180           Enable this to turn on extended checks in the priority-ordered
1181           linked-list (plist) walking routines.  This checks the entire
1182           list multiple times during each manipulation.
1183 
1184           If unsure, say N.
1185 
1186 config DEBUG_SG
1187         bool "Debug SG table operations"
1188         depends on DEBUG_KERNEL
1189         help
1190           Enable this to turn on checks on scatter-gather tables. This can
1191           help find problems with drivers that do not properly initialize
1192           their sg tables.
1193 
1194           If unsure, say N.
1195 
1196 config DEBUG_NOTIFIERS
1197         bool "Debug notifier call chains"
1198         depends on DEBUG_KERNEL
1199         help
1200           Enable this to turn on sanity checking for notifier call chains.
1201           This is most useful for kernel developers to make sure that
1202           modules properly unregister themselves from notifier chains.
1203           This is a relatively cheap check but if you care about maximum
1204           performance, say N.
1205 
1206 config DEBUG_CREDENTIALS
1207         bool "Debug credential management"
1208         depends on DEBUG_KERNEL
1209         help
1210           Enable this to turn on some debug checking for credential
1211           management.  The additional code keeps track of the number of
1212           pointers from task_structs to any given cred struct, and checks to
1213           see that this number never exceeds the usage count of the cred
1214           struct.
1215 
1216           Furthermore, if SELinux is enabled, this also checks that the
1217           security pointer in the cred struct is never seen to be invalid.
1218 
1219           If unsure, say N.
1220 
1221 menu "RCU Debugging"
1222 
1223 config PROVE_RCU
1224         def_bool PROVE_LOCKING
1225 
1226 config PROVE_RCU_REPEATEDLY
1227         bool "RCU debugging: don't disable PROVE_RCU on first splat"
1228         depends on PROVE_RCU
1229         default n
1230         help
1231          By itself, PROVE_RCU will disable checking upon issuing the
1232          first warning (or "splat").  This feature prevents such
1233          disabling, allowing multiple RCU-lockdep warnings to be printed
1234          on a single reboot.
1235 
1236          Say Y to allow multiple RCU-lockdep warnings per boot.
1237 
1238          Say N if you are unsure.
1239 
1240 config SPARSE_RCU_POINTER
1241         bool "RCU debugging: sparse-based checks for pointer usage"
1242         default n
1243         help
1244          This feature enables the __rcu sparse annotation for
1245          RCU-protected pointers.  This annotation will cause sparse
1246          to flag any non-RCU used of annotated pointers.  This can be
1247          helpful when debugging RCU usage.  Please note that this feature
1248          is not intended to enforce code cleanliness; it is instead merely
1249          a debugging aid.
1250 
1251          Say Y to make sparse flag questionable use of RCU-protected pointers
1252 
1253          Say N if you are unsure.
1254 
1255 config TORTURE_TEST
1256         tristate
1257         default n
1258 
1259 config RCU_TORTURE_TEST
1260         tristate "torture tests for RCU"
1261         depends on DEBUG_KERNEL
1262         select TORTURE_TEST
1263         select SRCU
1264         select TASKS_RCU
1265         default n
1266         help
1267           This option provides a kernel module that runs torture tests
1268           on the RCU infrastructure.  The kernel module may be built
1269           after the fact on the running kernel to be tested, if desired.
1270 
1271           Say Y here if you want RCU torture tests to be built into
1272           the kernel.
1273           Say M if you want the RCU torture tests to build as a module.
1274           Say N if you are unsure.
1275 
1276 config RCU_TORTURE_TEST_RUNNABLE
1277         bool "torture tests for RCU runnable by default"
1278         depends on RCU_TORTURE_TEST = y
1279         default n
1280         help
1281           This option provides a way to build the RCU torture tests
1282           directly into the kernel without them starting up at boot
1283           time.  You can use /proc/sys/kernel/rcutorture_runnable
1284           to manually override this setting.  This /proc file is
1285           available only when the RCU torture tests have been built
1286           into the kernel.
1287 
1288           Say Y here if you want the RCU torture tests to start during
1289           boot (you probably don't).
1290           Say N here if you want the RCU torture tests to start only
1291           after being manually enabled via /proc.
