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1 | /* |
2 | * linux/fs/file.c |
3 | * |
4 | * Copyright (C) 1998-1999, Stephen Tweedie and Bill Hawes |
5 | * |
6 | * Manage the dynamic fd arrays in the process files_struct. |
7 | */ |
8 | |
9 | #include <linux/export.h> |
10 | #include <linux/fs.h> |
11 | #include <linux/mm.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> |
24 | |
25 | struct fdtable_defer { |
26 | spinlock_t lock; |
27 | struct work_struct wq; |
28 | struct fdtable *next; |
29 | }; |
30 | |
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 */ |
34 | |
35 | /* |
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. |
40 | */ |
41 | static DEFINE_PER_CPU(struct fdtable_defer, fdtable_defer_list); |
42 | |
43 | static void *alloc_fdmem(size_t size) |
44 | { |
45 | /* |
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. |
48 | */ |
49 | if (size <= (PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER)) { |
50 | void *data = kmalloc(size, GFP_KERNEL|__GFP_NOWARN); |
51 | if (data != NULL) |
52 | return data; |
53 | } |
54 | return vmalloc(size); |
55 | } |
56 | |
57 | static void free_fdmem(void *ptr) |
58 | { |
59 | is_vmalloc_addr(ptr) ? vfree(ptr) : kfree(ptr); |
60 | } |
61 | |
62 | static void __free_fdtable(struct fdtable *fdt) |
63 | { |
64 | free_fdmem(fdt->fd); |
65 | free_fdmem(fdt->open_fds); |
66 | kfree(fdt); |
67 | } |
68 | |
69 | static void free_fdtable_work(struct work_struct *work) |
70 | { |
71 | struct fdtable_defer *f = |
72 | container_of(work, struct fdtable_defer, wq); |
73 | struct fdtable *fdt; |
74 | |
75 | spin_lock_bh(&f->lock); |
76 | fdt = f->next; |
77 | f->next = NULL; |
78 | spin_unlock_bh(&f->lock); |
79 | while(fdt) { |
80 | struct fdtable *next = fdt->next; |
81 | |
82 | __free_fdtable(fdt); |
83 | fdt = next; |
84 | } |
85 | } |
86 | |
87 | void free_fdtable_rcu(struct rcu_head *rcu) |
88 | { |
89 | struct fdtable *fdt = container_of(rcu, struct fdtable, rcu); |
90 | struct fdtable_defer *fddef; |
91 | |
92 | BUG_ON(!fdt); |
93 | |
94 | if (fdt->max_fds <= NR_OPEN_DEFAULT) { |
95 | /* |
96 | * This fdtable is embedded in the files structure and that |
97 | * structure itself is getting destroyed. |
98 | */ |
99 | kmem_cache_free(files_cachep, |
100 | container_of(fdt, struct files_struct, fdtab)); |
101 | return; |
102 | } |
103 | if (!is_vmalloc_addr(fdt->fd) && !is_vmalloc_addr(fdt->open_fds)) { |
104 | kfree(fdt->fd); |
105 | kfree(fdt->open_fds); |
106 | kfree(fdt); |
107 | } else { |
108 | fddef = &get_cpu_var(fdtable_defer_list); |
109 | spin_lock(&fddef->lock); |
110 | fdt->next = fddef->next; |
111 | fddef->next = fdt; |
112 | /* vmallocs are handled from the workqueue context */ |
113 | schedule_work(&fddef->wq); |
114 | spin_unlock(&fddef->lock); |
115 | put_cpu_var(fdtable_defer_list); |
116 | } |
117 | } |
118 | |
119 | /* |
120 | * Expand the fdset in the files_struct. Called with the files spinlock |
121 | * held for write. |
122 | */ |
123 | static void copy_fdtable(struct fdtable *nfdt, struct fdtable *ofdt) |
124 | { |
125 | unsigned int cpy, set; |
126 | |
127 | BUG_ON(nfdt->max_fds < ofdt->max_fds); |
128 | |
129 | cpy = ofdt->max_fds * sizeof(struct file *); |
130 | set = (nfdt->max_fds - ofdt->max_fds) * sizeof(struct file *); |
131 | memcpy(nfdt->fd, ofdt->fd, cpy); |
132 | memset((char *)(nfdt->fd) + cpy, 0, set); |
133 | |
134 | cpy = ofdt->max_fds / BITS_PER_BYTE; |
135 | set = (nfdt->max_fds - ofdt->max_fds) / BITS_PER_BYTE; |
136 | memcpy(nfdt->open_fds, ofdt->open_fds, cpy); |
137 | memset((char *)(nfdt->open_fds) + cpy, 0, set); |
138 | memcpy(nfdt->close_on_exec, ofdt->close_on_exec, cpy); |
