btrfs: do not block on deleted bgs mutex in the cleaner

While running some stress tests I started getting hung task messages.
This is because the delete unused block groups code has to take the
delete_unused_bgs_mutex to do it's work, which is taken by balance to
make sure we don't delete block groups while we're balancing.

The problem is that balance can take a while, and so we were getting
hung task warnings.  We don't need to block and run these things, and
the cleaner is needed to do other work, so trylock on this mutex and
just bail if we can't acquire it right away.

Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.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 dda495b2a86213d767e6f89dfb6639bc19c81956..5fa6b3d540f4adff20806c475602e76f55b67986 100644 (file)
--- a/fs/btrfs/block-group.c
+++ b/fs/btrfs/block-group.c
@@ -1262,6 +1262,13 @@ void btrfs_delete_unused_bgs(struct btrfs_fs_info *fs_info)
        if (!test_bit(BTRFS_FS_OPEN, &fs_info->flags))
                return;
 
+       /*
+        * Long running balances can keep us blocked here for eternity, so
+        * simply skip deletion if we're unable to get the mutex.
+        */
+       if (!mutex_trylock(&fs_info->delete_unused_bgs_mutex))
+               return;
+
        spin_lock(&fs_info->unused_bgs_lock);
        while (!list_empty(&fs_info->unused_bgs)) {
                int trimming;
@@ -1281,8 +1288,6 @@ void btrfs_delete_unused_bgs(struct btrfs_fs_info *fs_info)
 
                btrfs_discard_cancel_work(&fs_info->discard_ctl, block_group);
 
-               mutex_lock(&fs_info->delete_unused_bgs_mutex);
-
                /* Don't want to race with allocators so take the groups_sem */
                down_write(&space_info->groups_sem);
 
@@ -1426,11 +1431,11 @@ void btrfs_delete_unused_bgs(struct btrfs_fs_info *fs_info)
 end_trans:
                btrfs_end_transaction(trans);
 next:
-               mutex_unlock(&fs_info->delete_unused_bgs_mutex);
                btrfs_put_block_group(block_group);
                spin_lock(&fs_info->unused_bgs_lock);
        }
        spin_unlock(&fs_info->unused_bgs_lock);
+       mutex_unlock(&fs_info->delete_unused_bgs_mutex);
        return;
 
 flip_async: