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Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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SPDX-License-Identifier: GPL-2.0/* * linux/fs/super.c * * Copyright (C) 1991, 1992 Linus Torvalds * * super.c contains code to handle: - mount structures * - super-block tables * - filesystem drivers list * - mount system call * - umount system call * - ustat system call * * GK 2/5/95 - Changed to support mounting the root fs via NFS * * Added kerneld support: Jacques Gelinas and Bjorn Ekwall * Added change_root: Werner Almesberger & Hans Lermen, Feb '96 * Added options to /proc/mounts: * Torbjörn Lindh (torbjorn.lindh@gopta.se), April 14, 1996. * Added devfs support: Richard Gooch <rgooch@atnf.csiro.au>, 13-JAN-1998 * Heavily rewritten for 'one fs - one tree' dcache architecture. AV, Mar 2000 */
#include <linux/export.h>#include <linux/slab.h>#include <linux/blkdev.h>#include <linux/mount.h>#include <linux/security.h>#include <linux/writeback.h> /* for the emergency remount stuff */#include <linux/idr.h>#include <linux/mutex.h>#include <linux/backing-dev.h>#include <linux/rculist_bl.h>#include <linux/fscrypt.h>#include <linux/fsnotify.h>#include <linux/lockdep.h>#include <linux/user_namespace.h>#include <linux/fs_context.h>#include <linux/fserror.h>#include <uapi/linux/mount.h>#include "internal.h"
static int thaw_super_locked(struct super_block *sb, enum freeze_holder who, const void *freeze_owner);
static LIST_HEAD(super_blocks);static DEFINE_SPINLOCK(sb_lock);
static char *sb_writers_name[SB_FREEZE_LEVELS] = { "sb_writers", "sb_pagefaults", "sb_internal",};
static inline void __super_lock(struct super_block *sb, bool excl){ if (excl) down_write(&sb->s_umount); else down_read(&sb->s_umount);}
static inline void super_unlock(struct super_block *sb, bool excl){ if (excl) up_write(&sb->s_umount); else up_read(&sb->s_umount);}
static inline void __super_lock_excl(struct super_block *sb){ __super_lock(sb, true);}
static inline void super_unlock_excl(struct super_block *sb){ super_unlock(sb, true);}
static inline void super_unlock_shared(struct super_block *sb){ super_unlock(sb, false);}
static bool super_flags(const struct super_block *sb, unsigned int flags){ /* * Pairs with smp_store_release() in super_wake() and ensures * that we see @flags after we're woken. */ return smp_load_acquire(&sb->s_flags) & flags;}
/** * super_lock - wait for superblock to become ready and lock it * @sb: superblock to wait for * @excl: whether exclusive access is required * * If the superblock has neither passed through vfs_get_tree() or * generic_shutdown_super() yet wait for it to happen. Either superblock * creation will succeed and SB_BORN is set by vfs_get_tree() or we're * woken and we'll see SB_DYING. * * The caller must have acquired a temporary reference on @sb->s_count. * * Return: The function returns true if SB_BORN was set and with * s_umount held. The function returns false if SB_DYING was * set and without s_umount held. */static __must_check bool super_lock(struct super_block *sb, bool excl){ lockdep_assert_not_held(&sb->s_umount);
/* wait until the superblock is ready or dying */ wait_var_event(&sb->s_flags, super_flags(sb, SB_BORN | SB_DYING));
/* Don't pointlessly acquire s_umount. */ if (super_flags(sb, SB_DYING)) return false;
__super_lock(sb, excl);
/* * Has gone through generic_shutdown_super() in the meantime. * @sb->s_root is NULL and @sb->s_active is 0. No one needs to * grab a reference to this. Tell them so. */ if (sb->s_flags & SB_DYING) { super_unlock(sb, excl); return false; }
WARN_ON_ONCE(!(sb->s_flags & SB_BORN)); return true;}
/* wait and try to acquire read-side of @sb->s_umount */static inline bool super_lock_shared(struct super_block *sb){ return super_lock(sb, false);}
/* wait and try to acquire write-side of @sb->s_umount */static inline bool super_lock_excl(struct super_block *sb){ return super_lock(sb, true);}
/* wake waiters */#define SUPER_WAKE_FLAGS (SB_BORN | SB_DYING | SB_DEAD)static void super_wake(struct super_block *sb, unsigned int flag){ WARN_ON_ONCE((flag & ~SUPER_WAKE_FLAGS)); WARN_ON_ONCE(hweight32(flag & SUPER_WAKE_FLAGS) > 1);
/* * Pairs with smp_load_acquire() in super_lock() to make sure * all initializations in the superblock are seen by the user * seeing SB_BORN sent. */ smp_store_release(&sb->s_flags, sb->s_flags | flag); /* * Pairs with the barrier in prepare_to_wait_event() to make sure * ___wait_var_event() either sees SB_BORN set or * waitqueue_active() check in wake_up_var() sees the waiter. */ smp_mb(); wake_up_var(&sb->s_flags);}
/* * One thing we have to be careful of with a per-sb shrinker is that we don't * drop the last active reference to the superblock from within the shrinker. * If that happens we could trigger unregistering the shrinker from within the * shrinker path and that leads to deadlock on the shrinker_mutex. Hence we * take a passive reference to the superblock to avoid this from occurring. */static unsigned long super_cache_scan(struct shrinker *shrink, struct shrink_control *sc){ struct super_block *sb; long fs_objects = 0; long total_objects; long freed = 0; long dentries; long inodes;
sb = shrink->private_data;
/* * Deadlock avoidance. We may hold various FS locks, and we don't want * to recurse into the FS that called us in clear_inode() and friends.. */ if (!(sc->gfp_mask & __GFP_FS)) return SHRINK_STOP;
if (!super_trylock_shared(sb)) return SHRINK_STOP;
if (sb->s_op->nr_cached_objects) fs_objects = sb->s_op->nr_cached_objects(sb, sc);
inodes = list_lru_shrink_count(&sb->s_inode_lru, sc); dentries = list_lru_shrink_count(&sb->s_dentry_lru, sc); total_objects = dentries + inodes + fs_objects; if (!total_objects) total_objects = 1;
/* proportion the scan between the caches */ dentries = mult_frac(sc->nr_to_scan, dentries, total_objects); inodes = mult_frac(sc->nr_to_scan, inodes, total_objects); fs_objects = mult_frac(sc->nr_to_scan, fs_objects, total_objects);
/* * prune the dcache first as the icache is pinned by it, then * prune the icache, followed by the filesystem specific caches * * Ensure that we always scan at least one object - memcg kmem * accounting uses this to fully empty the caches. */ sc->nr_to_scan = dentries + 1; freed = prune_dcache_sb(sb, sc); sc->nr_to_scan = inodes + 1; freed += prune_icache_sb(sb, sc);
if (fs_objects) { sc->nr_to_scan = fs_objects + 1; freed += sb->s_op->free_cached_objects(sb, sc); }
super_unlock_shared(sb); return freed;}
static unsigned long super_cache_count(struct shrinker *shrink, struct shrink_control *sc){ struct super_block *sb; long total_objects = 0;
sb = shrink->private_data;
/* * We don't call super_trylock_shared() here as it is a scalability * bottleneck, so we're exposed to partial setup state. The shrinker * rwsem does not protect filesystem operations backing * list_lru_shrink_count() or s_op->nr_cached_objects(). Counts can * change between super_cache_count and super_cache_scan, so we really * don't need locks here. * * However, if we are currently mounting the superblock, the underlying * filesystem might be in a state of partial construction and hence it * is dangerous to access it. super_trylock_shared() uses a SB_BORN check * to avoid this situation, so do the same here. The memory barrier is * matched with the one in mount_fs() as we don't hold locks here. */ if (!(sb->s_flags & SB_BORN)) return 0; smp_rmb();
