fs/file.c

   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
  30 /*
  31  * We use this list to defer free fdtables that have vmalloced
  32  * sets/arrays. By keeping a per-cpu list, we avoid having to embed
  33  * the work_struct in fdtable itself which avoids a 64 byte (i386) increase in
  34  * this per-task structure.
  35  */
  36 static DEFINE_PER_CPU(struct fdtable_defer, fdtable_defer_list);
  37
  38 static inline void * alloc_fdmem(unsigned int size)
  39 {
  40         if (size <= PAGE_SIZE)
  41                 return kmalloc(size, GFP_KERNEL);
  42         else
  43                 return vmalloc(size);
  44 }
  45
  46 static inline void free_fdarr(struct fdtable *fdt)
  47 {
  48         if (fdt->max_fds <= (PAGE_SIZE / sizeof(struct file *)))
  49                 kfree(fdt->fd);
  50         else
  51                 vfree(fdt->fd);
  52 }
  53
  54 static inline void free_fdset(struct fdtable *fdt)
  55 {
  56         if (fdt->max_fds <= (PAGE_SIZE * BITS_PER_BYTE / 2))
  57                 kfree(fdt->open_fds);
  58         else
  59                 vfree(fdt->open_fds);
  60 }
  61
  62 static void free_fdtable_work(struct work_struct *work)
  63 {
  64         struct fdtable_defer *f =
  65                 container_of(work, struct fdtable_defer, wq);
  66         struct fdtable *fdt;
  67
  68         spin_lock_bh(&f->lock);
  69         fdt = f->next;
  70         f->next = NULL;
  71         spin_unlock_bh(&f->lock);
  72         while(fdt) {
  73                 struct fdtable *next = fdt->next;
  74                 vfree(fdt->fd);
  75                 free_fdset(fdt);
  76                 kfree(fdt);
  77                 fdt = next;
  78         }
  79 }
  80
  81 void free_fdtable_rcu(struct rcu_head *rcu)
  82 {
  83         struct fdtable *fdt = container_of(rcu, struct fdtable, rcu);
  84         struct fdtable_defer *fddef;
  85
  86         BUG_ON(!fdt);
  87
  88         if (fdt->max_fds <= NR_OPEN_DEFAULT) {
  89                 /*
  90                  * This fdtable is embedded in the files structure and that
  91                  * structure itself is getting destroyed.
  92                  */
  93                 kmem_cache_free(files_cachep,
  94                                 container_of(fdt, struct files_struct, fdtab));
  95                 return;
  96         }
  97         if (fdt->max_fds <= (PAGE_SIZE / sizeof(struct file *))) {
  98                 kfree(fdt->fd);
  99                 kfree(fdt->open_fds);
 100                 kfree(fdt);
 101         } else {
 102                 fddef = &get_cpu_var(fdtable_defer_list);
 103                 spin_lock(&fddef->lock);
 104                 fdt->next = fddef->next;
 105                 fddef->next = fdt;
 106                 /* vmallocs are handled from the workqueue context */
 107                 schedule_work(&fddef->wq);
 108                 spin_unlock(&fddef->lock);
 109                 put_cpu_var(fdtable_defer_list);
 110         }
 111 }
 112
 113 /*
 114  * Expand the fdset in the files_struct.  Called with the files spinlock
 115  * held for write.
 116  */
 117 static void copy_fdtable(struct fdtable *nfdt, struct fdtable *ofdt)
 118 {
 119         unsigned int cpy, set;
 120
 121         BUG_ON(nfdt->max_fds < ofdt->max_fds);
 122         if (ofdt->max_fds == 0)
 123                 return;
 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         /* Do we need to expand? */
 254         if (nr < fdt->max_fds)
 255                 return 0;
 256         /* Can we expand? */
 257         if (nr >= sysctl_nr_open)
 258                 return -EMFILE;
 259
 260         /* All good, so we try */
 261         return expand_fdtable(files, nr);
 262 }
 263
 264 static void __devinit fdtable_defer_list_init(int cpu)
 265 {
 266         struct fdtable_defer *fddef = &per_cpu(fdtable_defer_list, cpu);
 267         spin_lock_init(&fddef->lock);
 268         INIT_WORK(&fddef->wq, free_fdtable_work);
 269         fddef->next = NULL;
 270 }
 271
 272 void __init files_defer_init(void)
 273 {
 274         int i;
 275         for_each_possible_cpu(i)
 276                 fdtable_defer_list_init(i);
 277 }