linux-kernel - [PATCH 5.13 032/351] btrfs: dont block if we cant acquire the reclaim lock

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Message-Id: <20210719144945.592297152@linuxfoundation.org>
Date:   Mon, 19 Jul 2021 16:49:38 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Johannes Thumshirn <johannes.thumshirn@....com>,
        David Sterba <dsterba@...e.com>
Subject: [PATCH 5.13 032/351] btrfs: dont block if we cant acquire the reclaim lock

From: Johannes Thumshirn <johannes.thumshirn@....com>

commit 9cc0b837e14ae913581ec1ea6e979a738f71b0fd upstream.

If we can't acquire the reclaim_bgs_lock on block group reclaim, we
block until it is free. This can potentially stall for a long time.

While reclaim of block groups is necessary for a good user experience on
a zoned file system, there still is no need to block as it is best
effort only, just like when we're deleting unused block groups.

CC: stable@...r.kernel.org # 5.13
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@....com>
Reviewed-by: David Sterba <dsterba@...e.com>
Signed-off-by: David Sterba <dsterba@...e.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 fs/btrfs/block-group.c |   10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

--- a/fs/btrfs/block-group.c
+++ b/fs/btrfs/block-group.c
@@ -1499,7 +1499,15 @@ void btrfs_reclaim_bgs_work(struct work_
 	if (!btrfs_exclop_start(fs_info, BTRFS_EXCLOP_BALANCE))
 		return;
 
-	mutex_lock(&fs_info->reclaim_bgs_lock);
+	/*
+	 * Long running balances can keep us blocked here for eternity, so
+	 * simply skip reclaim if we're unable to get the mutex.
+	 */
+	if (!mutex_trylock(&fs_info->reclaim_bgs_lock)) {
+		btrfs_exclop_finish(fs_info);
+		return;
+	}
+
 	spin_lock(&fs_info->unused_bgs_lock);
 	while (!list_empty(&fs_info->reclaim_bgs)) {
 		bg = list_first_entry(&fs_info->reclaim_bgs,