if (sb->s_op && sb->s_op->nr_cached_objects) total_objects = sb->s_op->nr_cached_objects(sb, sc);
total_objects += list_lru_shrink_count(&sb->s_dentry_lru, sc); total_objects += list_lru_shrink_count(&sb->s_inode_lru, sc);
if (!total_objects) return SHRINK_EMPTY;
total_objects = vfs_pressure_ratio(total_objects); return total_objects;}
static void destroy_super_work(struct work_struct *work){ struct super_block *s = container_of(work, struct super_block, destroy_work); fsnotify_sb_free(s); security_sb_free(s); put_user_ns(s->s_user_ns); kfree(s->s_subtype); for (int i = 0; i < SB_FREEZE_LEVELS; i++) percpu_free_rwsem(&s->s_writers.rw_sem[i]); kfree(s);}
static void destroy_super_rcu(struct rcu_head *head){ struct super_block *s = container_of(head, struct super_block, rcu); INIT_WORK(&s->destroy_work, destroy_super_work); schedule_work(&s->destroy_work);}
/* Free a superblock that has never been seen by anyone */static void destroy_unused_super(struct super_block *s){ if (!s) return; super_unlock_excl(s); list_lru_destroy(&s->s_dentry_lru); list_lru_destroy(&s->s_inode_lru); shrinker_free(s->s_shrink); /* no delays needed */ destroy_super_work(&s->destroy_work);}
/** * alloc_super - create new superblock * @type: filesystem type superblock should belong to * @flags: the mount flags * @user_ns: User namespace for the super_block * * Allocates and initializes a new &struct super_block. alloc_super() * returns a pointer new superblock or %NULL if allocation had failed. */static struct super_block *alloc_super(struct file_system_type *type, int flags, struct user_namespace *user_ns){ struct super_block *s = kzalloc_obj(struct super_block); static const struct super_operations default_op; int i;
if (!s) return NULL;
s->s_user_ns = get_user_ns(user_ns); init_rwsem(&s->s_umount); lockdep_set_class(&s->s_umount, &type->s_umount_key); /* * sget_fc() can have s_umount recursion. * * When it cannot find a suitable sb, it allocates a new * one (this one), and tries again to find a suitable old * one. * * In case that succeeds, it will acquire the s_umount * lock of the old one. Since these are clearly distrinct * locks, and this object isn't exposed yet, there's no * risk of deadlocks. * * Annotate this by putting this lock in a different * subclass. */ down_write_nested(&s->s_umount, SINGLE_DEPTH_NESTING);
if (security_sb_alloc(s)) goto fail;
for (i = 0; i < SB_FREEZE_LEVELS; i++) { if (__percpu_init_rwsem(&s->s_writers.rw_sem[i], sb_writers_name[i], &type->s_writers_key[i])) goto fail; } s->s_bdi = &noop_backing_dev_info; s->s_flags = flags; if (s->s_user_ns != &init_user_ns) s->s_iflags |= SB_I_NODEV; INIT_HLIST_NODE(&s->s_instances); INIT_HLIST_BL_HEAD(&s->s_roots); spin_lock_init(&s->s_roots_lock); mutex_init(&s->s_sync_lock); INIT_LIST_HEAD(&s->s_inodes); spin_lock_init(&s->s_inode_list_lock); INIT_LIST_HEAD(&s->s_inodes_wb); spin_lock_init(&s->s_inode_wblist_lock); fserror_mount(s);
s->s_count = 1; atomic_set(&s->s_active, 1); mutex_init(&s->s_vfs_rename_mutex); lockdep_set_class(&s->s_vfs_rename_mutex, &type->s_vfs_rename_key); init_rwsem(&s->s_dquot.dqio_sem); s->s_maxbytes = MAX_NON_LFS; s->s_op = &default_op; s->s_time_gran = 1000000000; s->s_time_min = TIME64_MIN; s->s_time_max = TIME64_MAX;
s->s_shrink = shrinker_alloc(SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE, "sb-%s", type->name); if (!s->s_shrink) goto fail;
s->s_shrink->scan_objects = super_cache_scan; s->s_shrink->count_objects = super_cache_count; s->s_shrink->batch = 1024; s->s_shrink->private_data = s;
if (list_lru_init_memcg(&s->s_dentry_lru, s->s_shrink)) goto fail; if (list_lru_init_memcg(&s->s_inode_lru, s->s_shrink)) goto fail; s->s_min_writeback_pages = MIN_WRITEBACK_PAGES; return s;
fail: destroy_unused_super(s); return NULL;}
/* Superblock refcounting */
/* * Drop a superblock's refcount. The caller must hold sb_lock. */static void __put_super(struct super_block *s){ if (!--s->s_count) { list_del_init(&s->s_list); WARN_ON(s->s_dentry_lru.node); WARN_ON(s->s_inode_lru.node); WARN_ON(s->s_mounts); call_rcu(&s->rcu, destroy_super_rcu); }}
/** * put_super - drop a temporary reference to superblock * @sb: superblock in question * * Drops a temporary reference, frees superblock if there's no * references left. */void put_super(struct super_block *sb){ spin_lock(&sb_lock); __put_super(sb); spin_unlock(&sb_lock);}
static void kill_super_notify(struct super_block *sb){ lockdep_assert_not_held(&sb->s_umount);
/* already notified earlier */ if (sb->s_flags & SB_DEAD) return;
/* * Remove it from @fs_supers so it isn't found by new * sget_fc() walkers anymore. Any concurrent mounter still * managing to grab a temporary reference is guaranteed to * already see SB_DYING and will wait until we notify them about * SB_DEAD. */ spin_lock(&sb_lock); hlist_del_init(&sb->s_instances); spin_unlock(&sb_lock);
/* * Let concurrent mounts know that this thing is really dead. * We don't need @sb->s_umount here as every concurrent caller * will see SB_DYING and either discard the superblock or wait * for SB_DEAD. */ super_wake(sb, SB_DEAD);}
/** * deactivate_locked_super - drop an active reference to superblock * @s: superblock to deactivate * * Drops an active reference to superblock, converting it into a temporary * one if there is no other active references left. In that case we * tell fs driver to shut it down and drop the temporary reference we * had just acquired. * * Caller holds exclusive lock on superblock; that lock is released. */void deactivate_locked_super(struct super_block *s){ struct file_system_type *fs = s->s_type; if (atomic_dec_and_test(&s->s_active)) { shrinker_free(s->s_shrink); fs->kill_sb(s);
kill_super_notify(s);
/* * Since list_lru_destroy() may sleep, we cannot call it from * put_super(), where we hold the sb_lock. Therefore we destroy * the lru lists right now. */ list_lru_destroy(&s->s_dentry_lru); list_lru_destroy(&s->s_inode_lru);
put_filesystem(fs); put_super(s); } else { super_unlock_excl(s); }}
EXPORT_SYMBOL(deactivate_locked_super);
/** * deactivate_super - drop an active reference to superblock * @s: superblock to deactivate * * Variant of deactivate_locked_super(), except that superblock is *not* * locked by caller. If we are going to drop the final active reference, * lock will be acquired prior to that. */void deactivate_super(struct super_block *s){ if (!atomic_add_unless(&s->s_active, -1, 1)) { __super_lock_excl(s); deactivate_locked_super(s); }}
EXPORT_SYMBOL(deactivate_super);
/** * grab_super - acquire an active reference to a superblock * @sb: superblock to acquire * * Acquire a temporary reference on a superblock and try to trade it for * an active reference. This is used in sget_fc() to wait for a * superblock to either become SB_BORN or for it to pass through * sb->kill() and be marked as SB_DEAD. * * Return: This returns true if an active reference could be acquired, * false if not. */static bool grab_super(struct super_block *sb){ bool locked;
