The old method of implementing block device freeze and thaw operations required us to rely on get_active_super() to walk the list of all superblocks on the system to find any superblock that might use the block device. This is wasteful and not very pleasant overall. Now that we can finally go straight from block device to owning superblock things become way simpler. Link: https://lore.kernel.org/r/20230927-vfs-super-freeze-v1-3-ecc36d9ab4d9@xxxxxxxxxx Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx> --- block/bdev.c | 62 +++++++++++------------ fs/super.c | 124 ++++++++++++++++++++++++++++++++++++---------- include/linux/blk_types.h | 2 +- 3 files changed, 128 insertions(+), 60 deletions(-) diff --git a/block/bdev.c b/block/bdev.c index a3e2af580a73..9deacd346192 100644 --- a/block/bdev.c +++ b/block/bdev.c @@ -222,31 +222,24 @@ EXPORT_SYMBOL(sync_blockdev_range); */ int bdev_freeze(struct block_device *bdev) { - struct super_block *sb; int error = 0; mutex_lock(&bdev->bd_fsfreeze_mutex); - if (++bdev->bd_fsfreeze_count > 1) - goto done; - - sb = get_active_super(bdev); - if (!sb) - goto sync; - if (sb->s_op->freeze_super) - error = sb->s_op->freeze_super(sb, FREEZE_HOLDER_USERSPACE); - else - error = freeze_super(sb, FREEZE_HOLDER_USERSPACE); - deactivate_super(sb); - if (error) { - bdev->bd_fsfreeze_count--; - goto done; + if (atomic_inc_return(&bdev->bd_fsfreeze_count) > 1) { + mutex_unlock(&bdev->bd_fsfreeze_mutex); + return 0; + } + + mutex_lock(&bdev->bd_holder_lock); + if (bdev->bd_holder_ops && bdev->bd_holder_ops->freeze) { + error = bdev->bd_holder_ops->freeze(bdev); + lockdep_assert_not_held(&bdev->bd_holder_lock); + } else { + mutex_unlock(&bdev->bd_holder_lock); + error = sync_blockdev(bdev); } - bdev->bd_fsfreeze_sb = sb; -sync: - error = sync_blockdev(bdev); -done: mutex_unlock(&bdev->bd_fsfreeze_mutex); return error; } @@ -262,29 +255,30 @@ EXPORT_SYMBOL(bdev_freeze); */ int bdev_thaw(struct block_device *bdev) { - struct super_block *sb; - int error = -EINVAL; + int error = -EINVAL, nr_freeze; mutex_lock(&bdev->bd_fsfreeze_mutex); - if (!bdev->bd_fsfreeze_count) + + /* + * If this returns < 0 it means that @bd_fsfreeze_count was + * already 0 and no decrement was performed. + */ + nr_freeze = atomic_dec_if_positive(&bdev->bd_fsfreeze_count); + if (nr_freeze < 0) goto out; error = 0; - if (--bdev->bd_fsfreeze_count > 0) + if (nr_freeze > 0) goto out; - sb = bdev->bd_fsfreeze_sb; - if (!sb) - goto out; + mutex_lock(&bdev->bd_holder_lock); + if (bdev->bd_holder_ops && bdev->bd_holder_ops->thaw) { + error = bdev->bd_holder_ops->thaw(bdev); + lockdep_assert_not_held(&bdev->bd_holder_lock); + } else { + mutex_unlock(&bdev->bd_holder_lock); + } - if (sb->s_op->thaw_super) - error = sb->s_op->thaw_super(sb, FREEZE_HOLDER_USERSPACE); - else - error = thaw_super(sb, FREEZE_HOLDER_USERSPACE); - if (error) - bdev->bd_fsfreeze_count++; - else - bdev->bd_fsfreeze_sb = NULL; out: mutex_unlock(&bdev->bd_fsfreeze_mutex); return error; diff --git a/fs/super.c b/fs/super.c index b224182f2440..ee0795ce09c7 100644 --- a/fs/super.c +++ b/fs/super.c @@ -1430,14 +1430,8 @@ struct super_block *sget_dev(struct fs_context *fc, dev_t dev) 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_shared(struct block_device *bdev) + +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; @@ -1451,18 +1445,37 @@ static struct super_block *bdev_super_lock_shared(struct block_device *bdev) spin_lock(&sb_lock); sb->s_count++; spin_unlock(&sb_lock); + mutex_unlock(&bdev->bd_holder_lock); - locked = super_lock_shared(sb); - if (!locked || !sb->s_root || !