1292 
1293 config RCU_TORTURE_TEST_SLOW_PREINIT
1294         bool "Slow down RCU grace-period pre-initialization to expose races"
1295         depends on RCU_TORTURE_TEST
1296         help
1297           This option delays grace-period pre-initialization (the
1298           propagation of CPU-hotplug changes up the rcu_node combining
1299           tree) for a few jiffies between initializing each pair of
1300           consecutive rcu_node structures.  This helps to expose races
1301           involving grace-period pre-initialization, in other words, it
1302           makes your kernel less stable.  It can also greatly increase
1303           grace-period latency, especially on systems with large numbers
1304           of CPUs.  This is useful when torture-testing RCU, but in
1305           almost no other circumstance.
1306 
1307           Say Y here if you want your system to crash and hang more often.
1308           Say N if you want a sane system.
1309 
1310 config RCU_TORTURE_TEST_SLOW_PREINIT_DELAY
1311         int "How much to slow down RCU grace-period pre-initialization"
1312         range 0 5
1313         default 3
1314         depends on RCU_TORTURE_TEST_SLOW_PREINIT
1315         help
1316           This option specifies the number of jiffies to wait between
1317           each rcu_node structure pre-initialization step.
1318 
1319 config RCU_TORTURE_TEST_SLOW_INIT
1320         bool "Slow down RCU grace-period initialization to expose races"
1321         depends on RCU_TORTURE_TEST
1322         help
1323           This option delays grace-period initialization for a few
1324           jiffies between initializing each pair of consecutive
1325           rcu_node structures.  This helps to expose races involving
1326           grace-period initialization, in other words, it makes your
1327           kernel less stable.  It can also greatly increase grace-period
1328           latency, especially on systems with large numbers of CPUs.
1329           This is useful when torture-testing RCU, but in almost no
1330           other circumstance.
1331 
1332           Say Y here if you want your system to crash and hang more often.
1333           Say N if you want a sane system.
1334 
1335 config RCU_TORTURE_TEST_SLOW_INIT_DELAY
1336         int "How much to slow down RCU grace-period initialization"
1337         range 0 5
1338         default 3
1339         depends on RCU_TORTURE_TEST_SLOW_INIT
1340         help
1341           This option specifies the number of jiffies to wait between
1342           each rcu_node structure initialization.
1343 
1344 config RCU_TORTURE_TEST_SLOW_CLEANUP
1345         bool "Slow down RCU grace-period cleanup to expose races"
1346         depends on RCU_TORTURE_TEST
1347         help
1348           This option delays grace-period cleanup for a few jiffies
1349           between cleaning up each pair of consecutive rcu_node
1350           structures.  This helps to expose races involving grace-period
1351           cleanup, in other words, it makes your kernel less stable.
1352           It can also greatly increase grace-period latency, especially
1353           on systems with large numbers of CPUs.  This is useful when
1354           torture-testing RCU, but in almost no other circumstance.
1355 
1356           Say Y here if you want your system to crash and hang more often.
1357           Say N if you want a sane system.
1358 
1359 config RCU_TORTURE_TEST_SLOW_CLEANUP_DELAY
1360         int "How much to slow down RCU grace-period cleanup"
1361         range 0 5
1362         default 3
1363         depends on RCU_TORTURE_TEST_SLOW_CLEANUP
1364         help
1365           This option specifies the number of jiffies to wait between
1366           each rcu_node structure cleanup operation.
1367 
1368 config RCU_CPU_STALL_TIMEOUT
1369         int "RCU CPU stall timeout in seconds"
1370         depends on RCU_STALL_COMMON
1371         range 3 300
1372         default 21
1373         help
1374           If a given RCU grace period extends more than the specified
1375           number of seconds, a CPU stall warning is printed.  If the
1376           RCU grace period persists, additional CPU stall warnings are
1377           printed at more widely spaced intervals.
1378 
1379 config RCU_TRACE
1380         bool "Enable tracing for RCU"
1381         depends on DEBUG_KERNEL
1382         select TRACE_CLOCK
1383         help
1384           This option provides tracing in RCU which presents stats
1385           in debugfs for debugging RCU implementation.
1386 
1387           Say Y here if you want to enable RCU tracing
1388           Say N if you are unsure.
1389 
1390 config RCU_EQS_DEBUG
1391         bool "Provide debugging asserts for adding NO_HZ support to an arch"
1392         depends on DEBUG_KERNEL
1393         help
1394           This option provides consistency checks in RCU's handling of
1395           NO_HZ.  These checks have proven quite helpful in detecting
1396           bugs in arch-specific NO_HZ code.