sb->s_count++; spin_unlock(&sb_lock); locked = super_lock_excl(sb); if (locked) { if (atomic_inc_not_zero(&sb->s_active)) { put_super(sb); return true; } super_unlock_excl(sb); } wait_var_event(&sb->s_flags, super_flags(sb, SB_DEAD)); put_super(sb); return false;}
/* * super_trylock_shared - try to grab ->s_umount shared * @sb: reference we are trying to grab * * Try to prevent fs shutdown. This is used in places where we * cannot take an active reference but we need to ensure that the * filesystem is not shut down while we are working on it. It returns * false if we cannot acquire s_umount or if we lose the race and * filesystem already got into shutdown, and returns true with the s_umount * lock held in read mode in case of success. On successful return, * the caller must drop the s_umount lock when done. * * Note that unlike get_super() et.al. this one does *not* bump ->s_count. * The reason why it's safe is that we are OK with doing trylock instead * of down_read(). There's a couple of places that are OK with that, but * it's very much not a general-purpose interface. */bool super_trylock_shared(struct super_block *sb){ if (down_read_trylock(&sb->s_umount)) { if (!(sb->s_flags & SB_DYING) && sb->s_root && (sb->s_flags & SB_BORN)) return true; super_unlock_shared(sb); }
return false;}
/** * retire_super - prevents superblock from being reused * @sb: superblock to retire * * The function marks superblock to be ignored in superblock test, which * prevents it from being reused for any new mounts. If the superblock has * a private bdi, it also unregisters it, but doesn't reduce the refcount * of the superblock to prevent potential races. The refcount is reduced * by generic_shutdown_super(). The function can not be called * concurrently with generic_shutdown_super(). It is safe to call the * function multiple times, subsequent calls have no effect. * * The marker will affect the re-use only for block-device-based * superblocks. Other superblocks will still get marked if this function * is used, but that will not affect their reusability. */void retire_super(struct super_block *sb){ WARN_ON(!sb->s_bdev); __super_lock_excl(sb); if (sb->s_iflags & SB_I_PERSB_BDI) { bdi_unregister(sb->s_bdi); sb->s_iflags &= ~SB_I_PERSB_BDI; } sb->s_iflags |= SB_I_RETIRED; super_unlock_excl(sb);}EXPORT_SYMBOL(retire_super);
/** * generic_shutdown_super - common helper for ->kill_sb() * @sb: superblock to kill * * generic_shutdown_super() does all fs-independent work on superblock * shutdown. Typical ->kill_sb() should pick all fs-specific objects * that need destruction out of superblock, call generic_shutdown_super() * and release aforementioned objects. Note: dentries and inodes _are_ * taken care of and do not need specific handling. * * Upon calling this function, the filesystem may no longer alter or * rearrange the set of dentries belonging to this super_block, nor may it * change the attachments of dentries to inodes. */void generic_shutdown_super(struct super_block *sb){ const struct super_operations *sop = sb->s_op;
if (sb->s_root) { fsnotify_sb_delete(sb); shrink_dcache_for_umount(sb); sync_filesystem(sb); sb->s_flags &= ~SB_ACTIVE;
fserror_unmount(sb); cgroup_writeback_umount(sb);
/* Evict all inodes with zero refcount. */ evict_inodes(sb);
/* * Clean up and evict any inodes that still have references due * to the security policy. */ security_sb_delete(sb);
if (sb->s_dio_done_wq) { destroy_workqueue(sb->s_dio_done_wq); sb->s_dio_done_wq = NULL; }
if (sop->put_super) sop->put_super(sb);
/* * Now that all potentially-encrypted inodes have been evicted, * the fscrypt keyring can be destroyed. */ fscrypt_destroy_keyring(sb);
if (CHECK_DATA_CORRUPTION(!list_empty(&sb->s_inodes), NULL, "VFS: Busy inodes after unmount of %s (%s)", sb->s_id, sb->s_type->name)) { /* * Adding a proper bailout path here would be hard, but * we can at least make it more likely that a later * iput_final() or such crashes cleanly. */ struct inode *inode;
spin_lock(&sb->s_inode_list_lock); list_for_each_entry(inode, &sb->s_inodes, i_sb_list) { inode->i_op = VFS_PTR_POISON; inode->i_sb = VFS_PTR_POISON; inode->i_mapping = VFS_PTR_POISON; } spin_unlock(&sb->s_inode_list_lock); } } /* * Broadcast to everyone that grabbed a temporary reference to this * superblock before we removed it from @fs_supers that the superblock * is dying. Every walker of @fs_supers outside of sget_fc() will now * discard this superblock and treat it as dead. * * We leave the superblock on @fs_supers so it can be found by * sget_fc() until we passed sb->kill_sb(). */ super_wake(sb, SB_DYING); super_unlock_excl(sb); if (sb->s_bdi != &noop_backing_dev_info) { if (sb->s_iflags & SB_I_PERSB_BDI) bdi_unregister(sb->s_bdi); bdi_put(sb->s_bdi); sb->s_bdi = &noop_backing_dev_info; }}
EXPORT_SYMBOL(generic_shutdown_super);
bool mount_capable(struct fs_context *fc){ if (!(fc->fs_type->fs_flags & FS_USERNS_MOUNT)) return capable(CAP_SYS_ADMIN); else return ns_capable(fc->user_ns, CAP_SYS_ADMIN);}
/** * sget_fc - Find or create a superblock * @fc: Filesystem context. * @test: Comparison callback * @set: Setup callback * * Create a new superblock or find an existing one. * * The @test callback is used to find a matching existing superblock. * Whether or not the requested parameters in @fc are taken into account * is specific to the @test callback that is used. They may even be * completely ignored. * * If an extant superblock is matched, it will be returned unless: * * (1) the namespace the filesystem context @fc and the extant * superblock's namespace differ * * (2) the filesystem context @fc has requested that reusing an extant * superblock is not allowed * * In both cases EBUSY will be returned. * * If no match is made, a new superblock will be allocated and basic * initialisation will be performed (s_type, s_fs_info and s_id will be * set and the @set callback will be invoked), the superblock will be * published and it will be returned in a partially constructed state * with SB_BORN and SB_ACTIVE as yet unset. * * Return: On success, an extant or newly created superblock is * returned. On failure an error pointer is returned. */struct super_block *sget_fc(struct fs_context *fc, int (*test)(struct super_block *, struct fs_context *), int (*set)(struct super_block *, struct fs_context *)){ struct super_block *s = NULL; struct super_block *old; struct user_namespace *user_ns = fc->global ? &init_user_ns : fc->user_ns; int err;
/* * Never allow s_user_ns != &init_user_ns when FS_USERNS_MOUNT or * FS_USERNS_DELEGATABLE is not set, as the filesystem is likely * unprepared to handle it. This can happen when fsconfig() is called * from init_user_ns with an fs_fd opened in another user namespace. */ if (user_ns != &init_user_ns && !(fc->fs_type->fs_flags & (FS_USERNS_MOUNT | FS_USERNS_DELEGATABLE))) { errorfc(fc, "VFS: Mounting from non-initial user namespace is not allowed"); return ERR_PTR(-EPERM); }
retry: spin_lock(&sb_lock); if (test) { hlist_for_each_entry(old, &fc->fs_type->fs_supers, s_instances) { if (test(old, fc)) goto share_extant_sb; } } if (!s) { spin_unlock(&sb_lock); s = alloc_super(fc->fs_type, fc->sb_flags, user_ns); if (!s) return ERR_PTR(-ENOMEM); goto retry; }
