linux/fs/file_table.c
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   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/lglock.h>
  24#include <linux/percpu_counter.h>
  25#include <linux/percpu.h>
  26#include <linux/hardirq.h>
  27#include <linux/task_work.h>
  28#include <linux/ima.h>
  29
  30#include <linux/atomic.h>
  31
  32#include "internal.h"
  33
  34/* sysctl tunables... */
  35struct files_stat_struct files_stat = {
  36        .max_files = NR_FILE
  37};
  38
  39DEFINE_STATIC_LGLOCK(files_lglock);
  40
  41/* SLAB cache for file structures */
  42static struct kmem_cache *filp_cachep __read_mostly;
  43
  44static struct percpu_counter nr_files __cacheline_aligned_in_smp;
  45
  46static void file_free_rcu(struct rcu_head *head)
  47{
  48        struct file *f = container_of(head, struct file, f_u.fu_rcuhead);
  49
  50        put_cred(f->f_cred);
  51        kmem_cache_free(filp_cachep, f);
  52}
  53
  54static inline void file_free(struct file *f)
  55{
  56        percpu_counter_dec(&nr_files);
  57        file_check_state(f);
  58        call_rcu(&f->f_u.fu_rcuhead, file_free_rcu);
  59}
  60
  61/*
  62 * Return the total number of open files in the system
  63 */
  64static long get_nr_files(void)
  65{
  66        return percpu_counter_read_positive(&nr_files);
  67}
  68
  69/*
  70 * Return the maximum number of open files in the system
  71 */
  72unsigned long get_max_files(void)
  73{
  74        return files_stat.max_files;
  75}
  76EXPORT_SYMBOL_GPL(get_max_files);
  77
  78/*
  79 * Handle nr_files sysctl
  80 */
  81#if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
  82int proc_nr_files(ctl_table *table, int write,
  83                     void __user *buffer, size_t *lenp, loff_t *ppos)
  84{
  85        files_stat.nr_files = get_nr_files();
  86        return proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
  87}
  88#else
  89int proc_nr_files(ctl_table *table, int write,
  90                     void __user *buffer, size_t *lenp, loff_t *ppos)
  91{
  92        return -ENOSYS;
  93}
  94#endif
  95
  96/* Find an unused file structure and return a pointer to it.
  97 * Returns an error pointer if some error happend e.g. we over file
  98 * structures limit, run out of memory or operation is not permitted.
  99 *
 100 * Be very careful using this.  You are responsible for
 101 * getting write access to any mount that you might assign
 102 * to this filp, if it is opened for write.  If this is not
 103 * done, you will imbalance int the mount's writer count
 104 * and a warning at __fput() time.
 105 */
 106struct file *get_empty_filp(void)
 107{
 108        const struct cred *cred = current_cred();
 109        static long old_max;
 110        struct file *f;
 111        int error;
 112
 113        /*
 114         * Privileged users can go above max_files
 115         */
 116        if (get_nr_files() >= files_stat.max_files && !capable(CAP_SYS_ADMIN)) {
 117                /*
 118                 * percpu_counters are inaccurate.  Do an expensive check before
 119                 * we go and fail.
 120                 */
 121                if (percpu_counter_sum_positive(&nr_files) >= files_stat.max_files)
 122                        goto over;
 123        }
 124
 125        f = kmem_cache_zalloc(filp_cachep, GFP_KERNEL);
 126        if (unlikely(!f))
 127                return ERR_PTR(-ENOMEM);
 128
 129        percpu_counter_inc(&nr_files);
 130        f->f_cred = get_cred(cred);
 131        error = security_file_alloc(f);
 132        if (unlikely(error)) {
 133                file_free(f);
 134                return ERR_PTR(error);
 135        }
 136
 137        INIT_LIST_HEAD(&f->f_u.fu_list);
 138        atomic_long_set(&f->f_count, 1);
 139        rwlock_init(&f->f_owner.lock);
 140        spin_lock_init(&f->f_lock);
 141        eventpoll_init_file(f);
 142        /* f->f_version: 0 */
 143        return f;
 144
 145over:
 146        /* Ran out of filps - report that */
 147        if (get_nr_files() > old_max) {
 148                pr_info("VFS: file-max limit %lu reached\n", get_max_files());
 149                old_max = get_nr_files();
 150        }
 151        return ERR_PTR(-ENFILE);
 152}
 153
 154/**
 155 * alloc_file - allocate and initialize a 'struct file'
 156 * @mnt: the vfsmount on which the file will reside
 157 * @dentry: the dentry representing the new file
 158 * @mode: the mode with which the new file will be opened
 159 * @fop: the 'struct file_operations' for the new file
 160 *
 161 * Use this instead of get_empty_filp() to get a new
 162 * 'struct file'.  Do so because of the same initialization
 163 * pitfalls reasons listed for init_file().  This is a
 164 * preferred interface to using init_file().
