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Linux/fs/file_table.c

  1 /*
  2  *  linux/fs/file_table.c
  3  *
  4  *  Copyright (C) 1991, 1992  Linus Torvalds
  5  *  Copyright (C) 1997 David S. Miller (davem@caip.rutgers.edu)
  6  */
  7 
  8 #include <linux/string.h>
  9 #include <linux/slab.h>
 10 #include <linux/file.h>
 11 #include <linux/fdtable.h>
 12 #include <linux/init.h>
 13 #include <linux/module.h>
 14 #include <linux/fs.h>
 15 #include <linux/security.h>
 16 #include <linux/eventpoll.h>
 17 #include <linux/rcupdate.h>
 18 #include <linux/mount.h>
 19 #include <linux/capability.h>
 20 #include <linux/cdev.h>
 21 #include <linux/fsnotify.h>
 22 #include <linux/sysctl.h>
 23 #include <linux/percpu_counter.h>
 24 #include <linux/percpu.h>
 25 #include <linux/hardirq.h>
 26 #include <linux/task_work.h>
 27 #include <linux/ima.h>
 28 #include <linux/swap.h>
 29 
 30 #include <linux/atomic.h>
 31 
 32 #include "internal.h"
 33 
 34 /* sysctl tunables... */
 35 struct files_stat_struct files_stat = {
 36         .max_files = NR_FILE
 37 };
 38 
 39 /* SLAB cache for file structures */
 40 static struct kmem_cache *filp_cachep __read_mostly;
 41 
 42 static struct percpu_counter nr_files __cacheline_aligned_in_smp;
 43 
 44 static void file_free_rcu(struct rcu_head *head)
 45 {
 46         struct file *f = container_of(head, struct file, f_u.fu_rcuhead);
 47 
 48         put_cred(f->f_cred);
 49         kmem_cache_free(filp_cachep, f);
 50 }
 51 
 52 static inline void file_free(struct file *f)
 53 {
 54         percpu_counter_dec(&nr_files);
 55         call_rcu(&f->f_u.fu_rcuhead, file_free_rcu);
 56 }
 57 
 58 /*
 59  * Return the total number of open files in the system
 60  */
 61 static long get_nr_files(void)
 62 {
 63         return percpu_counter_read_positive(&nr_files);
 64 }
 65 
 66 /*
 67  * Return the maximum number of open files in the system
 68  */
 69 unsigned long get_max_files(void)
 70 {
 71         return files_stat.max_files;
 72 }
 73 EXPORT_SYMBOL_GPL(get_max_files);
 74 
 75 /*
 76  * Handle nr_files sysctl
 77  */
 78 #if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
 79 int proc_nr_files(struct ctl_table *table, int write,
 80                      void __user *buffer, size_t *lenp, loff_t *ppos)
 81 {
 82         files_stat.nr_files = get_nr_files();
 83         return proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
 84 }
 85 #else
 86 int proc_nr_files(struct ctl_table *table, int write,
 87                      void __user *buffer, size_t *lenp, loff_t *ppos)
 88 {
 89         return -ENOSYS;
 90 }
 91 #endif
 92 
 93 /* Find an unused file structure and return a pointer to it.
 94  * Returns an error pointer if some error happend e.g. we over file
 95  * structures limit, run out of memory or operation is not permitted.
 96  *
 97  * Be very careful using this.  You are responsible for
 98  * getting write access to any mount that you might assign
 99  * to this filp, if it is opened for write.  If this is not
100  * done, you will imbalance int the mount's writer count
101  * and a warning at __fput() time.
102  */
103 struct file *get_empty_filp(void)
104 {
105         const struct cred *cred = current_cred();
106         static long old_max;
107         struct file *f;
108         int error;
109 
110         /*
111          * Privileged users can go above max_files
112          */
113         if (get_nr_files() >= files_stat.max_files && !capable(CAP_SYS_ADMIN)) {
114                 /*
115                  * percpu_counters are inaccurate.  Do an expensive check before
116                  * we go and fail.
117                  */
118                 if (percpu_counter_sum_positive(&nr_files) >= files_stat.max_files)
119                         goto over;
120         }
121 
122         f = kmem_cache_zalloc(filp_cachep, GFP_KERNEL);
123         if (unlikely(!f))
124                 return ERR_PTR(-ENOMEM);
125 
126         percpu_counter_inc(&nr_files);
127         f->f_cred = get_cred(cred);
128         error = security_file_alloc(f);
129         if (unlikely(error)) {
130                 file_free(f);
131                 return ERR_PTR(error);
132         }
133 
134         atomic_long_set(&f->f_count, 1);
135         rwlock_init(&f->f_owner.lock);
136         spin_lock_init(&f->f_lock);
137         mutex_init(&f->f_pos_lock);
138         eventpoll_init_file(f);
139         /* f->f_version: 0 */
140         return f;
141 
142 over:
143         /* Ran out of filps - report that */
144         if (get_nr_files() > old_max) {
145                 pr_info("VFS: file-max limit %lu reached\n", get_max_files());
146                 old_max = get_nr_files();
147         }
148         return ERR_PTR(-ENFILE);
149 }
150 
151 /**
152  * alloc_file - allocate and initialize a 'struct file'
153  *
154  * @path: the (dentry, vfsmount) pair for the new file
155  * @mode: the mode with which the new file will be opened
156  * @fop: the 'struct file_operations' for the new file
157  */
158 struct file *alloc_file(const struct path *path, fmode_t mode,
159                 const struct file_operations *fop)
160 {
161         struct file *file;
162 
163         file = get_empty_filp();
164         if (IS_ERR(file))
165                 return file;
166 
167         file->f_path = *path;
168         file->f_inode = path->dentry->d_inode;
169         file->f_mapping = path->dentry->d_inode->i_mapping;
170         if ((mode & FMODE_READ) &&
171              likely(fop->read || fop->read_iter))
172                 mode |= FMODE_CAN_READ;
173         if ((mode & FMODE_WRITE) &&
174              likely(fop->write || fop->write_iter))
175                 mode |= FMODE_CAN_WRITE;
176         file->f_mode = mode;
177         file->f_op = fop;
178         if ((mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
179                 i_readcount_inc(path->dentry->d_inode);
180         return file;
181 }
182 EXPORT_SYMBOL(alloc_file);
183 
184 /* the real guts of fput() - releasing the last reference to file
185  */
186 static void __fput(struct file *file)
187 {
188         struct dentry *dentry = file->f_path.dentry;
189         struct vfsmount *mnt = file->f_path.mnt;
190         struct inode *inode = file->f_inode;
191 
192         might_sleep();
193 
194         fsnotify_close(file);
195         /*
196          * The function eventpoll_release() should be the first called
197          * in the file cleanup chain.
