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commit 3324d0547861b16cf436d54abba7052e0c8aa9de upstream.
Sweet Tea spotted a race between subvolume deletion and snapshotting
that can result in the root item for the snapshot having the
BTRFS_ROOT_SUBVOL_DEAD flag set. The race is:
Thread 1 | Thread 2
----------------------------------------------|----------
btrfs_delete_subvolume |
btrfs_set_root_flags(BTRFS_ROOT_SUBVOL_DEAD)|
|btrfs_mksubvol
| down_read(subvol_sem)
| create_snapshot
| ...
| create_pending_snapshot
| copy root item from source
down_write(subvol_sem) |
This flag is only checked in send and swap activate, which this would
cause to fail mysteriously.
create_snapshot() now checks the root refs to reject a deleted
subvolume, so we can fix this by locking subvol_sem earlier so that the
BTRFS_ROOT_SUBVOL_DEAD flag and the root refs are updated atomically.
CC: stable@vger.kernel.org # 4.14+
Reported-by: Sweet Tea Dorminy <sweettea-kernel@dorminy.me>
Reviewed-by: Sweet Tea Dorminy <sweettea-kernel@dorminy.me>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Omar Sandoval <osandov@fb.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
3eaf00d2f8