linux-kernel - [PATCH 5.16 0886/1039] btrfs: zoned: unset dedicated block group on allocation failure

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Date:   Mon, 24 Jan 2022 19:44:35 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Naohiro Aota <naohiro.aota@....com>,
        David Sterba <dsterba@...e.com>
Subject: [PATCH 5.16 0886/1039] btrfs: zoned: unset dedicated block group on allocation failure

From: Naohiro Aota <naohiro.aota@....com>

commit 1ada69f61c88abb75a1038ee457633325658a183 upstream.

Allocating an extent from a block group can fail for various reasons.
When an allocation from a dedicated block group (for tree-log or
relocation data) fails, we need to unregister it as a dedicated one so
that we can allocate a new block group for the dedicated one.

However, we are returning early when the block group in case it is
read-only, fully used, or not be able to activate the zone. As a result,
we keep the non-usable block group as a dedicated one, leading to
further allocation failure. With many block groups, the allocator will
iterate hopeless loop to find a free extent, results in a hung task.

Fix the issue by delaying the return and doing the proper cleanups.

CC: stable@...r.kernel.org # 5.16
Signed-off-by: Naohiro Aota <naohiro.aota@....com>
Signed-off-by: David Sterba <dsterba@...e.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 fs/btrfs/extent-tree.c |   20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -3790,23 +3790,35 @@ static int do_allocation_zoned(struct bt
 	spin_unlock(&fs_info->relocation_bg_lock);
 	if (skip)
 		return 1;
+
 	/* Check RO and no space case before trying to activate it */
 	spin_lock(&block_group->lock);
 	if (block_group->ro ||
 	    block_group->alloc_offset == block_group->zone_capacity) {
-		spin_unlock(&block_group->lock);
-		return 1;
+		ret = 1;
+		/*
+		 * May need to clear fs_info->{treelog,data_reloc}_bg.
+		 * Return the error after taking the locks.
+		 */
 	}
 	spin_unlock(&block_group->lock);
 
-	if (!btrfs_zone_activate(block_group))
-		return 1;
+	if (!ret && !btrfs_zone_activate(block_group)) {
+		ret = 1;
+		/*
+		 * May need to clear fs_info->{treelog,data_reloc}_bg.
+		 * Return the error after taking the locks.
+		 */
+	}
 
 	spin_lock(&space_info->lock);
 	spin_lock(&block_group->lock);
 	spin_lock(&fs_info->treelog_bg_lock);
 	spin_lock(&fs_info->relocation_bg_lock);
 
+	if (ret)
+		goto out;
+
 	ASSERT(!ffe_ctl->for_treelog ||
 	       block_group->start == fs_info->treelog_bg ||
 	       fs_info->treelog_bg == 0);