btrfs: zoned: mark relocation as writing

There is a hung_task issue with running generic/068 on an SMR
device. The hang occurs while a process is trying to thaw the
filesystem. The process is trying to take sb->s_umount to thaw the
FS. The lock is held by fsstress, which calls btrfs_sync_fs() and is
waiting for an ordered extent to finish. However, as the FS is frozen,
the ordered extents never finish.

Having an ordered extent while the FS is frozen is the root cause of
the hang. The ordered extent is initiated from btrfs_relocate_chunk()
which is called from btrfs_reclaim_bgs_work().

This commit adds sb_*_write() around btrfs_relocate_chunk() call
site. For the usual "btrfs balance" command, we already call it with
mnt_want_file() in btrfs_ioctl_balance().

Fixes: 18bb8bbf13c1 ("btrfs: zoned: automatically reclaim zones")
CC: stable@vger.kernel.org # 5.13+
Link: https://github.com/naota/linux/issues/56
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c
index 3113f6d7f335f95a36d379bf9ff4ee23751be7d1..c22d287e020b3d4f2a8afcffb6b9f4b84bae82a9 100644 (file)
--- a/fs/btrfs/block-group.c
+++ b/fs/btrfs/block-group.c
@@ -1522,8 +1522,12 @@ void btrfs_reclaim_bgs_work(struct work_struct *work)
        if (!test_bit(BTRFS_FS_OPEN, &fs_info->flags))
                return;
 
-       if (!btrfs_exclop_start(fs_info, BTRFS_EXCLOP_BALANCE))
+       sb_start_write(fs_info->sb);
+
+       if (!btrfs_exclop_start(fs_info, BTRFS_EXCLOP_BALANCE)) {
+               sb_end_write(fs_info->sb);
                return;
+       }
 
        /*
         * Long running balances can keep us blocked here for eternity, so
@@ -1531,6 +1535,7 @@ void btrfs_reclaim_bgs_work(struct work_struct *work)
         */
        if (!mutex_trylock(&fs_info->reclaim_bgs_lock)) {
                btrfs_exclop_finish(fs_info);
+               sb_end_write(fs_info->sb);
                return;
        }
 
@@ -1605,6 +1610,7 @@ next:
        spin_unlock(&fs_info->unused_bgs_lock);
        mutex_unlock(&fs_info->reclaim_bgs_lock);
        btrfs_exclop_finish(fs_info);
+       sb_end_write(fs_info->sb);
 }
 
 void btrfs_reclaim_bgs(struct btrfs_fs_info *fs_info)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index fa7fee09e39b8677ddc98c07ed35ecb124554137..5e3e13d4940b1877d056363981889f5ec8861379 100644 (file)
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -8304,10 +8304,12 @@ static int relocating_repair_kthread(void *data)
        target = cache->start;
        btrfs_put_block_group(cache);
 
+       sb_start_write(fs_info->sb);
        if (!btrfs_exclop_start(fs_info, BTRFS_EXCLOP_BALANCE)) {
                btrfs_info(fs_info,
                           "zoned: skip relocating block group %llu to repair: EBUSY",
                           target);
+               sb_end_write(fs_info->sb);
                return -EBUSY;
        }
 
@@ -8335,6 +8337,7 @@ out:
                btrfs_put_block_group(cache);
        mutex_unlock(&fs_info->reclaim_bgs_lock);
        btrfs_exclop_finish(fs_info);
+       sb_end_write(fs_info->sb);
 
        return ret;
 }