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/fs.h> 10 #include <linux/mm.h> 11 #include <linux/time.h> 12 #include <linux/slab.h> 13 #include <linux/vmalloc.h> 14 #include <linux/file.h> 15 #include <linux/fdtable.h> 16 #include <linux/bitops.h> 17 #include <linux/interrupt.h> 18 #include <linux/spinlock.h> 19 #include <linux/rcupdate.h> 20 #include <linux/workqueue.h> 21 22 struct fdtable_defer { 23 spinlock_t lock; 24 struct work_struct wq; 25 struct fdtable *next; 26 }; 27 28 int sysctl_nr_open __read_mostly = 1024*1024; 29 int sysctl_nr_open_min = BITS_PER_LONG; 30 int sysctl_nr_open_max = 1024 * 1024; /* raised later */ 31 32 /* 33 * We use this list to defer free fdtables that have vmalloced 34 * sets/arrays. By keeping a per-cpu list, we avoid having to embed 35 * the work_struct in fdtable itself which avoids a 64 byte (i386) increase in 36 * this per-task structure. 37 */ 38 static DEFINE_PER_CPU(struct fdtable_defer, fdtable_defer_list); 39 40 static inline void * alloc_fdmem(unsigned int size) 41 { 42 if (size <= PAGE_SIZE) 43 return kmalloc(size, GFP_KERNEL); 44 else 45 return vmalloc(size); 46 } 47 48 static inline void free_fdarr(struct fdtable *fdt) 49 { 50 if (fdt->max_fds <= (PAGE_SIZE / sizeof(struct file *))) 51 kfree(fdt->fd); 52 else 53 vfree(fdt->fd); 54 } 55 56 static inline void free_fdset(struct fdtable *fdt) 57 { 58 if (fdt->max_fds <= (PAGE_SIZE * BITS_PER_BYTE / 2)) 59 kfree(fdt->open_fds); 60 else 61 vfree(fdt->open_fds); 62 } 63 64 static void free_fdtable_work(struct work_struct *work) 65 { 66 struct fdtable_defer *f = 67 container_of(work, struct fdtable_defer, wq); 68 struct fdtable *fdt; 69 70 spin_lock_bh(&f->lock); 71 fdt = f->next; 72 f->next = NULL; 73 spin_unlock_bh(&f->lock); 74 while(fdt) { 75 struct fdtable *next = fdt->next; 76 vfree(fdt->fd); 77 free_fdset(fdt); 78 kfree(fdt); 79 fdt = next; 80 } 81 } 82 83 void free_fdtable_rcu(struct rcu_head *rcu) 84 { 85 struct fdtable *fdt = container_of(rcu, struct fdtable, rcu); 86 struct fdtable_defer *fddef; 87 88 BUG_ON(!fdt); 89 90 if (fdt->max_fds <= NR_OPEN_DEFAULT) { 91 /* 92 * This fdtable is embedded in the files structure and that 93 * structure itself is getting destroyed. 94 */ 95 kmem_cache_free(files_cachep, 96 container_of(fdt, struct files_struct, fdtab)); 97 return; 98 } 99 if (fdt->max_fds <= (PAGE_SIZE / sizeof(struct file *))) { 100 kfree(fdt->fd); 101 kfree(fdt->open_fds); 102 kfree(fdt); 103 } else { 104 fddef = &get_cpu_var(fdtable_defer_list); 105 spin_lock(&fddef->lock); 106 fdt->next = fddef->next; 107 fddef->next = fdt; 108 /* vmallocs are handled from the workqueue context */ 109 schedule_work(&fddef->wq); 110 spin_unlock(&fddef->lock); 111 put_cpu_var(fdtable_defer_list); 112 } 113 } 114 115 /* 116 * Expand the fdset in the files_struct. Called with the files spinlock 117 * held for write. 118 */ 119 static void copy_fdtable(struct fdtable *nfdt, struct fdtable *ofdt) 120 { 121 unsigned int cpy, set; 122 123 BUG_ON(nfdt->max_fds < ofdt->max_fds); 124 125 cpy = ofdt->max_fds * sizeof(struct file *); 126 set = (nfdt->max_fds - ofdt->max_fds) * sizeof(struct file *); 127 memcpy(nfdt->fd, ofdt->fd, cpy); 128 memset((char *)(nfdt->fd) + cpy, 0, set); 129 130 cpy = ofdt->max_fds / BITS_PER_BYTE; 131 set = (nfdt->max_fds - ofdt->max_fds) / BITS_PER_BYTE; 132 memcpy(nfdt->open_fds, ofdt->open_fds, cpy); 133 memset((char *)(nfdt->open_fds) + cpy, 0, set); 134 memcpy(nfdt->close_on_exec, ofdt->close_on_exec, cpy); 135 memset((char *)(nfdt->close_on_exec) + cpy, 0, set); 136 } 137 138 static struct fdtable * alloc_fdtable(unsigned int nr) 139 { 140 struct fdtable *fdt; 141 char *data; 142 143 /* 144 * Figure out how many fds we actually want to support in this fdtable. 