(sb->s_flags & SB_ACTIVE)) { - put_super(sb); + locked = super_lock(sb, excl); + put_super(sb); + if (!locked) + return NULL; + + return sb; +} + +/* + * 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_shared(struct block_device *bdev) +{ + struct super_block *sb; + + sb = bdev_super_lock(bdev, false); + if (!sb) + return NULL; + + if (!sb->s_root || !(sb->s_flags & SB_ACTIVE)) { + super_unlock_shared(sb); return NULL; } - /* - * The superblock is active and we hold s_umount, we can drop our - * temporary reference now. - */ - put_super(sb); + return sb; } @@ -1495,9 +1508,76 @@ static void fs_bdev_sync(struct block_device *bdev) 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; +} + +static int fs_bdev_freeze(struct block_device *bdev) +{ + struct super_block *sb; + int error = 0; + + lockdep_assert_held(&bdev->bd_fsfreeze_mutex); + + if (WARN_ON_ONCE(unlikely(!bdev->bd_holder))) + return -EINVAL; + + sb = get_bdev_super(bdev); + if (!sb) + return -EINVAL; + + if (sb->s_op->freeze_super) + error = sb->s_op->freeze_super(sb, FREEZE_HOLDER_USERSPACE); + else + error = freeze_super(sb, FREEZE_HOLDER_USERSPACE); + if (error) + atomic_dec(&bdev->bd_fsfreeze_count); + if (!error) + error = sync_blockdev(bdev); + deactivate_super(sb); + return error; +} + +static int fs_bdev_thaw(struct block_device *bdev) +{ + struct super_block *sb; + int error; + + lockdep_assert_held(&bdev->bd_fsfreeze_mutex); + + if (WARN_ON_ONCE(unlikely(!bdev->bd_holder))) + return -EINVAL; + + sb = get_bdev_super(bdev); + if (WARN_ON_ONCE(!sb)) + return -EINVAL; + + if (sb->s_op->thaw_super) + error = sb->s_op->thaw_super(sb, FREEZE_HOLDER_USERSPACE); + else + error = thaw_super(sb, FREEZE_HOLDER_USERSPACE); + if (error) + atomic_inc(&bdev->bd_fsfreeze_count); + 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); @@ -1527,15 +1607,10 @@ int setup_bdev_super(struct super_block *sb, int sb_flags, } /* - * Until SB_BORN flag is set, there can be no active superblock - * references and thus no filesystem freezing. get_active_super() will - * just loop waiting for SB_BORN so even bdev_freeze() cannot proceed. - * - * It is enough to check bdev was not frozen before we set s_bdev. + * It is enough to check bdev was not frozen before we set + * s_bdev as freezing will wait until SB_BORN is set. */ - mutex_lock(&bdev->bd_fsfreeze_mutex); - if (bdev->bd_fsfreeze_count > 0) { - mutex_unlock(&bdev->bd_fsfreeze_mutex); + if (atomic_read(&bdev->bd_fsfreeze_count) > 0) { if (fc) warnf(fc, "%pg: Can't mount, blockdev is frozen", bdev); bdev_release(bdev_handle); @@ -1548,7 +1623,6 @@ int setup_bdev_super(struct super_block *sb, int sb_flags, if (bdev_stable_writes(bdev)) sb->s_iflags |= SB_I_STABLE_WRITES; spin_unlock(&sb_lock); - mutex_unlock(&bdev->bd_fsfreeze_mutex); snprintf(sb->s_id, sizeof(sb->s_id), "%pg", bdev); shrinker_debugfs_rename(&sb->s_shrink, "sb-%s:%s", sb->s_type->name, diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h index d5c5e59ddbd2..88e1848b0869 100644 --- a/include/linux/blk_types.h +++ b/include/linux/blk_types.h @@ -57,7 +57,7 @@ struct block_device { const struct blk_holder_ops *bd_holder_ops; struct mutex bd_holder_lock; /* The counter of freeze processes */ - int bd_fsfreeze_count; + atomic_t bd_fsfreeze_count; int bd_holders; struct kobject *bd_holder_dir; -- 2.34.1
