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Btrfs: use down_read_nested to make lockdep silent 

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>
This commit is contained in:
Liu Bo 2016-11-30 16:11:04 -08:00 committed by David Sterba
parent d028099643
commit e321f8a801
1 changed files with 2 additions and 1 deletions
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3
fs/btrfs/extent-tree.c
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@ -7387,7 +7387,8 @@ 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)