198          */
199         eventpoll_release(file);
200         locks_remove_file(file);
201 
202         if (unlikely(file->f_flags & FASYNC)) {
203                 if (file->f_op->fasync)
204                         file->f_op->fasync(-1, file, 0);
205         }
206         ima_file_free(file);
207         if (file->f_op->release)
208                 file->f_op->release(inode, file);
209         security_file_free(file);
210         if (unlikely(S_ISCHR(inode->i_mode) && inode->i_cdev != NULL &&
211                      !(file->f_mode & FMODE_PATH))) {
212                 cdev_put(inode->i_cdev);
213         }
214         fops_put(file->f_op);
215         put_pid(file->f_owner.pid);
216         if ((file->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
217                 i_readcount_dec(inode);
218         if (file->f_mode & FMODE_WRITER) {
219                 put_write_access(inode);
220                 __mnt_drop_write(mnt);
221         }
222         file->f_path.dentry = NULL;
223         file->f_path.mnt = NULL;
224         file->f_inode = NULL;
225         file_free(file);
226         dput(dentry);
227         mntput(mnt);
228 }
229 
230 static LLIST_HEAD(delayed_fput_list);
231 static void delayed_fput(struct work_struct *unused)
232 {
233         struct llist_node *node = llist_del_all(&delayed_fput_list);
234         struct llist_node *next;
235 
236         for (; node; node = next) {
237                 next = llist_next(node);
238                 __fput(llist_entry(node, struct file, f_u.fu_llist));
239         }
240 }
241 
242 static void ____fput(struct callback_head *work)
243 {
244         __fput(container_of(work, struct file, f_u.fu_rcuhead));
245 }
246 
247 /*
248  * If kernel thread really needs to have the final fput() it has done
249  * to complete, call this.  The only user right now is the boot - we
250  * *do* need to make sure our writes to binaries on initramfs has
251  * not left us with opened struct file waiting for __fput() - execve()
252  * won't work without that.  Please, don't add more callers without
253  * very good reasons; in particular, never call that with locks
254  * held and never call that from a thread that might need to do
255  * some work on any kind of umount.
256  */
257 void flush_delayed_fput(void)
258 {
259         delayed_fput(NULL);
260 }
261 
262 static DECLARE_DELAYED_WORK(delayed_fput_work, delayed_fput);
263 
264 void fput(struct file *file)
265 {
266         if (atomic_long_dec_and_test(&file->f_count)) {
267                 struct task_struct *task = current;
268 
269                 if (likely(!in_interrupt() && !(task->flags & PF_KTHREAD))) {
270                         init_task_work(&file->f_u.fu_rcuhead, ____fput);
271                         if (!task_work_add(task, &file->f_u.fu_rcuhead, true))
272                                 return;
273                         /*
274                          * After this task has run exit_task_work(),
275                          * task_work_add() will fail.  Fall through to delayed
276                          * fput to avoid leaking *file.
277                          */
278                 }
279 
280                 if (llist_add(&file->f_u.fu_llist, &delayed_fput_list))
281                         schedule_delayed_work(&delayed_fput_work, 1);
282         }
283 }
284 
285 /*
286  * synchronous analog of fput(); for kernel threads that might be needed
287  * in some umount() (and thus can't use flush_delayed_fput() without
288  * risking deadlocks), need to wait for completion of __fput() and know
289  * for this specific struct file it won't involve anything that would
290  * need them.  Use only if you really need it - at the very least,
291  * don't blindly convert fput() by kernel thread to that.
292  */
293 void __fput_sync(struct file *file)
294 {
295         if (atomic_long_dec_and_test(&file->f_count)) {
296                 struct task_struct *task = current;
297                 BUG_ON(!(task->flags & PF_KTHREAD));
298                 __fput(file);
299         }
300 }
301 
302 EXPORT_SYMBOL(fput);
303 
304 void put_filp(struct file *file)
305 {
306         if (atomic_long_dec_and_test(&file->f_count)) {
307                 security_file_free(file);
308                 file_free(file);
309         }
310 }
311 
312 void __init files_init(void)
313 { 
314         filp_cachep = kmem_cache_create("filp", sizeof(struct file), 0,
315                         SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
316         percpu_counter_init(&nr_files, 0, GFP_KERNEL);
317 }
318 
319 /*
320  * One file with associated inode and dcache is very roughly 1K. Per default
321  * do not use more than 10% of our memory for files.
322  */
323 void __init files_maxfiles_init(void)
324 {
325         unsigned long n;
326         unsigned long memreserve = (totalram_pages - nr_free_pages()) * 3/2;
327 
328         memreserve = min(memreserve, totalram_pages - 1);
329         n = ((totalram_pages - memreserve) * (PAGE_SIZE / 1024)) / 10;
330 
331         files_stat.max_files = max_t(unsigned long, n, NR_FILE);
332 } 
333 

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