4 * Copyright (C) 1998-1999, Stephen Tweedie and Bill Hawes
6 * Manage the dynamic fd arrays in the process files_struct.
9 #include <linux/export.h>
12 #include <linux/mmzone.h>
13 #include <linux/time.h>
14 #include <linux/sched.h>
15 #include <linux/slab.h>
16 #include <linux/vmalloc.h>
17 #include <linux/file.h>
18 #include <linux/fdtable.h>
19 #include <linux/bitops.h>
20 #include <linux/interrupt.h>
21 #include <linux/spinlock.h>
22 #include <linux/rcupdate.h>
23 #include <linux/workqueue.h>
25 struct fdtable_defer {
27 struct work_struct wq;
31 int sysctl_nr_open __read_mostly = 1024*1024;
32 int sysctl_nr_open_min = BITS_PER_LONG;
33 int sysctl_nr_open_max = 1024 * 1024; /* raised later */
36 * We use this list to defer free fdtables that have vmalloced
37 * sets/arrays. By keeping a per-cpu list, we avoid having to embed
38 * the work_struct in fdtable itself which avoids a 64 byte (i386) increase in
39 * this per-task structure.
41 static DEFINE_PER_CPU(struct fdtable_defer, fdtable_defer_list);
43 static void *alloc_fdmem(size_t size)
46 * Very large allocations can stress page reclaim, so fall back to
47 * vmalloc() if the allocation size will be considered "large" by the VM.
49 if (size <= (PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER)) {
50 void *data = kmalloc(size, GFP_KERNEL|__GFP_NOWARN);
57 static void free_fdmem(void *ptr)
59 is_vmalloc_addr(ptr) ? vfree(ptr) : kfree(ptr);
62 static void __free_fdtable(struct fdtable *fdt)
65 free_fdmem(fdt->open_fds);
69 static void free_fdtable_work(struct work_struct *work)
71 struct fdtable_defer *f =
72 container_of(work, struct fdtable_defer, wq);
75 spin_lock_bh(&f->lock);
78 spin_unlock_bh(&f->lock);
80 struct fdtable *next = fdt->next;
87 static void free_fdtable_rcu(struct rcu_head *rcu)
89 struct fdtable *fdt = container_of(rcu, struct fdtable, rcu);
90 struct fdtable_defer *fddef;
93 BUG_ON(fdt->max_fds <= NR_OPEN_DEFAULT);
95 if (!is_vmalloc_addr(fdt->fd) && !is_vmalloc_addr(fdt->open_fds)) {
100 fddef = &get_cpu_var(fdtable_defer_list);
101 spin_lock(&fddef->lock);
102 fdt->next = fddef->next;
104 /* vmallocs are handled from the workqueue context */
105 schedule_work(&fddef->wq);
106 spin_unlock(&fddef->lock);
107 put_cpu_var(fdtable_defer_list);
112 * Expand the fdset in the files_struct. Called with the files spinlock
115 static void copy_fdtable(struct fdtable *nfdt, struct fdtable *ofdt)
117 unsigned int cpy, set;
119 BUG_ON(nfdt->max_fds < ofdt->max_fds);
121 cpy = ofdt->max_fds * sizeof(struct file *);
122 set = (nfdt->max_fds - ofdt->max_fds) * sizeof(struct file *);
123 memcpy(nfdt->fd, ofdt->fd, cpy);
124 memset((char *)(nfdt->fd) + cpy, 0, set);
126 cpy = ofdt->max_fds / BITS_PER_BYTE;
127 set = (nfdt->max_fds - ofdt->max_fds) / BITS_PER_BYTE;
128 memcpy(nfdt->open_fds, ofdt->open_fds, cpy);
129 memset((char *)(nfdt->open_fds) + cpy, 0, set);
130 memcpy(nfdt->close_on_exec, ofdt->close_on_exec, cpy);
131 memset((char *)(nfdt->close_on_exec) + cpy, 0, set);
134 static struct fdtable * alloc_fdtable(unsigned int nr)
140 * Figure out how many fds we actually want to support in this fdtable.