1397 
1398           Say N here if you need ultimate kernel/user switch latencies
1399           Say Y if you are unsure
1400 
1401 endmenu # "RCU Debugging"
1402 
1403 config DEBUG_WQ_FORCE_RR_CPU
1404         bool "Force round-robin CPU selection for unbound work items"
1405         depends on DEBUG_KERNEL
1406         default n
1407         help
1408           Workqueue used to implicitly guarantee that work items queued
1409           without explicit CPU specified are put on the local CPU.  This
1410           guarantee is no longer true and while local CPU is still
1411           preferred work items may be put on foreign CPUs.  Kernel
1412           parameter "workqueue.debug_force_rr_cpu" is added to force
1413           round-robin CPU selection to flush out usages which depend on the
1414           now broken guarantee.  This config option enables the debug
1415           feature by default.  When enabled, memory and cache locality will
1416           be impacted.
1417 
1418 config DEBUG_BLOCK_EXT_DEVT
1419         bool "Force extended block device numbers and spread them"
1420         depends on DEBUG_KERNEL
1421         depends on BLOCK
1422         default n
1423         help
1424           BIG FAT WARNING: ENABLING THIS OPTION MIGHT BREAK BOOTING ON
1425           SOME DISTRIBUTIONS.  DO NOT ENABLE THIS UNLESS YOU KNOW WHAT
1426           YOU ARE DOING.  Distros, please enable this and fix whatever
1427           is broken.
1428 
1429           Conventionally, block device numbers are allocated from
1430           predetermined contiguous area.  However, extended block area
1431           may introduce non-contiguous block device numbers.  This
1432           option forces most block device numbers to be allocated from
1433           the extended space and spreads them to discover kernel or
1434           userland code paths which assume predetermined contiguous
1435           device number allocation.
1436 
1437           Note that turning on this debug option shuffles all the
1438           device numbers for all IDE and SCSI devices including libata
1439           ones, so root partition specified using device number
1440           directly (via rdev or root=MAJ:MIN) won't work anymore.
1441           Textual device names (root=/dev/sdXn) will continue to work.
1442 
1443           Say N if you are unsure.
1444 
1445 config NOTIFIER_ERROR_INJECTION
1446         tristate "Notifier error injection"
1447         depends on DEBUG_KERNEL
1448         select DEBUG_FS
1449         help
1450           This option provides the ability to inject artificial errors to
1451           specified notifier chain callbacks. It is useful to test the error
1452           handling of notifier call chain failures.
1453 
1454           Say N if unsure.
1455 
1456 config CPU_NOTIFIER_ERROR_INJECT
1457         tristate "CPU notifier error injection module"
1458         depends on HOTPLUG_CPU && NOTIFIER_ERROR_INJECTION
1459         help
1460           This option provides a kernel module that can be used to test
1461           the error handling of the cpu notifiers by injecting artificial
1462           errors to CPU notifier chain callbacks.  It is controlled through
1463           debugfs interface under /sys/kernel/debug/notifier-error-inject/cpu
1464 
1465           If the notifier call chain should be failed with some events
1466           notified, write the error code to "actions/<notifier event>/error".
1467 
1468           Example: Inject CPU offline error (-1 == -EPERM)
1469 
1470           # cd /sys/kernel/debug/notifier-error-inject/cpu
1471           # echo -1 > actions/CPU_DOWN_PREPARE/error
1472           # echo 0 > /sys/devices/system/cpu/cpu1/online
1473           bash: echo: write error: Operation not permitted
1474 
1475           To compile this code as a module, choose M here: the module will
1476           be called cpu-notifier-error-inject.
1477 
1478           If unsure, say N.
1479 
1480 config PM_NOTIFIER_ERROR_INJECT
1481         tristate "PM notifier error injection module"
1482         depends on PM && NOTIFIER_ERROR_INJECTION
1483         default m if PM_DEBUG
1484         help
1485           This option provides the ability to inject artificial errors to
1486           PM notifier chain callbacks.  It is controlled through debugfs
1487           interface /sys/kernel/debug/notifier-error-inject/pm
1488 
1489           If the notifier call chain should be failed with some events
1490           notified, write the error code to "actions/<notifier event>/error".
1491 
1492           Example: Inject PM suspend error (-12 = -ENOMEM)
1493 
1494           # cd /sys/kernel/debug/notifier-error-inject/pm/
1495           # echo -12 > actions/PM_SUSPEND_PREPARE/error
1496           # echo mem > /sys/power/state
1497           bash: echo: write error: Cannot allocate memory
1498 
1499           To compile this code as a module, choose M here: the module will
1500           be called pm-notifier-error-inject.