 165 *
 166 * If all the callers of init_file() are eliminated, its
 167 * code should be moved into this function.
 168 */
 169struct file *alloc_file(struct path *path, fmode_t mode,
 170                const struct file_operations *fop)
 171{
 172        struct file *file;
 173
 174        file = get_empty_filp();
 175        if (IS_ERR(file))
 176                return file;
 177
 178        file->f_path = *path;
 179        file->f_inode = path->dentry->d_inode;
 180        file->f_mapping = path->dentry->d_inode->i_mapping;
 181        file->f_mode = mode;
 182        file->f_op = fop;
 183
 184        /*
 185         * These mounts don't really matter in practice
 186         * for r/o bind mounts.  They aren't userspace-
 187         * visible.  We do this for consistency, and so
 188         * that we can do debugging checks at __fput()
 189         */
 190        if ((mode & FMODE_WRITE) && !special_file(path->dentry->d_inode->i_mode)) {
 191                file_take_write(file);
 192                WARN_ON(mnt_clone_write(path->mnt));
 193        }
 194        if ((mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
 195                i_readcount_inc(path->dentry->d_inode);
 196        return file;
 197}
 198EXPORT_SYMBOL(alloc_file);
 199
 200/**
 201 * drop_file_write_access - give up ability to write to a file
 202 * @file: the file to which we will stop writing
 203 *
 204 * This is a central place which will give up the ability
 205 * to write to @file, along with access to write through
 206 * its vfsmount.
 207 */
 208static void drop_file_write_access(struct file *file)
 209{
 210        struct vfsmount *mnt = file->f_path.mnt;
 211        struct dentry *dentry = file->f_path.dentry;
 212        struct inode *inode = dentry->d_inode;
 213
 214        put_write_access(inode);
 215
 216        if (special_file(inode->i_mode))
 217                return;
 218        if (file_check_writeable(file) != 0)
 219                return;
 220        __mnt_drop_write(mnt);
 221        file_release_write(file);
 222}
 223
 224/* the real guts of fput() - releasing the last reference to file
 225 */
 226static void __fput(struct file *file)
 227{
 228        struct dentry *dentry = file->f_path.dentry;
 229        struct vfsmount *mnt = file->f_path.mnt;
 230        struct inode *inode = file->f_inode;
 231
 232        might_sleep();
 233
 234        fsnotify_close(file);
 235        /*
 236         * The function eventpoll_release() should be the first called
 237         * in the file cleanup chain.
