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From: Josef Bacik <josef@toxicpanda.com>
To: linux-btrfs@vger.kernel.org, kernel-team@fb.com
Cc: Nikolay Borisov <nborisov@suse.com>
Subject: [PATCH v5 1/8] btrfs: do not block on deleted bgs mutex in the cleaner
Date: Fri, 18 Dec 2020 14:24:19 -0500	[thread overview]
Message-ID: <0c1995f8b35b44ceb0043ab2303b9e02a5517a46.1608319304.git.josef@toxicpanda.com> (raw)
In-Reply-To: <cover.1608319304.git.josef@toxicpanda.com>

While running some stress tests I started getting hung task messages.
This is because the delete unused bg's 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 a 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>
---
 fs/btrfs/block-group.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c
index 52f2198d44c9..f61e275bd792 100644
--- a/fs/btrfs/block-group.c
+++ b/fs/btrfs/block-group.c
@@ -1254,6 +1254,13 @@ 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;
@@ -1273,8 +1280,6 @@ 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);
 
@@ -1420,11 +1425,11 @@ 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:
-- 
2.26.2


  reply	other threads:[~2020-12-18 19:25 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-18 19:24 [PATCH v5 0/8] A variety of lock contention fixes Josef Bacik
2020-12-18 19:24 ` Josef Bacik [this message]
2020-12-18 19:24 ` [PATCH v5 2/8] btrfs: only let one thread pre-flush delayed refs in commit Josef Bacik
2021-01-08 16:01   ` David Sterba
2021-01-11  8:33     ` Nikolay Borisov
2021-01-11 21:50       ` David Sterba
2021-01-12  9:17         ` Nikolay Borisov
2021-01-26 17:36           ` David Sterba
2020-12-18 19:24 ` [PATCH v5 3/8] btrfs: delayed refs pre-flushing should only run the heads we have Josef Bacik
2020-12-18 19:24 ` [PATCH v5 4/8] btrfs: only run delayed refs once before committing Josef Bacik
2020-12-18 19:24 ` [PATCH v5 5/8] btrfs: move delayed ref flushing for qgroup into qgroup helper Josef Bacik
2020-12-18 19:24 ` [PATCH v5 6/8] btrfs: remove bogus BUG_ON in alloc_reserved_tree_block Josef Bacik
2020-12-18 19:24 ` [PATCH v5 7/8] btrfs: stop running all delayed refs during snapshot Josef Bacik
2020-12-18 19:24 ` [PATCH v5 8/8] btrfs: run delayed refs less often in commit_cowonly_roots Josef Bacik
2021-01-26 17:51 ` [PATCH v5 0/8] A variety of lock contention fixes David Sterba

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