1501 
1502           If unsure, say N.
1503 
1504 config OF_RECONFIG_NOTIFIER_ERROR_INJECT
1505         tristate "OF reconfig notifier error injection module"
1506         depends on OF_DYNAMIC && NOTIFIER_ERROR_INJECTION
1507         help
1508           This option provides the ability to inject artificial errors to
1509           OF reconfig notifier chain callbacks.  It is controlled
1510           through debugfs interface under
1511           /sys/kernel/debug/notifier-error-inject/OF-reconfig/
1512 
1513           If the notifier call chain should be failed with some events
1514           notified, write the error code to "actions/<notifier event>/error".
1515 
1516           To compile this code as a module, choose M here: the module will
1517           be called of-reconfig-notifier-error-inject.
1518 
1519           If unsure, say N.
1520 
1521 config NETDEV_NOTIFIER_ERROR_INJECT
1522         tristate "Netdev notifier error injection module"
1523         depends on NET && NOTIFIER_ERROR_INJECTION
1524         help
1525           This option provides the ability to inject artificial errors to
1526           netdevice notifier chain callbacks.  It is controlled through debugfs
1527           interface /sys/kernel/debug/notifier-error-inject/netdev
1528 
1529           If the notifier call chain should be failed with some events
1530           notified, write the error code to "actions/<notifier event>/error".
1531 
1532           Example: Inject netdevice mtu change error (-22 = -EINVAL)
1533 
1534           # cd /sys/kernel/debug/notifier-error-inject/netdev
1535           # echo -22 > actions/NETDEV_CHANGEMTU/error
1536           # ip link set eth0 mtu 1024
1537           RTNETLINK answers: Invalid argument
1538 
1539           To compile this code as a module, choose M here: the module will
1540           be called netdev-notifier-error-inject.
1541 
1542           If unsure, say N.
1543 
1544 config FAULT_INJECTION
1545         bool "Fault-injection framework"
1546         depends on DEBUG_KERNEL
1547         help
1548           Provide fault-injection framework.
1549           For more details, see Documentation/fault-injection/.
1550 
1551 config FAILSLAB
1552         bool "Fault-injection capability for kmalloc"
1553         depends on FAULT_INJECTION
1554         depends on SLAB || SLUB
1555         help
1556           Provide fault-injection capability for kmalloc.
1557 
1558 config FAIL_PAGE_ALLOC
1559         bool "Fault-injection capabilitiy for alloc_pages()"
1560         depends on FAULT_INJECTION
1561         help
1562           Provide fault-injection capability for alloc_pages().
1563 
1564 config FAIL_MAKE_REQUEST
1565         bool "Fault-injection capability for disk IO"
1566         depends on FAULT_INJECTION && BLOCK
1567         help
1568           Provide fault-injection capability for disk IO.
1569 
1570 config FAIL_IO_TIMEOUT
1571         bool "Fault-injection capability for faking disk interrupts"
1572         depends on FAULT_INJECTION && BLOCK
1573         help
1574           Provide fault-injection capability on end IO handling. This
1575           will make the block layer "forget" an interrupt as configured,
1576           thus exercising the error handling.
1577 
1578           Only works with drivers that use the generic timeout handling,
1579           for others it wont do anything.
1580 
1581 config FAIL_MMC_REQUEST
1582         bool "Fault-injection capability for MMC IO"
1583         depends on FAULT_INJECTION_DEBUG_FS && MMC
1584         help
1585           Provide fault-injection capability for MMC IO.
1586           This will make the mmc core return data errors. This is
1587           useful to test the error handling in the mmc block device
1588           and to test how the mmc host driver handles retries from
1589           the block device.