 238         */
 239        eventpoll_release(file);
 240        locks_remove_flock(file);
 241
 242        if (unlikely(file->f_flags & FASYNC)) {
 243                if (file->f_op && file->f_op->fasync)
 244                        file->f_op->fasync(-1, file, 0);
 245        }
 246        ima_file_free(file);
 247        if (file->f_op && file->f_op->release)
 248                file->f_op->release(inode, file);
 249        security_file_free(file);
 250        if (unlikely(S_ISCHR(inode->i_mode) && inode->i_cdev != NULL &&
 251                     !(file->f_mode & FMODE_PATH))) {
 252                cdev_put(inode->i_cdev);
 253        }
 254        fops_put(file->f_op);
 255        put_pid(file->f_owner.pid);
 256        if ((file->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
 257                i_readcount_dec(inode);
 258        if (file->f_mode & FMODE_WRITE)
 259                drop_file_write_access(file);
 260        file->f_path.dentry = NULL;
 261        file->f_path.mnt = NULL;
 262        file->f_inode = NULL;
 263        file_free(file);
 264        dput(dentry);
 265        mntput(mnt);
 266}
 267
 268static LLIST_HEAD(delayed_fput_list);
 269static void delayed_fput(struct work_struct *unused)
 270{
 271        struct llist_node *node = llist_del_all(&delayed_fput_list);
 272        struct llist_node *next;
 273
 274        for (; node; node = next) {
 275                next = llist_next(node);
 276                __fput(llist_entry(node, struct file, f_u.fu_llist));
 277        }
 278}
 279
 280static void ____fput(struct callback_head *work)
 281{
 282        __fput(container_of(work, struct file, f_u.fu_rcuhead));
 283}
 284
 285/*
 286 * If kernel thread really needs to have the final fput() it has done
 287 * to complete, call this.  The only user right now is the boot - we
 288 * *do* need to make sure our writes to binaries on initramfs has
 289 * not left us with opened struct file waiting for __fput() - execve()
 290 * won't work without that.  Please, don't add more callers without
 291 * very good reasons; in particular, never call that with locks
 292 * held and never call that from a thread that might need to do
 293 * some work on any kind of umount.
 294 */
 295void flush_delayed_fput(void)
 296{
 297        delayed_fput(NULL);
 298}
 299
 300static DECLARE_WORK(delayed_fput_work, delayed_fput);
 301
 302void fput(struct file *file)
 303{
 304        if (atomic_long_dec_and_test(&file->f_count)) {
 305                struct task_struct *task = current;
 306
 307                file_sb_list_del(file);
 308                if (likely(!in_interrupt() && !(task->flags & PF_KTHREAD))) {
 309                        init_task_work(&file->f_u.fu_rcuhead, ____fput);
 310                        if (!task_work_add(task, &file->f_u.fu_rcuhead, true))
 311                                return;
 312                        /*
 313                         * After this task has run exit_task_work(),
 314                         * task_work_add() will fail.  free_ipc_ns()->
 315                         * shm_destroy() can do this.  Fall through to delayed
 316                         * fput to avoid leaking *file.
 317                         */
 318                }
 319
 320                if (llist_add(&file->f_u.fu_llist, &delayed_fput_list))
 321                        schedule_work(&delayed_fput_work);
 322        }
 323}
 324
 325/*
 326 * synchronous analog of fput(); for kernel threads that might be needed
 327 * in some umount() (and thus can't use flush_delayed_fput() without
 328 * risking deadlocks), need to wait for completion of __fput() and know
 329 * for this specific struct file it won't involve anything that would
 330 * need them.  Use only if you really need it - at the very least,
 331 * don't blindly convert fput() by kernel thread to that.
 332 */
 333void __fput_sync(struct file *file)
 334{
 335        if (atomic_long_dec_and_test(&file->f_count)) {
 336                struct task_struct *task = current;
 337                file_sb_list_del(file);
 338                BUG_ON(!(task->flags & PF_KTHREAD));
 339                __fput(file);
 340        }
 341}
 342
 343EXPORT_SYMBOL(fput);
 344
 345void put_filp(struct file *file)
 346{
 347        if (atomic_long_dec_and_test(&file->f_count)) {
 348                security_file_free(file);
 349                file_sb_list_del(file);
 350                file_free(file);
 351        }
 352}
 353
 354static inline int file_list_cpu(struct file *file)
 355{
 356#ifdef CONFIG_SMP
 357        return file->f_sb_list_cpu;
 358#else
 359        return smp_processor_id();
 360#endif
 361}
 362
 363/* helper for file_sb_list_add to reduce ifdefs */
 364static inline void __file_sb_list_add(struct file *file, struct super_block *sb)
 365{
 366        struct list_head *list;
 367#ifdef CONFIG_SMP
 368        int cpu;
 369        cpu = smp_processor_id();
 370        file->f_sb_list_cpu = cpu;
 371        list = per_cpu_ptr(sb->s_files, cpu);
 372#else
 373        list = &sb->s_files;
 374#endif
 375        list_add(&file->f_u.fu_list, list);
 376}
 377
 378/**
 379 * file_sb_list_add - add a file to the sb's file list
 380 * @file: file to add
 381 * @sb: sb to add it to
 382 *
 383 * Use this function to associate a file with the superblock of the inode it
 384 * refers to.