141 * Allocation steps are keyed to the size of the fdarray, since it
142 * grows far faster than any of the other dynamic data. We try to fit
143 * the fdarray into comfortable page-tuned chunks: starting at 1024B
144 * and growing in powers of two from there on.
146 nr /= (1024 / sizeof(struct file *));
147 nr = roundup_pow_of_two(nr + 1);
148 nr *= (1024 / sizeof(struct file *));
150 * Note that this can drive nr *below* what we had passed if sysctl_nr_open
151 * had been set lower between the check in expand_files() and here. Deal
152 * with that in caller, it's cheaper that way.
154 * We make sure that nr remains a multiple of BITS_PER_LONG - otherwise
155 * bitmaps handling below becomes unpleasant, to put it mildly...
157 if (unlikely(nr > sysctl_nr_open))
158 nr = ((sysctl_nr_open - 1) | (BITS_PER_LONG - 1)) + 1;
160 fdt = kmalloc(sizeof(struct fdtable), GFP_KERNEL);
164 data = alloc_fdmem(nr * sizeof(struct file *));
169 data = alloc_fdmem(max_t(size_t,
170 2 * nr / BITS_PER_BYTE, L1_CACHE_BYTES));
173 fdt->open_fds = data;
174 data += nr / BITS_PER_BYTE;
175 fdt->close_on_exec = data;
189 * Expand the file descriptor table.
190 * This function will allocate a new fdtable and both fd array and fdset, of
192 * Return <0 error code on error; 1 on successful completion.
193 * The files->file_lock should be held on entry, and will be held on exit.
195 static int expand_fdtable(struct files_struct *files, int nr)
196 __releases(files->file_lock)
197 __acquires(files->file_lock)
199 struct fdtable *new_fdt, *cur_fdt;
201 spin_unlock(&files->file_lock);
202 new_fdt = alloc_fdtable(nr);
203 spin_lock(&files->file_lock);
207 * extremely unlikely race - sysctl_nr_open decreased between the check in
208 * caller and alloc_fdtable(). Cheaper to catch it here...
210 if (unlikely(new_fdt->max_fds <= nr)) {
211 __free_fdtable(new_fdt);
215 * Check again since another task may have expanded the fd table while
216 * we dropped the lock
218 cur_fdt = files_fdtable(files);
219 if (nr >= cur_fdt->max_fds) {
220 /* Continue as planned */
221 copy_fdtable(new_fdt, cur_fdt);
222 rcu_assign_pointer(files->fdt, new_fdt);
223 if (cur_fdt->max_fds > NR_OPEN_DEFAULT)
224 call_rcu(&cur_fdt->rcu, free_fdtable_rcu);
226 /* Somebody else expanded, so undo our attempt */
227 __free_fdtable(new_fdt);
234 * This function will expand the file structures, if the requested size exceeds
235 * the current capacity and there is room for expansion.
236 * Return <0 error code on error; 0 when nothing done; 1 when files were
237 * expanded and execution may have blocked.
238 * The files->file_lock should be held on entry, and will be held on exit.
240 int expand_files(struct files_struct *files, int nr)
244 fdt = files_fdtable(files);
246 /* Do we need to expand? */
247 if (nr < fdt->max_fds)
251 if (nr >= sysctl_nr_open)
254 /* All good, so we try */
255 return expand_fdtable(files, nr);
258 static int count_open_files(struct fdtable *fdt)
260 int size = fdt->max_fds;
263 /* Find the last open fd */
264 for (i = size / BITS_PER_LONG; i > 0; ) {
265 if (fdt->open_fds[--i])
268 i = (i + 1) * BITS_PER_LONG;
273 * Allocate a new files structure and copy contents from the
274 * passed in files structure.
275 * errorp will be valid only when the returned files_struct is NULL.