1590 
1591 config FAIL_FUTEX
1592         bool "Fault-injection capability for futexes"
1593         select DEBUG_FS
1594         depends on FAULT_INJECTION && FUTEX
1595         help
1596           Provide fault-injection capability for futexes.
1597 
1598 config FAULT_INJECTION_DEBUG_FS
1599         bool "Debugfs entries for fault-injection capabilities"
1600         depends on FAULT_INJECTION && SYSFS && DEBUG_FS
1601         help
1602           Enable configuration of fault-injection capabilities via debugfs.
1603 
1604 config FAULT_INJECTION_STACKTRACE_FILTER
1605         bool "stacktrace filter for fault-injection capabilities"
1606         depends on FAULT_INJECTION_DEBUG_FS && STACKTRACE_SUPPORT
1607         depends on !X86_64
1608         select STACKTRACE
1609         select FRAME_POINTER if !MIPS && !PPC && !S390 && !MICROBLAZE && !ARM_UNWIND && !ARC && !SCORE
1610         help
1611           Provide stacktrace filter for fault-injection capabilities
1612 
1613 config LATENCYTOP
1614         bool "Latency measuring infrastructure"
1615         depends on DEBUG_KERNEL
1616         depends on STACKTRACE_SUPPORT
1617         depends on PROC_FS
1618         select FRAME_POINTER if !MIPS && !PPC && !S390 && !MICROBLAZE && !ARM_UNWIND && !ARC
1619         select KALLSYMS
1620         select KALLSYMS_ALL
1621         select STACKTRACE
1622         select SCHEDSTATS
1623         select SCHED_DEBUG
1624         help
1625           Enable this option if you want to use the LatencyTOP tool
1626           to find out which userspace is blocking on what kernel operations.
1627 
1628 config ARCH_HAS_DEBUG_STRICT_USER_COPY_CHECKS
1629         bool
1630 
1631 config DEBUG_STRICT_USER_COPY_CHECKS
1632         bool "Strict user copy size checks"
1633         depends on ARCH_HAS_DEBUG_STRICT_USER_COPY_CHECKS
1634         depends on DEBUG_KERNEL && !TRACE_BRANCH_PROFILING
1635         help
1636           Enabling this option turns a certain set of sanity checks for user
1637           copy operations into compile time failures.
1638 
1639           The copy_from_user() etc checks are there to help test if there
1640           are sufficient security checks on the length argument of
1641           the copy operation, by having gcc prove that the argument is
1642           within bounds.
1643 
1644           If unsure, say N.
1645 
1646 source kernel/trace/Kconfig
1647 
1648 menu "Runtime Testing"
1649 
1650 config LKDTM
1651         tristate "Linux Kernel Dump Test Tool Module"
1652         depends on DEBUG_FS
1653         depends on BLOCK
1654         default n
1655         help
1656         This module enables testing of the different dumping mechanisms by
1657         inducing system failures at predefined crash points.
1658         If you don't need it: say N
1659         Choose M here to compile this code as a module. The module will be
1660         called lkdtm.
1661 
1662         Documentation on how to use the module can be found in
1663         Documentation/fault-injection/provoke-crashes.txt
1664 
1665 config TEST_LIST_SORT
1666         bool "Linked list sorting test"
1667         depends on DEBUG_KERNEL
1668         help
1669           Enable this to turn on 'list_sort()' function test. This test is
1670           executed only once during system boot, so affects only boot time.
1671 
1672           If unsure, say N.
1673 
1674 config KPROBES_SANITY_TEST
1675         bool "Kprobes sanity tests"
1676         depends on DEBUG_KERNEL
1677         depends on KPROBES
1678         default n
1679         help
1680           This option provides for testing basic kprobes functionality on
1681           boot. A sample kprobe, jprobe and kretprobe are inserted and
1682           verified for functionality.
1683 
1684           Say N if you are unsure.
1685 
1686 config BACKTRACE_SELF_TEST
1687         tristate "Self test for the backtrace code"
1688         depends on DEBUG_KERNEL
1689         default n
1690         help
1691           This option provides a kernel module that can be used to test
1692           the kernel stack backtrace code. This option is not useful
1693           for distributions or general kernels, but only for kernel
1694           developers working on architecture code.
1695 
1696           Note that if you want to also test saved backtraces, you will
1697           have to enable STACKTRACE as well.
1698 
1699           Say N if you are unsure.
1700 
1701 config RBTREE_TEST
1702         tristate "Red-Black tree test"
1703         depends on DEBUG_KERNEL
1704         help
1705           A benchmark measuring the performance of the rbtree library.
1706           Also includes rbtree invariant checks.
1707 
1708 config INTERVAL_TREE_TEST
1709         tristate "Interval tree test"
1710         depends on m && DEBUG_KERNEL
1711         select INTERVAL_TREE
1712         help
1713           A benchmark measuring the performance of the interval tree library
1714 
1715 config PERCPU_TEST
1716         tristate "Per cpu operations test"
1717         depends on m && DEBUG_KERNEL
1718         help
1719           Enable this option to build test module which validates per-cpu
1720           operations.
