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btrfs: do not clear read-only when adding sprout device

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If you follow the seed/sprout wiki, it suggests the following workflow:

btrfstune -S 1 seed_dev
mount seed_dev mnt
btrfs device add sprout_dev
mount -o remount,rw mnt

The first mount mounts the FS readonly, which results in not setting
BTRFS_FS_OPEN, and setting the readonly bit on the sb. The device add
somewhat surprisingly clears the readonly bit on the sb (though the
mount is still practically readonly, from the users perspective...).
Finally, the remount checks the readonly bit on the sb against the flag
and sees no change, so it does not run the code intended to run on
ro->rw transitions, leaving BTRFS_FS_OPEN unset.

As a result, when the cleaner_kthread runs, it sees no BTRFS_FS_OPEN and
does no work. This results in leaking deleted snapshots until we run out
of space.

I propose fixing it at the first departure from what feels reasonable:
when we clear the readonly bit on the sb during device add.

A new fstest I have written reproduces the bug and confirms the fix.

Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Boris Burkov <boris@bur.io>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Boris Burkov 2024-10-15 14:27:32 -07:00 committed by David Sterba
parent 4b5c1200f7
commit 70958a949d
1 changed files with 0 additions and 4 deletions
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4
fs/btrfs/volumes.c
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@ -2842,8 +2842,6 @@ int btrfs_init_new_device(struct btrfs_fs_info *fs_info, const char *device_path
set_blocksize(device->bdev_file, BTRFS_BDEV_BLOCKSIZE);
if (seeding_dev) {
btrfs_clear_sb_rdonly(sb);
/* GFP_KERNEL allocation must not be under device_list_mutex */
seed_devices = btrfs_init_sprout(fs_info);
if (IS_ERR(seed_devices)) {
@ -2986,8 +2984,6 @@ int btrfs_init_new_device(struct btrfs_fs_info *fs_info, const char *device_path
mutex_unlock(&fs_info->chunk_mutex);
mutex_unlock(&fs_info->fs_devices->device_list_mutex);
error_trans:
if (seeding_dev)
btrfs_set_sb_rdonly(sb);
if (trans)
btrfs_end_transaction(trans);
error_free_zone: