[PATCH for v4.9 LTS 34/87] Btrfs: use down_read_nested to make lockdep silent

From	"Levin, Alexander (Sasha Levin)" <alexander.levin@verizon.com>
Newsgroups	linux.kernel
Subject	[PATCH for v4.9 LTS 34/87] Btrfs: use down_read_nested to make lockdep silent
Date	2017-07-15 03:50 +0200
Message-ID	<u3knw-3kv-21@gated-at.bofh.it> (permalink)
References	<u3k49-3a5-3@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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From: Liu Bo <bo.li.liu@oracle.com>

[ Upstream commit e321f8a801d7b4c40da8005257b05b9c2b51b072 ]

If @block_group is not @used_bg, it'll try to get @used_bg's lock without
droping @block_group 's lock and lockdep has throwed a scary deadlock warning
about it.
Fix it by using down_read_nested.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
---
 fs/btrfs/extent-tree.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index e46e7fbe1b34..14a37ff0b9e3 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -7401,7 +7401,8 @@ btrfs_lock_cluster(struct btrfs_block_group_cache *block_group,
 
 		spin_unlock(&cluster->refill_lock);
 
-		down_read(&used_bg->data_rwsem);
+		/* We should only have one-level nested. */
+		down_read_nested(&used_bg->data_rwsem, SINGLE_DEPTH_NESTING);
 
 		spin_lock(&cluster->refill_lock);
 		if (used_bg == cluster->block_group)
-- 
2.11.0

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[PATCH for v4.9 LTS 34/87] Btrfs: use down_read_nested to make  lockdep silent "Levin, Alexander (Sasha Levin)" <alexander.levin@verizon.com> - 2017-07-15 03:50 +0200

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