277 struct files_struct *dup_fd(struct files_struct *oldf, int *errorp)
279 struct files_struct *newf;
280 struct file **old_fds, **new_fds;
281 int open_files, size, i;
282 struct fdtable *old_fdt, *new_fdt;
285 newf = kmem_cache_alloc(files_cachep, GFP_KERNEL);
289 atomic_set(&newf->count, 1);
291 spin_lock_init(&newf->file_lock);
293 new_fdt = &newf->fdtab;
294 new_fdt->max_fds = NR_OPEN_DEFAULT;
295 new_fdt->close_on_exec = newf->close_on_exec_init;
296 new_fdt->open_fds = newf->open_fds_init;
297 new_fdt->fd = &newf->fd_array[0];
298 new_fdt->next = NULL;
300 spin_lock(&oldf->file_lock);
301 old_fdt = files_fdtable(oldf);
302 open_files = count_open_files(old_fdt);
305 * Check whether we need to allocate a larger fd array and fd set.
307 while (unlikely(open_files > new_fdt->max_fds)) {
308 spin_unlock(&oldf->file_lock);
310 if (new_fdt != &newf->fdtab)
311 __free_fdtable(new_fdt);
313 new_fdt = alloc_fdtable(open_files - 1);
319 /* beyond sysctl_nr_open; nothing to do */
320 if (unlikely(new_fdt->max_fds < open_files)) {
321 __free_fdtable(new_fdt);
327 * Reacquire the oldf lock and a pointer to its fd table
328 * who knows it may have a new bigger fd table. We need
329 * the latest pointer.
331 spin_lock(&oldf->file_lock);
332 old_fdt = files_fdtable(oldf);
333 open_files = count_open_files(old_fdt);
336 old_fds = old_fdt->fd;
337 new_fds = new_fdt->fd;
339 memcpy(new_fdt->open_fds, old_fdt->open_fds, open_files / 8);
340 memcpy(new_fdt->close_on_exec, old_fdt->close_on_exec, open_files / 8);
342 for (i = open_files; i != 0; i--) {
343 struct file *f = *old_fds++;
348 * The fd may be claimed in the fd bitmap but not yet
349 * instantiated in the files array if a sibling thread
350 * is partway through open(). So make sure that this
351 * fd is available to the new process.
353 __clear_open_fd(open_files - i, new_fdt);
355 rcu_assign_pointer(*new_fds++, f);
357 spin_unlock(&oldf->file_lock);
359 /* compute the remainder to be cleared */
360 size = (new_fdt->max_fds - open_files) * sizeof(struct file *);
362 /* This is long word aligned thus could use a optimized version */
363 memset(new_fds, 0, size);
365 if (new_fdt->max_fds > open_files) {
366 int left = (new_fdt->max_fds - open_files) / 8;
367 int start = open_files / BITS_PER_LONG;
369 memset(&new_fdt->open_fds[start], 0, left);
370 memset(&new_fdt->close_on_exec[start], 0, left);
373 rcu_assign_pointer(newf->fdt, new_fdt);
378 kmem_cache_free(files_cachep, newf);
383 static void close_files(struct files_struct * files)
391 * It is safe to dereference the fd table without RCU or
392 * ->file_lock because this is the last reference to the
393 * files structure. But use RCU to shut RCU-lockdep up.