s->s_fs_info = fc->s_fs_info; err = set(s, fc); if (err) { s->s_fs_info = NULL; spin_unlock(&sb_lock); destroy_unused_super(s); return ERR_PTR(err); } fc->s_fs_info = NULL; s->s_type = fc->fs_type; s->s_iflags |= fc->s_iflags; strscpy(s->s_id, s->s_type->name, sizeof(s->s_id)); /* * Make the superblock visible on @super_blocks and @fs_supers. * It's in a nascent state and users should wait on SB_BORN or * SB_DYING to be set. */ list_add_tail(&s->s_list, &super_blocks); hlist_add_head(&s->s_instances, &s->s_type->fs_supers); spin_unlock(&sb_lock); get_filesystem(s->s_type); shrinker_register(s->s_shrink); return s;
share_extant_sb: if (user_ns != old->s_user_ns || fc->exclusive) { spin_unlock(&sb_lock); destroy_unused_super(s); if (fc->exclusive) warnfc(fc, "reusing existing filesystem not allowed"); else warnfc(fc, "reusing existing filesystem in another namespace not allowed"); return ERR_PTR(-EBUSY); } if (!grab_super(old)) goto retry; destroy_unused_super(s); return old;}EXPORT_SYMBOL(sget_fc);
void drop_super(struct super_block *sb){ super_unlock_shared(sb); put_super(sb);}
EXPORT_SYMBOL(drop_super);
void drop_super_exclusive(struct super_block *sb){ super_unlock_excl(sb); put_super(sb);}
enum super_iter_flags_t { SUPER_ITER_EXCL = (1U << 0), SUPER_ITER_UNLOCKED = (1U << 1), SUPER_ITER_REVERSE = (1U << 2),};
static inline struct super_block *first_super(enum super_iter_flags_t flags){ if (flags & SUPER_ITER_REVERSE) return list_last_entry(&super_blocks, struct super_block, s_list); return list_first_entry(&super_blocks, struct super_block, s_list);}
static inline struct super_block *next_super(struct super_block *sb, enum super_iter_flags_t flags){ if (flags & SUPER_ITER_REVERSE) return list_prev_entry(sb, s_list); return list_next_entry(sb, s_list);}
static void __iterate_supers(void (*f)(struct super_block *, void *), void *arg, enum super_iter_flags_t flags){ struct super_block *sb, *p = NULL; bool excl = flags & SUPER_ITER_EXCL;
guard(spinlock)(&sb_lock);
for (sb = first_super(flags); !list_entry_is_head(sb, &super_blocks, s_list); sb = next_super(sb, flags)) { if (super_flags(sb, SB_DYING)) continue; sb->s_count++; spin_unlock(&sb_lock);
if (flags & SUPER_ITER_UNLOCKED) { f(sb, arg); } else if (super_lock(sb, excl)) { f(sb, arg); super_unlock(sb, excl); }
spin_lock(&sb_lock); if (p) __put_super(p); p = sb; } if (p) __put_super(p);}
void iterate_supers(void (*f)(struct super_block *, void *), void *arg){ __iterate_supers(f, arg, 0);}
/** * iterate_supers_type - call function for superblocks of given type * @type: fs type * @f: function to call * @arg: argument to pass to it * * Scans the superblock list and calls given function, passing it * locked superblock and given argument. */void iterate_supers_type(struct file_system_type *type, void (*f)(struct super_block *, void *), void *arg){ struct super_block *sb, *p = NULL;
spin_lock(&sb_lock); hlist_for_each_entry(sb, &type->fs_supers, s_instances) { bool locked;
if (super_flags(sb, SB_DYING)) continue;
sb->s_count++; spin_unlock(&sb_lock);
locked = super_lock_shared(sb); if (locked) { f(sb, arg); super_unlock_shared(sb); }
spin_lock(&sb_lock); if (p) __put_super(p); p = sb; } if (p) __put_super(p); spin_unlock(&sb_lock);}
EXPORT_SYMBOL(iterate_supers_type);
struct super_block *user_get_super(dev_t dev, bool excl){ struct super_block *sb;
spin_lock(&sb_lock); list_for_each_entry(sb, &super_blocks, s_list) { bool locked;
if (sb->s_dev != dev) continue;
sb->s_count++; spin_unlock(&sb_lock);
locked = super_lock(sb, excl); if (locked) return sb;
spin_lock(&sb_lock); __put_super(sb); break; } spin_unlock(&sb_lock); return NULL;}
/** * reconfigure_super - asks filesystem to change superblock parameters * @fc: The superblock and configuration * * Alters the configuration parameters of a live superblock. */int reconfigure_super(struct fs_context *fc){ struct super_block *sb = fc->root->d_sb; int retval; bool remount_ro = false; bool remount_rw = false; bool force = fc->sb_flags & SB_FORCE;
if (fc->sb_flags_mask & ~MS_RMT_MASK) return -EINVAL; if (sb->s_writers.frozen != SB_UNFROZEN) return -EBUSY;
retval = security_sb_remount(sb, fc->security); if (retval) return retval;
if (fc->sb_flags_mask & SB_RDONLY) {#ifdef CONFIG_BLOCK if (!(fc->sb_flags & SB_RDONLY) && sb->s_bdev && bdev_read_only(sb->s_bdev)) return -EACCES;#endif remount_rw = !(fc->sb_flags & SB_RDONLY) && sb_rdonly(sb); remount_ro = (fc->sb_flags & SB_RDONLY) && !sb_rdonly(sb); }
if (remount_ro) { if (!hlist_empty(&sb->s_pins)) { super_unlock_excl(sb); group_pin_kill(&sb->s_pins); __super_lock_excl(sb); if (!sb->s_root) return 0; if (sb->s_writers.frozen != SB_UNFROZEN) return -EBUSY; remount_ro = !sb_rdonly(sb); } } shrink_dcache_sb(sb);
/* If we are reconfiguring to RDONLY and current sb is read/write, * make sure there are no files open for writing. */ if (remount_ro) { if (force) { sb_start_ro_state_change(sb); } else { retval = sb_prepare_remount_readonly(sb); if (retval) return retval; } } else if (remount_rw) { /* * Protect filesystem's reconfigure code from writes from * userspace until reconfigure finishes. */ sb_start_ro_state_change(sb); }
if (fc->ops->reconfigure) { retval = fc->ops->reconfigure(fc); if (retval) { if (!force) goto cancel_readonly; /* If forced remount, go ahead despite any errors */ WARN(1, "forced remount of a %s fs returned %i\n", sb->s_type->name, retval); } }
WRITE_ONCE(sb->s_flags, ((sb->s_flags & ~fc->sb_flags_mask) | (fc->sb_flags & fc->sb_flags_mask))); sb_end_ro_state_change(sb);
/* * Some filesystems modify their metadata via some other path than the * bdev buffer cache (eg. use a private mapping, or directories in * pagecache, etc). Also file data modifications go via their own * mappings. So If we try to mount readonly then copy the filesystem * from bdev, we could get stale data, so invalidate it to give a best * effort at coherency. */ if (remount_ro && sb->s_bdev) invalidate_bdev(sb->s_bdev); return 0;
cancel_readonly: sb_end_ro_state_change(sb); return retval;}
static void do_emergency_remount_callback(struct super_block *sb, void *unused){ if (sb->s_bdev && !sb_rdonly(sb)) { struct fs_context *fc;
fc = fs_context_for_reconfigure(sb->s_root, SB_RDONLY | SB_FORCE, SB_RDONLY); if (!IS_ERR(fc)) { if (parse_monolithic_mount_data(fc, NULL) == 0) (void)reconfigure_super(fc); put_fs_context(fc); } }}
static void do_emergency_remount(struct work_struct *work){ __iterate_supers(do_emergency_remount_callback, NULL, SUPER_ITER_EXCL | SUPER_ITER_REVERSE); kfree(work); printk("Emergency Remount complete\n");}
void emergency_remount(void){ struct work_struct *work;
work = kmalloc_obj(*work, GFP_ATOMIC); if (work) { INIT_WORK(work, do_emergency_remount); schedule_work(work); }}
static inline bool get_active_super(struct super_block *sb){ bool active = false;
if (super_lock_excl(sb)) { active = atomic_inc_not_zero(&sb->s_active); super_unlock_excl(sb); } return active;}
static void do_thaw_all_callback(struct super_block *sb, void *unused){ if (!get_active_super(sb)) return;
/* fs_bdev_thaw() acquires s_umount so it must not be held here */ if (IS_ENABLED(CONFIG_BLOCK)) while (sb->s_bdev && !bdev_thaw(sb->s_bdev)) pr_warn("Emergency Thaw on %pg\n", sb->s_bdev);
if (super_lock_excl(sb)) thaw_super_locked(sb, FREEZE_HOLDER_USERSPACE, NULL); deactivate_super(sb);}
static void do_thaw_all(struct work_struct *work){ __iterate_supers(do_thaw_all_callback, NULL, SUPER_ITER_UNLOCKED); kfree(work); printk(KERN_WARNING "Emergency Thaw complete\n");}
/** * emergency_thaw_all -- forcibly thaw every frozen filesystem * * Used for emergency unfreeze of all filesystems via SysRq */void emergency_thaw_all(void){ struct work_struct *work;
work = kmalloc_obj(*work, GFP_ATOMIC); if (work) { INIT_WORK(work, do_thaw_all); schedule_work(work); }}
static const char *filesystems_freeze_ptr = "filesystems_freeze";
static void filesystems_freeze_callback(struct super_block *sb, void *freeze_all_ptr){ if (!sb->s_op->freeze_fs && !sb->s_op->freeze_super) return;
if (!freeze_all_ptr && !(sb->s_type->fs_flags & FS_POWER_FREEZE)) return;
if (!get_active_super(sb)) return;
if (sb->s_op->freeze_super) sb->s_op->freeze_super(sb, FREEZE_EXCL | FREEZE_HOLDER_KERNEL, filesystems_freeze_ptr); else freeze_super(sb, FREEZE_EXCL | FREEZE_HOLDER_KERNEL, filesystems_freeze_ptr);
deactivate_super(sb);}
void filesystems_freeze(bool freeze_all){ void *freeze_all_ptr = NULL;
if (freeze_all) freeze_all_ptr = &freeze_all; __iterate_supers(filesystems_freeze_callback, freeze_all_ptr, SUPER_ITER_UNLOCKED | SUPER_ITER_REVERSE);}
static void filesystems_thaw_callback(struct super_block *sb, void *unused){ if (!sb->s_op->freeze_fs && !sb->s_op->freeze_super) return;
if (!get_active_super(sb)) return;
if (sb->s_op->thaw_super) sb->s_op->thaw_super(sb, FREEZE_EXCL | FREEZE_HOLDER_KERNEL, filesystems_freeze_ptr); else thaw_super(sb, FREEZE_EXCL | FREEZE_HOLDER_KERNEL, filesystems_freeze_ptr);
deactivate_super(sb);}
void filesystems_thaw(void){ __iterate_supers(filesystems_thaw_callback, NULL, SUPER_ITER_UNLOCKED);}
static DEFINE_IDA(unnamed_dev_ida);
/** * get_anon_bdev - Allocate a block device for filesystems which don't have one. * @p: Pointer to a dev_t. * * Filesystems which don't use real block devices can call this function * to allocate a virtual block device. * * Context: Any context. Frequently called while holding sb_lock. * Return: 0 on success, -EMFILE if there are no anonymous bdevs left * or -ENOMEM if memory allocation failed. */int get_anon_bdev(dev_t *p){ int dev;
/* * Many userspace utilities consider an FSID of 0 invalid. * Always return at least 1 from get_anon_bdev. */ dev = ida_alloc_range(&unnamed_dev_ida, 1, (1 << MINORBITS) - 1, GFP_ATOMIC); if (dev == -ENOSPC) dev = -EMFILE; if (dev < 0) return dev;
*p = MKDEV(0, dev); return 0;}EXPORT_SYMBOL(get_anon_bdev);
void free_anon_bdev(dev_t dev){ ida_free(&unnamed_dev_ida, MINOR(dev));}EXPORT_SYMBOL(free_anon_bdev);
int set_anon_super(struct super_block *s, void *data){ return get_anon_bdev(&s->s_dev);}EXPORT_SYMBOL(set_anon_super);
void kill_anon_super(struct super_block *sb){ dev_t dev = sb->s_dev; generic_shutdown_super(sb); kill_super_notify(sb); free_anon_bdev(dev);}EXPORT_SYMBOL(kill_anon_super);
int set_anon_super_fc(struct super_block *sb, struct fs_context *fc){ return set_anon_super(sb, NULL);}EXPORT_SYMBOL(set_anon_super_fc);
static int test_keyed_super(struct super_block *sb, struct fs_context *fc){ return sb->s_fs_info == fc->s_fs_info;}
static int test_single_super(struct super_block *s, struct fs_context *fc){ return 1;}
static int vfs_get_super(struct fs_context *fc, int (*test)(struct super_block *, struct fs_context *), int (*fill_super)(struct super_block *sb, struct fs_context *fc)){ struct super_block *sb; int err;
sb = sget_fc(fc, test, set_anon_super_fc); if (IS_ERR(sb)) return PTR_ERR(sb);
if (!sb->s_root) { err = fill_super(sb, fc); if (err) goto error;
sb->s_flags |= SB_ACTIVE; }
fc->root = dget(sb->s_root); return 0;
error: deactivate_locked_super(sb); return err;}
int get_tree_nodev(struct fs_context *fc, int (*fill_super)(struct super_block *sb, struct fs_context *fc)){ return vfs_get_super(fc, NULL, fill_super);}EXPORT_SYMBOL(get_tree_nodev);
int get_tree_single(struct fs_context *fc, int (*fill_super)(struct super_block *sb, struct fs_context *fc)){ return vfs_get_super(fc, test_single_super, fill_super);}EXPORT_SYMBOL(get_tree_single);
int get_tree_keyed(struct fs_context *fc, int (*fill_super)(struct super_block *sb, struct fs_context *fc), void *key){ fc->s_fs_info = key; return vfs_get_super(fc, test_keyed_super, fill_super);}EXPORT_SYMBOL(get_tree_keyed);
static int set_bdev_super(struct super_block *s, void *data){ s->s_dev = *(dev_t *)data; return 0;}
static int super_s_dev_set(struct super_block *s, struct fs_context *fc){ return set_bdev_super(s, fc->sget_key);}
static int super_s_dev_test(struct super_block *s, struct fs_context *fc){ return !(s->s_iflags & SB_I_RETIRED) && s->s_dev == *(dev_t *)fc->sget_key;}
/** * sget_dev - Find or create a superblock by device number * @fc: Filesystem context. * @dev: device number * * Find or create a superblock using the provided device number that * will be stored in fc->sget_key. * * If an extant superblock is matched, then that will be returned with * an elevated reference count that the caller must transfer or discard. * * If no match is made, a new superblock will be allocated and basic * initialisation will be performed (s_type, s_fs_info, s_id, s_dev will * be set). The superblock will be published and it will be returned in * a partially constructed state with SB_BORN and SB_ACTIVE as yet * unset. * * Return: an existing or newly created superblock on success, an error * pointer on failure. */struct super_block *sget_dev(struct fs_context *fc, dev_t dev){ fc->sget_key = &dev; return sget_fc(fc, super_s_dev_test, super_s_dev_set);}EXPORT_SYMBOL(sget_dev);
#ifdef CONFIG_BLOCK/* * Lock the superblock that is holder of the bdev. Returns the superblock * pointer if we successfully locked the superblock and it is alive. Otherwise * we return NULL and just unlock bdev->bd_holder_lock. * * The function must be called with bdev->bd_holder_lock and releases it. */static struct super_block *bdev_super_lock(struct block_device *bdev, bool excl) __releases(&bdev->bd_holder_lock){ struct super_block *sb = bdev->bd_holder; bool locked;
lockdep_assert_held(&bdev->bd_holder_lock); lockdep_assert_not_held(&sb->s_umount); lockdep_assert_not_held(&bdev->bd_disk->open_mutex);
/* Make sure sb doesn't go away from under us */ spin_lock(&sb_lock); sb->s_count++; spin_unlock(&sb_lock);
mutex_unlock(&bdev->bd_holder_lock);
locked = super_lock(sb, excl);
/* * If the superblock wasn't already SB_DYING then we hold * s_umount and can safely drop our temporary reference. */ put_super(sb);
if (!locked) return NULL;
if (!sb->s_root || !(sb->s_flags & SB_ACTIVE)) { super_unlock(sb, excl); return NULL; }
return sb;}
static void fs_bdev_mark_dead(struct block_device *bdev, bool surprise){ struct super_block *sb;
sb = bdev_super_lock(bdev, false); if (!sb) return;
if (sb->s_op->remove_bdev) { int ret;
ret = sb->s_op->remove_bdev(sb, bdev); if (!ret) { super_unlock_shared(sb); return; } /* Fallback to shutdown. */ }
if (!surprise) sync_filesystem(sb); shrink_dcache_sb(sb); evict_inodes(sb); if (sb->s_op->shutdown) sb->s_op->shutdown(sb);
super_unlock_shared(sb);}
static void fs_bdev_sync(struct block_device *bdev){ struct super_block *sb;
sb = bdev_super_lock(bdev, false); if (!sb) return;
sync_filesystem(sb); super_unlock_shared(sb);}
static struct super_block *get_bdev_super(struct block_device *bdev){ bool active = false; struct super_block *sb;
sb = bdev_super_lock(bdev, true); if (sb) { active = atomic_inc_not_zero(&sb->s_active); super_unlock_excl(sb); } if (!active) return NULL; return sb;}
/** * fs_bdev_freeze - freeze owning filesystem of block device * @bdev: block device * * Freeze the filesystem that owns this block device if it is still * active. * * A filesystem that owns multiple block devices may be frozen from each * block device and won't be unfrozen until all block devices are * unfrozen. Each block device can only freeze the filesystem once as we * nest freezes for block devices in the block layer. * * Return: If the freeze was successful zero is returned. If the freeze * failed a negative error code is returned. */static int fs_bdev_freeze(struct block_device *bdev){ struct super_block *sb; int error = 0;
lockdep_assert_held(&bdev->bd_fsfreeze_mutex);
sb = get_bdev_super(bdev); if (!sb) return -EINVAL;
if (sb->s_op->freeze_super) error = sb->s_op->freeze_super(sb, FREEZE_MAY_NEST | FREEZE_HOLDER_USERSPACE, NULL); else error = freeze_super(sb, FREEZE_MAY_NEST | FREEZE_HOLDER_USERSPACE, NULL); if (!error) error = sync_blockdev(bdev); deactivate_super(sb); return error;}
/** * fs_bdev_thaw - thaw owning filesystem of block device * @bdev: block device * * Thaw the filesystem that owns this block device. * * A filesystem that owns multiple block devices may be frozen from each * block device and won't be unfrozen until all block devices are * unfrozen. Each block device can only freeze the filesystem once as we * nest freezes for block devices in the block layer. * * Return: If the thaw was successful zero is returned. If the thaw * failed a negative error code is returned. If this function * returns zero it doesn't mean that the filesystem is unfrozen * as it may have been frozen multiple times (kernel may hold a * freeze or might be frozen from other block devices). */static int fs_bdev_thaw(struct block_device *bdev){ struct super_block *sb; int error;
lockdep_assert_held(&bdev->bd_fsfreeze_mutex);
/* * The block device may have been frozen before it was claimed by a * filesystem. Concurrently another process might try to mount that * frozen block device and has temporarily claimed the block device for * that purpose causing a concurrent fs_bdev_thaw() to end up here. The * mounter is already about to abort mounting because they still saw an * elevanted bdev->bd_fsfreeze_count so get_bdev_super() will return * NULL in that case. */ sb = get_bdev_super(bdev); if (!sb) return -EINVAL;
if (sb->s_op->thaw_super) error = sb->s_op->thaw_super(sb, FREEZE_MAY_NEST | FREEZE_HOLDER_USERSPACE, NULL); else error = thaw_super(sb, FREEZE_MAY_NEST | FREEZE_HOLDER_USERSPACE, NULL); deactivate_super(sb); return error;}
const struct blk_holder_ops fs_holder_ops = { .mark_dead = fs_bdev_mark_dead, .sync = fs_bdev_sync, .freeze = fs_bdev_freeze, .thaw = fs_bdev_thaw,};EXPORT_SYMBOL_GPL(fs_holder_ops);
int setup_bdev_super(struct super_block *sb, int sb_flags, struct fs_context *fc){ blk_mode_t mode = sb_open_mode(sb_flags); struct file *bdev_file; struct block_device *bdev;
bdev_file = bdev_file_open_by_dev(sb->s_dev, mode, sb, &fs_holder_ops); if (IS_ERR(bdev_file)) { if (fc) errorf(fc, "%s: Can't open blockdev", fc->source); return PTR_ERR(bdev_file); } bdev = file_bdev(bdev_file);
/* * This really should be in blkdev_get_by_dev, but right now can't due * to legacy issues that require us to allow opening a block device node * writable from userspace even for a read-only block device. */ if ((mode & BLK_OPEN_WRITE) && bdev_read_only(bdev)) { bdev_fput(bdev_file); return -EACCES; }
/* * It is enough to check bdev was not frozen before we set * s_bdev as freezing will wait until SB_BORN is set. */ if (atomic_read(&bdev->bd_fsfreeze_count) > 0) { if (fc) warnf(fc, "%pg: Can't mount, blockdev is frozen", bdev); bdev_fput(bdev_file); return -EBUSY; } spin_lock(&sb_lock); sb->s_bdev_file = bdev_file; sb->s_bdev = bdev; sb->s_bdi = bdi_get(bdev->bd_disk->bdi); if (bdev_stable_writes(bdev)) sb->s_iflags |= SB_I_STABLE_WRITES; spin_unlock(&sb_lock);
snprintf(sb->s_id, sizeof(sb->s_id), "%pg", bdev); shrinker_debugfs_rename(sb->s_shrink, "sb-%s:%s", sb->s_type->name, sb->s_id); sb_set_blocksize(sb, block_size(bdev)); return 0;}EXPORT_SYMBOL_GPL(setup_bdev_super);
/** * get_tree_bdev_flags - Get a superblock based on a single block device * @fc: The filesystem context holding the parameters * @fill_super: Helper to initialise a new superblock * @flags: GET_TREE_BDEV_* flags */int get_tree_bdev_flags(struct fs_context *fc, int (*fill_super)(struct super_block *sb, struct fs_context *fc), unsigned int flags){ struct super_block *s; int error = 0; dev_t dev;
if (!fc->source) return invalf(fc, "No source specified");
error = lookup_bdev(fc->source, &dev); if (error) { if (!(flags & GET_TREE_BDEV_QUIET_LOOKUP)) errorf(fc, "%s: Can't lookup blockdev", fc->source); return error; } fc->sb_flags |= SB_NOSEC; s = sget_dev(fc, dev); if (IS_ERR(s)) return PTR_ERR(s);
if (s->s_root) { /* Don't summarily change the RO/RW state. */ if ((fc->sb_flags ^ s->s_flags) & SB_RDONLY) { warnf(fc, "%pg: Can't mount, would change RO state", s->s_bdev); deactivate_locked_super(s); return -EBUSY; } } else { error = setup_bdev_super(s, fc->sb_flags, fc); if (!error) error = fill_super(s, fc); if (error) { deactivate_locked_super(s); return error; } s->s_flags |= SB_ACTIVE; }
BUG_ON(fc->root); fc->root = dget(s->s_root); return 0;}EXPORT_SYMBOL_GPL(get_tree_bdev_flags);
/** * get_tree_bdev - Get a superblock based on a single block device * @fc: The filesystem context holding the parameters * @fill_super: Helper to initialise a new superblock */int get_tree_bdev(struct fs_context *fc, int (*fill_super)(struct super_block *, struct fs_context *)){ return get_tree_bdev_flags(fc, fill_super, 0);}EXPORT_SYMBOL(get_tree_bdev);
void kill_block_super(struct super_block *sb){ struct block_device *bdev = sb->s_bdev;
generic_shutdown_super(sb); if (bdev) { sync_blockdev(bdev); bdev_fput(sb->s_bdev_file); }}
EXPORT_SYMBOL(kill_block_super);#endif
/** * vfs_get_tree - Get the mountable root * @fc: The superblock configuration context. * * The filesystem is invoked to get or create a superblock which can then later * be used for mounting. The filesystem places a pointer to the root to be * used for mounting in @fc->root. */int vfs_get_tree(struct fs_context *fc){ struct super_block *sb; int error;
if (fc->root) return -EBUSY;
/* Get the mountable root in fc->root, with a ref on the root and a ref * on the superblock. */ error = fc->ops->get_tree(fc); if (error < 0) return error;
if (!fc->root) { pr_err("Filesystem %s get_tree() didn't set fc->root, returned %i\n", fc->fs_type->name, error); /* We don't know what the locking state of the superblock is - * if there is a superblock. */ BUG(); }
sb = fc->root->d_sb; WARN_ON(!sb->s_bdi);
/* * super_wake() contains a memory barrier which also care of * ordering for super_cache_count(). We place it before setting * SB_BORN as the data dependency between the two functions is * the superblock structure contents that we just set up, not * the SB_BORN flag. */ super_wake(sb, SB_BORN);
error = security_sb_set_mnt_opts(sb, fc->security, 0, NULL); if (unlikely(error)) { fc_drop_locked(fc); return error; }
/* * filesystems should never set s_maxbytes larger than MAX_LFS_FILESIZE * but s_maxbytes was an unsigned long long for many releases. Throw * this warning for a little while to try and catch filesystems that * violate this rule. */ WARN((sb->s_maxbytes < 0), "%s set sb->s_maxbytes to " "negative value (%lld)\n", fc->fs_type->name, sb->s_maxbytes);
return 0;}EXPORT_SYMBOL(vfs_get_tree);
/* * Setup private BDI for given superblock. It gets automatically cleaned up * in generic_shutdown_super(). */int super_setup_bdi_name(struct super_block *sb, char *fmt, ...){ struct backing_dev_info *bdi; int err; va_list args;
bdi = bdi_alloc(NUMA_NO_NODE); if (!bdi) return -ENOMEM;
va_start(args, fmt); err = bdi_register_va(bdi, fmt, args); va_end(args); if (err) { bdi_put(bdi); return err; } WARN_ON(sb->s_bdi != &noop_backing_dev_info); sb->s_bdi = bdi; sb->s_iflags |= SB_I_PERSB_BDI;
return 0;}EXPORT_SYMBOL(super_setup_bdi_name);
/* * Setup private BDI for given superblock. I gets automatically cleaned up * in generic_shutdown_super(). */int super_setup_bdi(struct super_block *sb){ static atomic_long_t bdi_seq = ATOMIC_LONG_INIT(0);
return super_setup_bdi_name(sb, "%.28s-%ld", sb->s_type->name, atomic_long_inc_return(&bdi_seq));}EXPORT_SYMBOL(super_setup_bdi);
/** * sb_wait_write - wait until all writers to given file system finish * @sb: the super for which we wait * @level: type of writers we wait for (normal vs page fault) * * This function waits until there are no writers of given type to given file * system. */static void sb_wait_write(struct super_block *sb, int level){ percpu_down_write(sb->s_writers.rw_sem + level-1);}
/* * We are going to return to userspace and forget about these locks, the * ownership goes to the caller of thaw_super() which does unlock(). */static void lockdep_sb_freeze_release(struct super_block *sb){ int level;
for (level = SB_FREEZE_LEVELS - 1; level >= 0; level--) percpu_rwsem_release(sb->s_writers.rw_sem + level, _THIS_IP_);}
/* * Tell lockdep we are holding these locks before we call ->unfreeze_fs(sb). */static void lockdep_sb_freeze_acquire(struct super_block *sb){ int level;
for (level = 0; level < SB_FREEZE_LEVELS; ++level) percpu_rwsem_acquire(sb->s_writers.rw_sem + level, 0, _THIS_IP_);}
static void sb_freeze_unlock(struct super_block *sb, int level){ for (level--; level >= 0; level--) percpu_up_write(sb->s_writers.rw_sem + level);}
static int wait_for_partially_frozen(struct super_block *sb){ int ret = 0;
do { unsigned short old = sb->s_writers.frozen;
up_write(&sb->s_umount); ret = wait_var_event_killable(&sb->s_writers.frozen, sb->s_writers.frozen != old); down_write(&sb->s_umount); } while (ret == 0 && sb->s_writers.frozen != SB_UNFROZEN && sb->s_writers.frozen != SB_FREEZE_COMPLETE);
return ret;}
#define FREEZE_HOLDERS (FREEZE_HOLDER_KERNEL | FREEZE_HOLDER_USERSPACE)#define FREEZE_FLAGS (FREEZE_HOLDERS | FREEZE_MAY_NEST | FREEZE_EXCL)
static inline int freeze_inc(struct super_block *sb, enum freeze_holder who){ WARN_ON_ONCE((who & ~FREEZE_FLAGS)); WARN_ON_ONCE(hweight32(who & FREEZE_HOLDERS) > 1);
if (who & FREEZE_HOLDER_KERNEL) ++sb->s_writers.freeze_kcount; if (who & FREEZE_HOLDER_USERSPACE) ++sb->s_writers.freeze_ucount; return sb->s_writers.freeze_kcount + sb->s_writers.freeze_ucount;}
static inline int freeze_dec(struct super_block *sb, enum freeze_holder who){ WARN_ON_ONCE((who & ~FREEZE_FLAGS)); WARN_ON_ONCE(hweight32(who & FREEZE_HOLDERS) > 1);
if ((who & FREEZE_HOLDER_KERNEL) && sb->s_writers.freeze_kcount) --sb->s_writers.freeze_kcount; if ((who & FREEZE_HOLDER_USERSPACE) && sb->s_writers.freeze_ucount) --sb->s_writers.freeze_ucount; return sb->s_writers.freeze_kcount + sb->s_writers.freeze_ucount;}
static inline bool may_freeze(struct super_block *sb, enum freeze_holder who, const void *freeze_owner){ lockdep_assert_held(&sb->s_umount);
WARN_ON_ONCE((who & ~FREEZE_FLAGS)); WARN_ON_ONCE(hweight32(who & FREEZE_HOLDERS) > 1);
if (who & FREEZE_EXCL) { if (WARN_ON_ONCE(!(who & FREEZE_HOLDER_KERNEL))) return false; if (WARN_ON_ONCE(who & ~(FREEZE_EXCL | FREEZE_HOLDER_KERNEL))) return false; if (WARN_ON_ONCE(!freeze_owner)) return false; /* This freeze already has a specific owner. */ if (sb->s_writers.freeze_owner) return false; /* * This is already frozen multiple times so we're just * going to take a reference count and mark the freeze as * being owned by the caller. */ if (sb->s_writers.freeze_kcount + sb->s_writers.freeze_ucount) sb->s_writers.freeze_owner = freeze_owner; return true; }
if (who & FREEZE_HOLDER_KERNEL) return (who & FREEZE_MAY_NEST) || sb->s_writers.freeze_kcount == 0; if (who & FREEZE_HOLDER_USERSPACE) return (who & FREEZE_MAY_NEST) || sb->s_writers.freeze_ucount == 0; return false;}
static inline bool may_unfreeze(struct super_block *sb, enum freeze_holder who, const void *freeze_owner){ lockdep_assert_held(&sb->s_umount);
WARN_ON_ONCE((who & ~FREEZE_FLAGS)); WARN_ON_ONCE(hweight32(who & FREEZE_HOLDERS) > 1);
if (who & FREEZE_EXCL) { if (WARN_ON_ONCE(!(who & FREEZE_HOLDER_KERNEL))) return false; if (WARN_ON_ONCE(who & ~(FREEZE_EXCL | FREEZE_HOLDER_KERNEL))) return false; if (WARN_ON_ONCE(!freeze_owner)) return false; if (WARN_ON_ONCE(sb->s_writers.freeze_kcount == 0)) return false; /* This isn't exclusively frozen. */ if (!sb->s_writers.freeze_owner) return false; /* This isn't exclusively frozen by us. */ if (sb->s_writers.freeze_owner != freeze_owner) return false; /* * This is still frozen multiple times so we're just * going to drop our reference count and undo our * exclusive freeze. */ if ((sb->s_writers.freeze_kcount + sb->s_writers.freeze_ucount) > 1) sb->s_writers.freeze_owner = NULL; return true; }
if (who & FREEZE_HOLDER_KERNEL) { /* * Someone's trying to steal the reference belonging to * @sb->s_writers.freeze_owner. */ if (sb->s_writers.freeze_kcount == 1 && sb->s_writers.freeze_owner) return false; return sb->s_writers.freeze_kcount > 0; }
if (who & FREEZE_HOLDER_USERSPACE) return sb->s_writers.freeze_ucount > 0;
return false;}
/** * freeze_super - lock the filesystem and force it into a consistent state * @sb: the super to lock * @who: context that wants to freeze * @freeze_owner: owner of the freeze * * Syncs the super to make sure the filesystem is consistent and calls the fs's * freeze_fs. Subsequent calls to this without first thawing the fs may return * -EBUSY. * * @who should be: * * %FREEZE_HOLDER_USERSPACE if userspace wants to freeze the fs; * * %FREEZE_HOLDER_KERNEL if the kernel wants to freeze the fs. * * %FREEZE_MAY_NEST whether nesting freeze and thaw requests is allowed. * * The @who argument distinguishes between the kernel and userspace trying to * freeze the filesystem. Although there cannot be multiple kernel freezes or * multiple userspace freezes in effect at any given time, the kernel and * userspace can both hold a filesystem frozen. The filesystem remains frozen * until there are no kernel or userspace freezes in effect. * * A filesystem may hold multiple devices and thus a filesystems may be * frozen through the block layer via multiple block devices. In this * case the request is marked as being allowed to nest by passing * FREEZE_MAY_NEST. The filesystem remains frozen until all block * devices are unfrozen. If multiple freezes are attempted without * FREEZE_MAY_NEST -EBUSY will be returned. * * During this function, sb->s_writers.frozen goes through these values: * * SB_UNFROZEN: File system is normal, all writes progress as usual. * * SB_FREEZE_WRITE: The file system is in the process of being frozen. New * writes should be blocked, though page faults are still allowed. We wait for * all writes to complete and then proceed to the next stage. * * SB_FREEZE_PAGEFAULT: Freezing continues. Now also page faults are blocked * but internal fs threads can still modify the filesystem (although they * should not dirty new pages or inodes), writeback can run etc. After waiting * for all running page faults we sync the filesystem which will clean all * dirty pages and inodes (no new dirty pages or inodes can be created when * sync is running). * * SB_FREEZE_FS: The file system is frozen. Now all internal sources of fs * modification are blocked (e.g. XFS preallocation truncation on inode * reclaim). This is usually implemented by blocking new transactions for * filesystems that have them and need this additional guard. After all * internal writers are finished we call ->freeze_fs() to finish filesystem * freezing. Then we transition to SB_FREEZE_COMPLETE state. This state is * mostly auxiliary for filesystems to verify they do not modify frozen fs. * * sb->s_writers.frozen is protected by sb->s_umount. * * Return: If the freeze was successful zero is returned. If the freeze * failed a negative error code is returned. */int freeze_super(struct super_block *sb, enum freeze_holder who, const void *freeze_owner){ int ret;
if (!super_lock_excl(sb)) { WARN_ON_ONCE("Dying superblock while freezing!"); return -EINVAL; } atomic_inc(&sb->s_active);
retry: if (sb->s_writers.frozen == SB_FREEZE_COMPLETE) { if (may_freeze(sb, who, freeze_owner)) ret = !!WARN_ON_ONCE(freeze_inc(sb, who) == 1); else ret = -EBUSY; /* All freezers share a single active reference. */ deactivate_locked_super(sb); return ret; }
if (sb->s_writers.frozen != SB_UNFROZEN) { ret = wait_for_partially_frozen(sb); if (ret) { deactivate_locked_super(sb); return ret; }
goto retry; }
if (sb_rdonly(sb)) { /* Nothing to do really... */ WARN_ON_ONCE(freeze_inc(sb, who) > 1); sb->s_writers.freeze_owner = freeze_owner; sb->s_writers.frozen = SB_FREEZE_COMPLETE; wake_up_var(&sb->s_writers.frozen); super_unlock_excl(sb); return 0; }
sb->s_writers.frozen = SB_FREEZE_WRITE; /* Release s_umount to preserve sb_start_write -> s_umount ordering */ super_unlock_excl(sb); sb_wait_write(sb, SB_FREEZE_WRITE); __super_lock_excl(sb);
/* Now we go and block page faults... */ sb->s_writers.frozen = SB_FREEZE_PAGEFAULT; sb_wait_write(sb, SB_FREEZE_PAGEFAULT);
/* All writers are done so after syncing there won't be dirty data */ ret = sync_filesystem(sb); if (ret) { sb->s_writers.frozen = SB_UNFROZEN; sb_freeze_unlock(sb, SB_FREEZE_PAGEFAULT); wake_up_var(&sb->s_writers.frozen); deactivate_locked_super(sb); return ret; }
/* Now wait for internal filesystem counter */ sb->s_writers.frozen = SB_FREEZE_FS; sb_wait_write(sb, SB_FREEZE_FS);
if (sb->s_op->freeze_fs) { ret = sb->s_op->freeze_fs(sb); if (ret) { printk(KERN_ERR "VFS:Filesystem freeze failed\n"); sb->s_writers.frozen = SB_UNFROZEN; sb_freeze_unlock(sb, SB_FREEZE_FS); wake_up_var(&sb->s_writers.frozen); deactivate_locked_super(sb); return ret; } } /* * For debugging purposes so that fs can warn if it sees write activity * when frozen is set to SB_FREEZE_COMPLETE, and for thaw_super(). */ WARN_ON_ONCE(freeze_inc(sb, who) > 1); sb->s_writers.freeze_owner = freeze_owner; sb->s_writers.frozen = SB_FREEZE_COMPLETE; wake_up_var(&sb->s_writers.frozen); lockdep_sb_freeze_release(sb); super_unlock_excl(sb); return 0;}EXPORT_SYMBOL(freeze_super);
/* * Undoes the effect of a freeze_super_locked call. If the filesystem is * frozen both by userspace and the kernel, a thaw call from either source * removes that state without releasing the other state or unlocking the * filesystem. */static int thaw_super_locked(struct super_block *sb, enum freeze_holder who, const void *freeze_owner){ int error = -EINVAL;
if (sb->s_writers.frozen != SB_FREEZE_COMPLETE) goto out_unlock;
if (!may_unfreeze(sb, who, freeze_owner)) goto out_unlock;
/* * All freezers share a single active reference. * So just unlock in case there are any left. */ if (freeze_dec(sb, who)) goto out_unlock;
if (sb_rdonly(sb)) { sb->s_writers.frozen = SB_UNFROZEN; sb->s_writers.freeze_owner = NULL; wake_up_var(&sb->s_writers.frozen); goto out_deactivate; }
lockdep_sb_freeze_acquire(sb);
if (sb->s_op->unfreeze_fs) { error = sb->s_op->unfreeze_fs(sb); if (error) { pr_err("VFS: Filesystem thaw failed\n"); freeze_inc(sb, who); lockdep_sb_freeze_release(sb); goto out_unlock; } }
sb->s_writers.frozen = SB_UNFROZEN; sb->s_writers.freeze_owner = NULL; wake_up_var(&sb->s_writers.frozen); sb_freeze_unlock(sb, SB_FREEZE_FS);out_deactivate: deactivate_locked_super(sb); return 0;
out_unlock: super_unlock_excl(sb); return error;}
/** * thaw_super -- unlock filesystem * @sb: the super to thaw * @who: context that wants to freeze * @freeze_owner: owner of the freeze * * Unlocks the filesystem and marks it writeable again after freeze_super() * if there are no remaining freezes on the filesystem. * * @who should be: * * %FREEZE_HOLDER_USERSPACE if userspace wants to thaw the fs; * * %FREEZE_HOLDER_KERNEL if the kernel wants to thaw the fs. * * %FREEZE_MAY_NEST whether nesting freeze and thaw requests is allowed * * A filesystem may hold multiple devices and thus a filesystems may * have been frozen through the block layer via multiple block devices. * The filesystem remains frozen until all block devices are unfrozen. */int thaw_super(struct super_block *sb, enum freeze_holder who, const void *freeze_owner){ if (!super_lock_excl(sb)) { WARN_ON_ONCE("Dying superblock while thawing!"); return -EINVAL; } return thaw_super_locked(sb, who, freeze_owner);}EXPORT_SYMBOL(thaw_super);
/* * Create workqueue for deferred direct IO completions. We allocate the * workqueue when it's first needed. This avoids creating workqueue for * filesystems that don't need it and also allows us to create the workqueue * late enough so the we can include s_id in the name of the workqueue. */int sb_init_dio_done_wq(struct super_block *sb){ struct workqueue_struct *old; struct workqueue_struct *wq = alloc_workqueue("dio/%s", WQ_MEM_RECLAIM | WQ_PERCPU, 0, sb->s_id); if (!wq) return -ENOMEM;
old = NULL; /* * This has to be atomic as more DIOs can race to create the workqueue */ if (!try_cmpxchg(&sb->s_dio_done_wq, &old, wq)) { /* Someone created workqueue before us? Free ours... */ destroy_workqueue(wq); } return 0;}EXPORT_SYMBOL_GPL(sb_init_dio_done_wq);