From: Kaiwen Hu kevinhu@synology.com
commit 60021bd754c6ca0addc6817994f20290a321d8d6 upstream.
A subvolume with an active swapfile must not be deleted otherwise it would not be possible to deactivate it.
After the subvolume is deleted, we cannot swapoff the swapfile in this deleted subvolume because the path is unreachable. The swapfile is still active and holding references, the filesystem cannot be unmounted.
The test looks like this:
mkfs.btrfs -f $dev > /dev/null mount $dev $mnt
btrfs sub create $mnt/subvol touch $mnt/subvol/swapfile chmod 600 $mnt/subvol/swapfile chattr +C $mnt/subvol/swapfile dd if=/dev/zero of=$mnt/subvol/swapfile bs=1K count=4096 mkswap $mnt/subvol/swapfile swapon $mnt/subvol/swapfile
btrfs sub delete $mnt/subvol swapoff $mnt/subvol/swapfile # failed: No such file or directory swapoff --all
unmount $mnt # target is busy.
To prevent above issue, we simply check that whether the subvolume contains any active swapfile, and stop the deleting process. This behavior is like snapshot ioctl dealing with a swapfile.
CC: stable@vger.kernel.org # 5.4+ Reviewed-by: Robbie Ko robbieko@synology.com Reviewed-by: Qu Wenruo wqu@suse.com Reviewed-by: Filipe Manana fdmanana@suse.com Signed-off-by: Kaiwen Hu kevinhu@synology.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/btrfs/inode.c | 24 +++++++++++++++++++++++- 1 file changed, 23 insertions(+), 1 deletion(-)
--- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -4450,6 +4450,13 @@ int btrfs_delete_subvolume(struct inode dest->root_key.objectid); return -EPERM; } + if (atomic_read(&dest->nr_swapfiles)) { + spin_unlock(&dest->root_item_lock); + btrfs_warn(fs_info, + "attempt to delete subvolume %llu with active swapfile", + root->root_key.objectid); + return -EPERM; + } root_flags = btrfs_root_flags(&dest->root_item); btrfs_set_root_flags(&dest->root_item, root_flags | BTRFS_ROOT_SUBVOL_DEAD); @@ -10721,8 +10728,23 @@ static int btrfs_swap_activate(struct sw * set. We use this counter to prevent snapshots. We must increment it * before walking the extents because we don't want a concurrent * snapshot to run after we've already checked the extents. - */ + * + * It is possible that subvolume is marked for deletion but still not + * removed yet. To prevent this race, we check the root status before + * activating the swapfile. + */ + spin_lock(&root->root_item_lock); + if (btrfs_root_dead(root)) { + spin_unlock(&root->root_item_lock); + + btrfs_exclop_finish(fs_info); + btrfs_warn(fs_info, + "cannot activate swapfile because subvolume %llu is being deleted", + root->root_key.objectid); + return -EPERM; + } atomic_inc(&root->nr_swapfiles); + spin_unlock(&root->root_item_lock);
isize = ALIGN_DOWN(inode->i_size, fs_info->sectorsize);