1721 
1722           If unsure, say N.
1723 
1724 config ATOMIC64_SELFTEST
1725         bool "Perform an atomic64_t self-test at boot"
1726         help
1727           Enable this option to test the atomic64_t functions at boot.
1728 
1729           If unsure, say N.
1730 
1731 config ASYNC_RAID6_TEST
1732         tristate "Self test for hardware accelerated raid6 recovery"
1733         depends on ASYNC_RAID6_RECOV
1734         select ASYNC_MEMCPY
1735         ---help---
1736           This is a one-shot self test that permutes through the
1737           recovery of all the possible two disk failure scenarios for a
1738           N-disk array.  Recovery is performed with the asynchronous
1739           raid6 recovery routines, and will optionally use an offload
1740           engine if one is available.
1741 
1742           If unsure, say N.
1743 
1744 config TEST_HEXDUMP
1745         tristate "Test functions located in the hexdump module at runtime"
1746 
1747 config TEST_STRING_HELPERS
1748         tristate "Test functions located in the string_helpers module at runtime"
1749 
1750 config TEST_KSTRTOX
1751         tristate "Test kstrto*() family of functions at runtime"
1752 
1753 config TEST_PRINTF
1754         tristate "Test printf() family of functions at runtime"
1755 
1756 config TEST_RHASHTABLE
1757         tristate "Perform selftest on resizable hash table"
1758         default n
1759         help
1760           Enable this option to test the rhashtable functions at boot.
1761 
1762           If unsure, say N.
1763 
1764 endmenu # runtime tests
1765 
1766 config PROVIDE_OHCI1394_DMA_INIT
1767         bool "Remote debugging over FireWire early on boot"
1768         depends on PCI && X86
1769         help
1770           If you want to debug problems which hang or crash the kernel early
1771           on boot and the crashing machine has a FireWire port, you can use
1772           this feature to remotely access the memory of the crashed machine
1773           over FireWire. This employs remote DMA as part of the OHCI1394
1774           specification which is now the standard for FireWire controllers.
1775 
1776           With remote DMA, you can monitor the printk buffer remotely using
1777           firescope and access all memory below 4GB using fireproxy from gdb.
1778           Even controlling a kernel debugger is possible using remote DMA.
1779 
1780           Usage:
1781 
1782           If ohci1394_dma=early is used as boot parameter, it will initialize
1783           all OHCI1394 controllers which are found in the PCI config space.
1784 
1785           As all changes to the FireWire bus such as enabling and disabling
1786           devices cause a bus reset and thereby disable remote DMA for all
1787           devices, be sure to have the cable plugged and FireWire enabled on
1788           the debugging host before booting the debug target for debugging.
1789 
1790           This code (~1k) is freed after boot. By then, the firewire stack
1791           in charge of the OHCI-1394 controllers should be used instead.
1792 
1793           See Documentation/debugging-via-ohci1394.txt for more information.
1794 
1795 config BUILD_DOCSRC
1796         bool "Build targets in Documentation/ tree"
1797         depends on HEADERS_CHECK
1798         help
1799           This option attempts to build objects from the source files in the
1800           kernel Documentation/ tree.
1801 
1802           Say N if you are unsure.
1803 
1804 config DMA_API_DEBUG
1805         bool "Enable debugging of DMA-API usage"
1806         depends on HAVE_DMA_API_DEBUG
1807         help
1808           Enable this option to debug the use of the DMA API by device drivers.
1809           With this option you will be able to detect common bugs in device
1810           drivers like double-freeing of DMA mappings or freeing mappings that
1811           were never allocated.
1812 
1813           This also attempts to catch cases where a page owned by DMA is
1814           accessed by the cpu in a way that could cause data corruption.  For
1815           example, this enables cow_user_page() to check that the source page is
1816           not undergoing DMA.
1817 
1818           This option causes a performance degradation.  Use only if you want to
1819           debug device drivers and dma interactions.
1820 
1821           If unsure, say N.
1822 
1823 config TEST_LKM
1824         tristate "Test module loading with 'hello world' module"
1825         default n
1826         depends on m
1827         help
1828           This builds the "test_module" module that emits "Hello, world"
1829           on printk when loaded. It is designed to be used for basic
1830           evaluation of the module loading subsystem (for example when
1831           validating module verification). It lacks any extra dependencies,
1832           and will not normally be loaded by the system unless explicitly
1833           requested by name.
