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authorFilipe Manana <fdmanana@suse.com>2023-06-19 17:21:50 +0100
committerDavid Sterba <dsterba@suse.com>2023-06-19 20:29:25 +0200
commit8a4a0b2a3eaf75ca8854f856ef29690c12b2f531 (patch)
tree6c77ed5162acca0343b1d70f8bcb99bd39d003a8 /fs/btrfs/qgroup.c
parent08eb2ad9db0a1f65786ab9133d6fe1683c0647c8 (diff)
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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@vger.kernel.org # 5.4+ Signed-off-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
Diffstat (limited to 'fs/btrfs/qgroup.c')
-rw-r--r--fs/btrfs/qgroup.c18
1 files changed, 15 insertions, 3 deletions
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 @@ out:
btrfs_end_transaction(trans);
else if (trans)
ret = btrfs_end_transaction(trans);
+ mutex_unlock(&fs_info->cleaner_mutex);
return ret;
}