139 | memset((char *)(nfdt->close_on_exec) + cpy, 0, set); |
140 | } |
141 | |
142 | static struct fdtable * alloc_fdtable(unsigned int nr) |
143 | { |
144 | struct fdtable *fdt; |
145 | void *data; |
146 | |
147 | /* |
148 | * Figure out how many fds we actually want to support in this fdtable. |
149 | * Allocation steps are keyed to the size of the fdarray, since it |
150 | * grows far faster than any of the other dynamic data. We try to fit |
151 | * the fdarray into comfortable page-tuned chunks: starting at 1024B |
152 | * and growing in powers of two from there on. |
153 | */ |
154 | nr /= (1024 / sizeof(struct file *)); |
155 | nr = roundup_pow_of_two(nr + 1); |
156 | nr *= (1024 / sizeof(struct file *)); |
157 | /* |
158 | * Note that this can drive nr *below* what we had passed if sysctl_nr_open |
159 | * had been set lower between the check in expand_files() and here. Deal |
160 | * with that in caller, it's cheaper that way. |
161 | * |
162 | * We make sure that nr remains a multiple of BITS_PER_LONG - otherwise |
163 | * bitmaps handling below becomes unpleasant, to put it mildly... |
164 | */ |
165 | if (unlikely(nr > sysctl_nr_open)) |
166 | nr = ((sysctl_nr_open - 1) | (BITS_PER_LONG - 1)) + 1; |
167 | |
168 | fdt = kmalloc(sizeof(struct fdtable), GFP_KERNEL); |
169 | if (!fdt) |
170 | goto out; |
171 | fdt->max_fds = nr; |
172 | data = alloc_fdmem(nr * sizeof(struct file *)); |
173 | if (!data) |
174 | goto out_fdt; |
175 | fdt->fd = data; |
176 | |
177 | data = alloc_fdmem(max_t(size_t, |
178 | 2 * nr / BITS_PER_BYTE, L1_CACHE_BYTES)); |
179 | if (!data) |
180 | goto out_arr; |
181 | fdt->open_fds = data; |
182 | data += nr / BITS_PER_BYTE; |
183 | fdt->close_on_exec = data; |
184 | fdt->next = NULL; |
185 | |
186 | return fdt; |
187 | |
188 | out_arr: |
189 | free_fdmem(fdt->fd); |
190 | out_fdt: |
191 | kfree(fdt); |
192 | out: |
193 | return NULL; |
194 | } |
195 | |
196 | /* |
197 | * Expand the file descriptor table. |
198 | * This function will allocate a new fdtable and both fd array and fdset, of |
199 | * the given size. |
200 | * Return <0 error code on error; 1 on successful completion. |
201 | * The files->file_lock should be held on entry, and will be held on exit. |
202 | */ |
203 | static int expand_fdtable(struct files_struct *files, int nr) |
204 | __releases(files->file_lock) |
205 | __acquires(files->file_lock) |
206 | { |
207 | struct fdtable *new_fdt, *cur_fdt; |
208 | |
209 | spin_unlock(&files->file_lock); |
210 | new_fdt = alloc_fdtable(nr); |
211 | spin_lock(&files->file_lock); |
212 | if (!new_fdt) |
213 | return -ENOMEM; |
214 | /* |
215 | * extremely unlikely race - sysctl_nr_open decreased between the check in |
216 | * caller and alloc_fdtable(). Cheaper to catch it here... |
217 | */ |
218 | if (unlikely(new_fdt->max_fds <= nr)) { |
219 | __free_fdtable(new_fdt); |
220 | return -EMFILE; |
221 | } |
222 | /* |
223 | * Check again since another task may have expanded the fd table while |
224 | * we dropped the lock |
225 | */ |
226 | cur_fdt = files_fdtable(files); |
227 | if (nr >= cur_fdt->max_fds) { |
228 | /* Continue as planned */ |
229 | copy_fdtable(new_fdt, cur_fdt); |
230 | rcu_assign_pointer(files->fdt, new_fdt); |
231 | if (cur_fdt->max_fds > NR_OPEN_DEFAULT) |
232 | free_fdtable(cur_fdt); |
233 | } else { |
234 | /* Somebody else expanded, so undo our attempt */ |
235 | __free_fdtable(new_fdt); |
236 | } |
237 | return 1; |
238 | } |
239 | |
240 | /* |
241 | * Expand files. |
242 | * This function will expand the file structures, if the requested size exceeds |
243 | * the current capacity and there is room for expansion. |
244 | * Return <0 error code on error; 0 when nothing done; 1 when files were |
245 | * expanded and execution may have blocked. |
246 | * The files->file_lock should be held on entry, and will be held on exit. |
247 | */ |
248 | int expand_files(struct files_struct *files, int nr) |
249 | { |
250 | struct fdtable *fdt; |
251 | |
252 | fdt = files_fdtable(files); |
253 | |
254 | /* |
255 | * N.B. For clone tasks sharing a files structure, this test |
256 | * will limit the total number of files that can be opened. |
257 | */ |
258 | if (nr >= rlimit(RLIMIT_NOFILE)) |
259 | return -EMFILE; |
260 | |
261 | /* Do we need to expand? */ |
262 | if (nr < fdt->max_fds) |
263 | return 0; |
264 | |
265 | /* Can we expand? */ |
266 | if (nr >= sysctl_nr_open) |
267 | return -EMFILE; |
268 | |
269 | /* All good, so we try */ |
270 | return expand_fdtable(files, nr); |
271 | } |
272 | |
273 | static int count_open_files(struct fdtable *fdt) |
274 | { |
275 | int size = fdt->max_fds; |
276 | int i; |
277 | |
278 | /* Find the last open fd */ |
279 | for (i = size / BITS_PER_LONG; i > 0; ) { |
280 | if (fdt->open_fds[--i]) |
281 | break; |
282 | } |
283 | i = (i + 1) * BITS_PER_LONG; |
284 | return i; |
285 | } |
286 | |
287 | /* |
288 | * Allocate a new files structure and copy contents from the |
289 | * passed in files structure. |
290 | * errorp will be valid only when the returned files_struct is NULL. |
291 | */ |
292 | struct files_struct *dup_fd(struct files_struct *oldf, int *errorp) |
293 | { |
294 | struct files_struct *newf; |
295 | struct file **old_fds, **new_fds; |
296 | int open_files, size, i; |
297 | struct fdtable *old_fdt, *new_fdt; |
298 | |
299 | *errorp = -ENOMEM; |
300 | newf = kmem_cache_alloc(files_cachep, GFP_KERNEL); |
301 | if (!newf) |
302 | goto out; |
303 | |
304 | atomic_set(&newf->count, 1); |
305 | |
306 | spin_lock_init(&newf->file_lock); |
307 | newf->next_fd = 0; |
308 | new_fdt = &newf->fdtab; |
309 | new_fdt->max_fds = NR_OPEN_DEFAULT; |
310 | new_fdt->close_on_exec = newf->close_on_exec_init; |
311 | new_fdt->open_fds = newf->open_fds_init; |
312 | new_fdt->fd = &newf->fd_array[0]; |
313 | new_fdt->next = NULL; |
314 | |
315 | spin_lock(&oldf->file_lock); |
316 | old_fdt = files_fdtable(oldf); |
317 | open_files = count_open_files(old_fdt); |
318 | |
319 | /* |
320 | * Check whether we need to allocate a larger fd array and fd set. |
321 | */ |
322 | while (unlikely(open_files > new_fdt->max_fds)) { |
323 | spin_unlock(&oldf->file_lock); |
324 | |
325 | if (new_fdt != &newf->fdtab) |
326 | __free_fdtable(new_fdt); |
327 | |
328 | new_fdt = alloc_fdtable(open_files - 1); |
329 | if (!new_fdt) { |
330 | *errorp = -ENOMEM; |
331 | goto out_release; |
332 | } |
333 | |
334 | /* beyond sysctl_nr_open; nothing to do */ |
335 | if (unlikely(new_fdt->max_fds < open_files)) { |
336 | __free_fdtable(new_fdt); |
337 | *errorp = -EMFILE; |
338 | goto out_release; |
339 | } |
340 | |
341 | /* |
342 | * Reacquire the oldf lock and a pointer to its fd table |
343 | * who knows it may have a new bigger fd table. We need |
344 | * the latest pointer. |
345 | */ |
346 | spin_lock(&oldf->file_lock); |
347 | old_fdt = files_fdtable(oldf); |
348 | open_files = count_open_files(old_fdt); |
349 | } |
350 | |
351 | old_fds = old_fdt->fd; |
352 | new_fds = new_fdt->fd; |
353 | |
354 | memcpy(new_fdt->open_fds, old_fdt->open_fds, open_files / 8); |
355 | memcpy(new_fdt->close_on_exec, old_fdt->close_on_exec, open_files / 8); |
356 | |
357 | for (i = open_files; i != 0; i--) { |
358 | struct file *f = *old_fds++; |
359 | if (f) { |
360 | get_file(f); |
361 | } else { |
362 | /* |
