The patch below does not apply to the 6.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <stable@xxxxxxxxxxxxxxx>. To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.4.y git checkout FETCH_HEAD git cherry-pick -x 8a4a0b2a3eaf75ca8854f856ef29690c12b2f531 # <resolve conflicts, build, test, etc.> git commit -s git send-email --to '<stable@xxxxxxxxxxxxxxx>' --in-reply-to '2023071626-darkness-agony-ce5d@gregkh' --subject-prefix 'PATCH 6.4.y' HEAD^.. Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From 8a4a0b2a3eaf75ca8854f856ef29690c12b2f531 Mon Sep 17 00:00:00 2001 From: Filipe Manana <fdmanana@xxxxxxxx> Date: Mon, 19 Jun 2023 17:21:50 +0100 Subject: [PATCH] btrfs: fix race between quota disable and relocation If we disable quotas while we have a relocation of a metadata block group that has extents belonging to the quota root, we can cause the relocation to fail with -ENOENT. This is because relocation builds backref nodes for extents of the quota root and later needs to walk the backrefs and access the quota root - however if in between a task disables quotas, it results in deleting the quota root from the root tree (with btrfs_del_root(), called from btrfs_quota_disable(). This can be sporadically triggered by test case btrfs/255 from fstests: $ ./check btrfs/255 FSTYP -- btrfs PLATFORM -- Linux/x86_64 debian0 6.4.0-rc6-btrfs-next-134+ #1 SMP PREEMPT_DYNAMIC Thu Jun 15 11:59:28 WEST 2023 MKFS_OPTIONS -- /dev/sdc MOUNT_OPTIONS -- /dev/sdc /home/fdmanana/btrfs-tests/scratch_1 btrfs/255 6s ... _check_dmesg: something found in dmesg (see /home/fdmanana/git/hub/xfstests/results//btrfs/255.dmesg) - output mismatch (see /home/fdmanana/git/hub/xfstests/results//btrfs/255.out.bad) --- tests/btrfs/255.out 2023-03-02 21:47:53.876609426 +0000 +++ /home/fdmanana/git/hub/xfstests/results//btrfs/255.out.bad 2023-06-16 10:20:39.267563212 +0100 @@ -1,2 +1,4 @@ QA output created by 255 +ERROR: error during balancing '/home/fdmanana/btrfs-tests/scratch_1': No such file or directory +There may be more info in syslog - try dmesg | tail Silence is golden ... (Run 'diff -u /home/fdmanana/git/hub/xfstests/tests/btrfs/255.out /home/fdmanana/git/hub/xfstests/results//btrfs/255.out.bad' to see the entire diff) Ran: btrfs/255 Failures: btrfs/255 Failed 1 of 1 tests To fix this make the quota disable operation take the cleaner mutex, as relocation of a block group also takes this mutex. This is also what we do when deleting a subvolume/snapshot, we take the cleaner mutex in the cleaner kthread (at cleaner_kthread()) and then we call btrfs_del_root() at btrfs_drop_snapshot() while under the protection of the cleaner mutex. Fixes: bed92eae26cc ("Btrfs: qgroup implementation and prototypes") CC: stable@xxxxxxxxxxxxxxx # 5.4+ Signed-off-by: Filipe Manana <fdmanana@xxxxxxxx> Signed-off-by: David Sterba <dsterba@xxxxxxxx> diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c index f8735b31da16..da1f84a0eb29 100644 --- a/fs/btrfs/qgroup.c +++ b/fs/btrfs/qgroup.c @@ -1232,12 +1232,23 @@ int btrfs_quota_disable(struct btrfs_fs_info *fs_info) int ret = 0; /* - * We need to have subvol_sem write locked, to prevent races between - * concurrent tasks trying to disable quotas, because we will unlock - * and relock qgroup_ioctl_lock across BTRFS_FS_QUOTA_ENABLED changes. + * We need to have subvol_sem write locked to prevent races with + * snapshot creation. */ lockdep_assert_held_write(&fs_info->subvol_sem); + /* + * Lock the cleaner mutex to prevent races with concurrent relocation, + * because relocation may be building backrefs for blocks of the quota + * root while we are deleting the root. This is like dropping fs roots + * of deleted snapshots/subvolumes, we need the same protection. + * + * This also prevents races between concurrent tasks trying to disable + * quotas, because we will unlock and relock qgroup_ioctl_lock across + * BTRFS_FS_QUOTA_ENABLED changes. + */ + mutex_lock(&fs_info->cleaner_mutex); + mutex_lock(&fs_info->qgroup_ioctl_lock); if (!fs_info->quota_root) goto out; @@ -1319,6 +1330,7 @@ int btrfs_quota_disable(struct btrfs_fs_info *fs_info) btrfs_end_transaction(trans); else if (trans) ret = btrfs_end_transaction(trans); + mutex_unlock(&fs_info->cleaner_mutex); return ret; }