145 * Allocation steps are keyed to the size of the fdarray, since it 146 * grows far faster than any of the other dynamic data. We try to fit 147 * the fdarray into comfortable page-tuned chunks: starting at 1024B 148 * and growing in powers of two from there on. 149 */ 150 nr /= (1024 / sizeof(struct file *)); 151 nr = roundup_pow_of_two(nr + 1); 152 nr *= (1024 / sizeof(struct file *)); 153 /* 154 * Note that this can drive nr *below* what we had passed if sysctl_nr_open 155 * had been set lower between the check in expand_files() and here. Deal 156 * with that in caller, it's cheaper that way. 157 * 158 * We make sure that nr remains a multiple of BITS_PER_LONG - otherwise 159 * bitmaps handling below becomes unpleasant, to put it mildly... 160 */ 161 if (unlikely(nr > sysctl_nr_open)) 162 nr = ((sysctl_nr_open - 1) | (BITS_PER_LONG - 1)) + 1; 163 164 fdt = kmalloc(sizeof(struct fdtable), GFP_KERNEL); 165 if (!fdt) 166 goto out; 167 fdt->max_fds = nr; 168 data = alloc_fdmem(nr * sizeof(struct file *)); 169 if (!data) 170 goto out_fdt; 171 fdt->fd = (struct file **)data; 172 data = alloc_fdmem(max_t(unsigned int, 173 2 * nr / BITS_PER_BYTE, L1_CACHE_BYTES)); 174 if (!data) 175 goto out_arr; 176 fdt->open_fds = (fd_set *)data; 177 data += nr / BITS_PER_BYTE; 178 fdt->close_on_exec = (fd_set *)data; 179 INIT_RCU_HEAD(&fdt->rcu); 180 fdt->next = NULL; 181 182 return fdt; 183 184 out_arr: 185 free_fdarr(fdt); 186 out_fdt: 187 kfree(fdt); 188 out: 189 return NULL; 190 } 191 192 /* 193 * Expand the file descriptor table. 194 * This function will allocate a new fdtable and both fd array and fdset, of 195 * the given size. 196 * Return <0 error code on error; 1 on successful completion. 197 * The files->file_lock should be held on entry, and will be held on exit. 198 */ 199 static int expand_fdtable(struct files_struct *files, int nr) 200 __releases(files->file_lock) 201 __acquires(files->file_lock) 202 { 203 struct fdtable *new_fdt, *cur_fdt; 204 205 spin_unlock(&files->file_lock); 206 new_fdt = alloc_fdtable(nr); 207 spin_lock(&files->file_lock); 208 if (!new_fdt) 209 return -ENOMEM; 210 /* 211 * extremely unlikely race - sysctl_nr_open decreased between the check in 212 * caller and alloc_fdtable(). Cheaper to catch it here... 213 */ 214 if (unlikely(new_fdt->max_fds <= nr)) { 215 free_fdarr(new_fdt); 216 free_fdset(new_fdt); 217 kfree(new_fdt); 218 return -EMFILE; 219 } 220 /* 221 * Check again since another task may have expanded the fd table while 222 * we dropped the lock 223 */ 224 cur_fdt = files_fdtable(files); 225 if (nr >= cur_fdt->max_fds) { 226 /* Continue as planned */ 227 copy_fdtable(new_fdt, cur_fdt); 228 rcu_assign_pointer(files->fdt, new_fdt); 229 if (cur_fdt->max_fds > NR_OPEN_DEFAULT) 230 free_fdtable(cur_fdt); 231 } else { 232 /* Somebody else expanded, so undo our attempt */ 233 free_fdarr(new_fdt); 234 free_fdset(new_fdt); 235 kfree(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 >= current->signal->rlim[RLIMIT_NOFILE].rlim_cur) 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/(8*sizeof(long)); i > 0; ) { 280 if (fdt->open_fds->fds_bits[--i]) 281 break; 282 } 283 i = (i+1) * 8 * sizeof(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 = (fd_set *)&newf->close_on_exec_init; 311 new_fdt->open_fds = (fd_set *)&newf->open_fds_init; 312 new_fdt->fd = &newf->fd_array[0]; 313 INIT_RCU_HEAD(&new_fdt->rcu); 314 new_fdt->next = NULL; 315 316 spin_lock(&oldf->file_lock); 317 old_fdt = files_fdtable(oldf); 318 open_files = count_open_files(old_fdt); 319 320 /* 321 * Check whether we need to allocate a larger fd array and fd set. 322 */ 323 while (unlikely(open_files > new_fdt->max_fds)) { 324 spin_unlock(&oldf->file_lock); 325 326 if (new_fdt != &newf->fdtab) { 327 free_fdarr(new_fdt); 328 free_fdset(new_fdt); 329 kfree(new_fdt); 330 } 331 332 new_fdt = alloc_fdtable(open_files - 1); 333 if (!new_fdt) { 334 *errorp = -ENOMEM; 335 goto out_release; 336 } 337 338 /* beyond sysctl_nr_open; nothing to do */ 339 if (unlikely(new_fdt->max_fds < open_files)) { 340 free_fdarr(new_fdt); 341 free_fdset(new_fdt); 342 kfree(new_fdt); 343 *errorp = -EMFILE; 344 goto out_release; 345 } 346 347 /* 348 * Reacquire the oldf lock and a pointer to its fd table 349 * who knows it may have a new bigger fd table. We need 350 * the latest pointer. 351 */ 352 spin_lock(&oldf->file_lock); 353 old_fdt = files_fdtable(oldf); 354 open_files = count_open_files(old_fdt); 355 } 356 357 old_fds = old_fdt->fd; 358 new_fds = new_fdt->fd; 359 360 memcpy(new_fdt->open_fds->fds_bits, 361 old_fdt->open_fds->fds_bits, open_files/8); 362 memcpy(new_fdt->close_on_exec->fds_bits, 363 old_fdt->close_on_exec->fds_bits, open_files/8); 364 365 for (i = open_files; i != 0; i--) { 366 struct file *f = *old_fds++; 367 if (f) { 368 get_file(f); 369 } else { 370 /* 371 * The fd may be claimed in the fd bitmap but not yet 372 * instantiated in the files array if a sibling thread 373 * is partway through open(). So make sure that this 374 * fd is available to the new process. 375 */ 376 FD_CLR(open_files - i, new_fdt->open_fds); 377 } 378 rcu_assign_pointer(*new_fds++, f); 379 } 380 spin_unlock(&oldf->file_lock); 381 382 /* compute the remainder to be cleared */ 383 size = (new_fdt->max_fds - open_files) * sizeof(struct file *); 384 385 /* This is long word aligned thus could use a optimized version */ 386 memset(new_fds, 0, size); 387 388 if (new_fdt->max_fds > open_files) { 389 int left = (new_fdt->max_fds-open_files)/8; 390 int start = open_files / (8 * sizeof(unsigned long)); 391 392 memset(&new_fdt->open_fds->fds_bits[start], 0, left); 393 memset(&new_fdt->close_on_exec->fds_bits[start], 0, left); 394 } 395 396 rcu_assign_pointer(newf->fdt, new_fdt); 397 398 return newf; 399 400 out_release: 401 kmem_cache_free(files_cachep, newf); 402 out: 403 return NULL; 404 } 405 406 static void __devinit fdtable_defer_list_init(int cpu) 407 { 408 struct fdtable_defer *fddef = &per_cpu(fdtable_defer_list, cpu); 409 spin_lock_init(&fddef->lock); 410 INIT_WORK(&fddef->wq, free_fdtable_work); 411 fddef->next = NULL; 412 } 413 414 void __init files_defer_init(void) 415 { 416 int i; 417 for_each_possible_cpu(i) 418 fdtable_defer_list_init(i); 419 sysctl_nr_open_max = min((size_t)INT_MAX, ~(size_t)0/sizeof(void *)) & 420 -BITS_PER_LONG; 421 } 422 423 struct files_struct init_files = { 424 .count = ATOMIC_INIT(1), 425 .fdt = &init_files.fdtab, 426 .fdtab = { 427 .max_fds = NR_OPEN_DEFAULT, 428 .fd = &init_files.fd_array[0], 429 .close_on_exec = (fd_set *)&init_files.close_on_exec_init, 430 .open_fds = (fd_set *)&init_files.open_fds_init, 431 .rcu = RCU_HEAD_INIT, 432 }, 433 .file_lock = __SPIN_LOCK_UNLOCKED(init_task.file_lock), 434 }; 435