363 | * The fd may be claimed in the fd bitmap but not yet |
364 | * instantiated in the files array if a sibling thread |
365 | * is partway through open(). So make sure that this |
366 | * fd is available to the new process. |
367 | */ |
368 | __clear_open_fd(open_files - i, new_fdt); |
369 | } |
370 | rcu_assign_pointer(*new_fds++, f); |
371 | } |
372 | spin_unlock(&oldf->file_lock); |
373 | |
374 | /* compute the remainder to be cleared */ |
375 | size = (new_fdt->max_fds - open_files) * sizeof(struct file *); |
376 | |
377 | /* This is long word aligned thus could use a optimized version */ |
378 | memset(new_fds, 0, size); |
379 | |
380 | if (new_fdt->max_fds > open_files) { |
381 | int left = (new_fdt->max_fds - open_files) / 8; |
382 | int start = open_files / BITS_PER_LONG; |
383 | |
384 | memset(&new_fdt->open_fds[start], 0, left); |
385 | memset(&new_fdt->close_on_exec[start], 0, left); |
386 | } |
387 | |
388 | rcu_assign_pointer(newf->fdt, new_fdt); |
389 | |
390 | return newf; |
391 | |
392 | out_release: |
393 | kmem_cache_free(files_cachep, newf); |
394 | out: |
395 | return NULL; |
396 | } |
397 | |
398 | static void __devinit fdtable_defer_list_init(int cpu) |
399 | { |
400 | struct fdtable_defer *fddef = &per_cpu(fdtable_defer_list, cpu); |
401 | spin_lock_init(&fddef->lock); |
402 | INIT_WORK(&fddef->wq, free_fdtable_work); |
403 | fddef->next = NULL; |
404 | } |
405 | |
406 | void __init files_defer_init(void) |
407 | { |
408 | int i; |
409 | for_each_possible_cpu(i) |
410 | fdtable_defer_list_init(i); |
411 | sysctl_nr_open_max = min((size_t)INT_MAX, ~(size_t)0/sizeof(void *)) & |
412 | -BITS_PER_LONG; |
413 | } |
414 | |
415 | struct files_struct init_files = { |
416 | .count = ATOMIC_INIT(1), |
417 | .fdt = &init_files.fdtab, |
418 | .fdtab = { |
419 | .max_fds = NR_OPEN_DEFAULT, |
420 | .fd = &init_files.fd_array[0], |
421 | .close_on_exec = init_files.close_on_exec_init, |
422 | .open_fds = init_files.open_fds_init, |
423 | }, |
424 | .file_lock = __SPIN_LOCK_UNLOCKED(init_task.file_lock), |
425 | }; |
426 | |
427 | /* |
428 | * allocate a file descriptor, mark it busy. |
429 | */ |
430 | int alloc_fd(unsigned start, unsigned flags) |
431 | { |
432 | struct files_struct *files = current->files; |
433 | unsigned int fd; |
434 | int error; |
435 | struct fdtable *fdt; |
436 | |
437 | spin_lock(&files->file_lock); |
438 | repeat: |
439 | fdt = files_fdtable(files); |
440 | fd = start; |
441 | if (fd < files->next_fd) |
442 | fd = files->next_fd; |
443 | |
444 | if (fd < fdt->max_fds) |
445 | fd = find_next_zero_bit(fdt->open_fds, fdt->max_fds, fd); |
446 | |
447 | error = expand_files(files, fd); |
448 | if (error < 0) |
449 | goto out; |
450 | |
451 | /* |
452 | * If we needed to expand the fs array we |
453 | * might have blocked - try again. |
454 | */ |
455 | if (error) |
456 | goto repeat; |
457 | |
458 | if (start <= files->next_fd) |
459 | files->next_fd = fd + 1; |
460 | |
461 | __set_open_fd(fd, fdt); |
462 | if (flags & O_CLOEXEC) |
463 | __set_close_on_exec(fd, fdt); |
464 | else |
465 | __clear_close_on_exec(fd, fdt); |
466 | error = fd; |
467 | #if 1 |
468 | /* Sanity check */ |
469 | if (rcu_dereference_raw(fdt->fd[fd]) != NULL) { |
470 | printk(KERN_WARNING "alloc_fd: slot %d not NULL!\n", fd); |
471 | rcu_assign_pointer(fdt->fd[fd], NULL); |
472 | } |
473 | #endif |
474 | |
475 | out: |
476 | spin_unlock(&files->file_lock); |
477 | return error; |
478 | } |
479 | |
480 | int get_unused_fd(void) |
481 | { |
482 | return alloc_fd(0, 0); |
483 | } |
484 | EXPORT_SYMBOL(get_unused_fd); |
485 |
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