396 fdt = files_fdtable(files);
400 i = j * BITS_PER_LONG;
401 if (i >= fdt->max_fds)
403 set = fdt->open_fds[j++];
406 struct file * file = xchg(&fdt->fd[i], NULL);
408 filp_close(file, files);
418 struct files_struct *get_files_struct(struct task_struct *task)
420 struct files_struct *files;
425 atomic_inc(&files->count);
431 void put_files_struct(struct files_struct *files)
435 if (atomic_dec_and_test(&files->count)) {
437 /* not really needed, since nobody can see us */
439 fdt = files_fdtable(files);
441 /* free the arrays if they are not embedded */
442 if (fdt != &files->fdtab)
444 kmem_cache_free(files_cachep, files);
448 void reset_files_struct(struct files_struct *files)
450 struct task_struct *tsk = current;
451 struct files_struct *old;
457 put_files_struct(old);
460 void exit_files(struct task_struct *tsk)
462 struct files_struct * files = tsk->files;
468 put_files_struct(files);
472 static void __devinit fdtable_defer_list_init(int cpu)
474 struct fdtable_defer *fddef = &per_cpu(fdtable_defer_list, cpu);
475 spin_lock_init(&fddef->lock);
476 INIT_WORK(&fddef->wq, free_fdtable_work);
480 void __init files_defer_init(void)
483 for_each_possible_cpu(i)
484 fdtable_defer_list_init(i);
485 sysctl_nr_open_max = min((size_t)INT_MAX, ~(size_t)0/sizeof(void *)) &
489 struct files_struct init_files = {
490 .count = ATOMIC_INIT(1),
491 .fdt = &init_files.fdtab,
493 .max_fds = NR_OPEN_DEFAULT,
494 .fd = &init_files.fd_array[0],
495 .close_on_exec = init_files.close_on_exec_init,
496 .open_fds = init_files.open_fds_init,
498 .file_lock = __SPIN_LOCK_UNLOCKED(init_task.file_lock),
502 * allocate a file descriptor, mark it busy.
504 int __alloc_fd(struct files_struct *files,
505 unsigned start, unsigned end, unsigned flags)
511 spin_lock(&files->file_lock);
513 fdt = files_fdtable(files);
515 if (fd < files->next_fd)
518 if (fd < fdt->max_fds)
519 fd = find_next_zero_bit(fdt->open_fds, fdt->max_fds, fd);
522 * N.B. For clone tasks sharing a files structure, this test
523 * will limit the total number of files that can be opened.
529 error = expand_files(files, fd);
534 * If we needed to expand the fs array we
535 * might have blocked - try again.
540 if (start <= files->next_fd)
541 files->next_fd = fd + 1;
543 __set_open_fd(fd, fdt);
544 if (flags & O_CLOEXEC)
545 __set_close_on_exec(fd, fdt);
547 __clear_close_on_exec(fd, fdt);
551 if (rcu_dereference_raw(fdt->fd[fd]) != NULL) {
552 printk(KERN_WARNING "alloc_fd: slot %d not NULL!\n", fd);
553 rcu_assign_pointer(fdt->fd[fd], NULL);
558 spin_unlock(&files->file_lock);
562 int alloc_fd(unsigned start, unsigned flags)
564 return __alloc_fd(current->files, start, rlimit(RLIMIT_NOFILE), flags);
567 int get_unused_fd_flags(unsigned flags)
569 return __alloc_fd(current->files, 0, rlimit(RLIMIT_NOFILE), flags);
571 EXPORT_SYMBOL(get_unused_fd_flags);
573 static void __put_unused_fd(struct files_struct *files, unsigned int fd)
575 struct fdtable *fdt = files_fdtable(files);
576 __clear_open_fd(fd, fdt);
577 if (fd < files->next_fd)
581 void put_unused_fd(unsigned int fd)
583 struct files_struct *files = current->files;
584 spin_lock(&files->file_lock);
585 __put_unused_fd(files, fd);
586 spin_unlock(&files->file_lock);
589 EXPORT_SYMBOL(put_unused_fd);
592 * Install a file pointer in the fd array.
594 * The VFS is full of places where we drop the files lock between
595 * setting the open_fds bitmap and installing the file in the file
596 * array. At any such point, we are vulnerable to a dup2() race
597 * installing a file in the array before us. We need to detect this and
598 * fput() the struct file we are about to overwrite in this case.
600 * It should never happen - if we allow dup2() do it, _really_ bad things
604 void fd_install(unsigned int fd, struct file *file)
606 struct files_struct *files = current->files;
608 spin_lock(&files->file_lock);
609 fdt = files_fdtable(files);
610 BUG_ON(fdt->fd[fd] != NULL);
611 rcu_assign_pointer(fdt->fd[fd], file);
612 spin_unlock(&files->file_lock);
615 EXPORT_SYMBOL(fd_install);