 385 */
 386void file_sb_list_add(struct file *file, struct super_block *sb)
 387{
 388        lg_local_lock(&files_lglock);
 389        __file_sb_list_add(file, sb);
 390        lg_local_unlock(&files_lglock);
 391}
 392
 393/**
 394 * file_sb_list_del - remove a file from the sb's file list
 395 * @file: file to remove
 396 * @sb: sb to remove it from
 397 *
 398 * Use this function to remove a file from its superblock.
 399 */
 400void file_sb_list_del(struct file *file)
 401{
 402        if (!list_empty(&file->f_u.fu_list)) {
 403                lg_local_lock_cpu(&files_lglock, file_list_cpu(file));
 404                list_del_init(&file->f_u.fu_list);
 405                lg_local_unlock_cpu(&files_lglock, file_list_cpu(file));
 406        }
 407}
 408
 409#ifdef CONFIG_SMP
 410
 411/*
 412 * These macros iterate all files on all CPUs for a given superblock.
 413 * files_lglock must be held globally.
 414 */
 415#define do_file_list_for_each_entry(__sb, __file)               \
 416{                                                               \
 417        int i;                                                  \
 418        for_each_possible_cpu(i) {                              \
 419                struct list_head *list;                         \
 420                list = per_cpu_ptr((__sb)->s_files, i);         \
 421                list_for_each_entry((__file), list, f_u.fu_list)
 422
 423#define while_file_list_for_each_entry                          \
 424        }                                                       \
 425}
 426
 427#else
 428
 429#define do_file_list_for_each_entry(__sb, __file)               \
 430{                                                               \
 431        struct list_head *list;                                 \
 432        list = &(sb)->s_files;                                  \
 433        list_for_each_entry((__file), list, f_u.fu_list)
 434
 435#define while_file_list_for_each_entry                          \
 436}
 437
 438#endif
 439
 440/**
 441 *      mark_files_ro - mark all files read-only
 442 *      @sb: superblock in question
 443 *
 444 *      All files are marked read-only.  We don't care about pending
 445 *      delete files so this should be used in 'force' mode only.
 446 */
 447void mark_files_ro(struct super_block *sb)
 448{
 449        struct file *f;
 450
 451        lg_global_lock(&files_lglock);
 452        do_file_list_for_each_entry(sb, f) {
 453                if (!S_ISREG(file_inode(f)->i_mode))
 454                       continue;
 455                if (!file_count(f))
 456                        continue;
 457                if (!(f->f_mode & FMODE_WRITE))
 458                        continue;
 459                spin_lock(&f->f_lock);
 460                f->f_mode &= ~FMODE_WRITE;
 461                spin_unlock(&f->f_lock);
 462                if (file_check_writeable(f) != 0)
 463                        continue;
 464                __mnt_drop_write(f->f_path.mnt);
 465                file_release_write(f);
 466        } while_file_list_for_each_entry;
 467        lg_global_unlock(&files_lglock);
 468}
 469
 470void __init files_init(unsigned long mempages)
 471{ 
 472        unsigned long n;
 473
 474        filp_cachep = kmem_cache_create("filp", sizeof(struct file), 0,
 475                        SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
 476
 477        /*
 478         * One file with associated inode and dcache is very roughly 1K.
 479         * Per default don't use more than 10% of our memory for files. 
 480         */ 
 481
 482        n = (mempages * (PAGE_SIZE / 1024)) / 10;
 483        files_stat.max_files = max_t(unsigned long, n, NR_FILE);
 484        files_defer_init();
 485        lg_lock_init(&files_lglock, "files_lglock");
 486        percpu_counter_init(&nr_files, 0);
 487} 
 488
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