From ea4e4cc263011910eb7c62f3bb4fa094a1573c61 Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Tue, 16 Jun 2026 13:58:14 +0200 Subject: block: allow making a block device unfreezable Add bdev_deny_freeze() and bdev_allow_freeze(), modeled on deny_write_access()/allow_write_access(). bd_fsfreeze_count becomes a signed counter: > 0 counts active freezes, < 0 counts deniers, and the two regimes are mutually exclusive. bdev_freeze() refuses with -EBUSY while a deny is held, and bdev_deny_freeze() refuses while the device is frozen. A filesystem that mutates a device's membership (a btrfs device add, remove or replace) denies freezing on the device for the duration, so a claim a freeze walk might act on is never added or torn down behind the freezer's back. The deny/allow helpers are a single atomic on bd_fsfreeze_count and take no lock, so they can be called while holding s_umount without inverting against bdev_freeze()'s bd_fsfreeze_mutex -> s_umount order. Reviewed-by: Jan Kara Link: https://patch.msgid.link/20260616-work-super-freeze_deny_upstream-v2-1-b3567c7f994b@kernel.org Signed-off-by: Christian Brauner (Amutable) --- include/linux/blk_types.h | 2 +- include/linux/blkdev.h | 2 ++ 2 files changed, 3 insertions(+), 1 deletion(-) (limited to 'include/linux') diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h index 8808ee76e73c..5a725a0cd35f 100644 --- a/include/linux/blk_types.h +++ b/include/linux/blk_types.h @@ -66,7 +66,7 @@ struct block_device { int bd_holders; struct kobject *bd_holder_dir; - atomic_t bd_fsfreeze_count; /* number of freeze requests */ + atomic_t bd_fsfreeze_count; /* >0 freeze requests, <0 freeze deniers */ struct mutex bd_fsfreeze_mutex; /* serialize freeze/thaw */ struct partition_meta_info *bd_meta_info; diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index 9213a5716f95..c419117be083 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -1837,6 +1837,8 @@ static inline int early_lookup_bdev(const char *pathname, dev_t *dev) int bdev_freeze(struct block_device *bdev); int bdev_thaw(struct block_device *bdev); +int bdev_deny_freeze(struct block_device *bdev); +void bdev_allow_freeze(struct block_device *bdev); void bdev_fput(struct file *bdev_file); struct io_comp_batch { -- cgit v1.2.3