1834 
1835           If unsure, say N.
1836 
1837 config TEST_USER_COPY
1838         tristate "Test user/kernel boundary protections"
1839         default n
1840         depends on m
1841         help
1842           This builds the "test_user_copy" module that runs sanity checks
1843           on the copy_to/from_user infrastructure, making sure basic
1844           user/kernel boundary testing is working. If it fails to load,
1845           a regression has been detected in the user/kernel memory boundary
1846           protections.
1847 
1848           If unsure, say N.
1849 
1850 config TEST_BPF
1851         tristate "Test BPF filter functionality"
1852         default n
1853         depends on m && NET
1854         help
1855           This builds the "test_bpf" module that runs various test vectors
1856           against the BPF interpreter or BPF JIT compiler depending on the
1857           current setting. This is in particular useful for BPF JIT compiler
1858           development, but also to run regression tests against changes in
1859           the interpreter code. It also enables test stubs for eBPF maps and
1860           verifier used by user space verifier testsuite.
1861 
1862           If unsure, say N.
1863 
1864 config TEST_FIRMWARE
1865         tristate "Test firmware loading via userspace interface"
1866         default n
1867         depends on FW_LOADER
1868         help
1869           This builds the "test_firmware" module that creates a userspace
1870           interface for testing firmware loading. This can be used to
1871           control the triggering of firmware loading without needing an
1872           actual firmware-using device. The contents can be rechecked by
1873           userspace.
1874 
1875           If unsure, say N.
1876 
1877 config TEST_UDELAY
1878         tristate "udelay test driver"
1879         default n
1880         help
1881           This builds the "udelay_test" module that helps to make sure
1882           that udelay() is working properly.
1883 
1884           If unsure, say N.
1885 
1886 config MEMTEST
1887         bool "Memtest"
1888         depends on HAVE_MEMBLOCK
1889         ---help---
1890           This option adds a kernel parameter 'memtest', which allows memtest
1891           to be set.
1892                 memtest=0, mean disabled; -- default
1893                 memtest=1, mean do 1 test pattern;
1894                 ...
1895                 memtest=17, mean do 17 test patterns.
1896           If you are unsure how to answer this question, answer N.
1897 
1898 config TEST_STATIC_KEYS
1899         tristate "Test static keys"
1900         default n
1901         depends on m
1902         help
1903           Test the static key interfaces.
1904 
1905           If unsure, say N.
1906 
1907 source "samples/Kconfig"
1908 
1909 source "lib/Kconfig.kgdb"
1910 
1911 source "lib/Kconfig.ubsan"
1912 
1913 config ARCH_HAS_DEVMEM_IS_ALLOWED
1914         bool
1915 
1916 config STRICT_DEVMEM
1917         bool "Filter access to /dev/mem"
1918         depends on MMU
1919         depends on ARCH_HAS_DEVMEM_IS_ALLOWED
1920         default y if TILE || PPC
1921         ---help---
1922           If this option is disabled, you allow userspace (root) access to all
1923           of memory, including kernel and userspace memory. Accidental
1924           access to this is obviously disastrous, but specific access can
1925           be used by people debugging the kernel. Note that with PAT support
1926           enabled, even in this case there are restrictions on /dev/mem
1927           use due to the cache aliasing requirements.
1928 
1929           If this option is switched on, and IO_STRICT_DEVMEM=n, the /dev/mem
1930           file only allows userspace access to PCI space and the BIOS code and
1931           data regions.  This is sufficient for dosemu and X and all common
1932           users of /dev/mem.
1933 
1934           If in doubt, say Y.
1935 
1936 config IO_STRICT_DEVMEM
1937         bool "Filter I/O access to /dev/mem"
1938         depends on STRICT_DEVMEM
1939         ---help---
1940           If this option is disabled, you allow userspace (root) access to all
1941           io-memory regardless of whether a driver is actively using that
1942           range.  Accidental access to this is obviously disastrous, but
1943           specific access can be used by people debugging kernel drivers.
1944 
1945           If this option is switched on, the /dev/mem file only allows
1946           userspace access to *idle* io-memory ranges (see /proc/iomem) This
1947           may break traditional users of /dev/mem (dosemu, legacy X, etc...)
1948           if the driver using a given range cannot be disabled.
1949 
1950           If in doubt, say Y.

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