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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, David Sterba <dsterba@suse.com>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 4.20 181/352] btrfs: reada: reorder dev-replace locks before radix tree preload
Date:   Mon, 11 Feb 2019 15:16:48 +0100
Message-Id: <20190211141858.608391723@linuxfoundation.org>
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4.20-stable review patch.  If anyone has any objections, please let me know.

------------------

[ Upstream commit ceb21a8db48559fd0809e03c4df9eb37743d9170 ]

The device-replace read lock is going to use rw semaphore in followup
commits. The semaphore might sleep which is not possible in the radix
tree preload section. The lock nesting is now:

* device replace
  * radix tree preload
    * readahead spinlock

Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/btrfs/reada.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/fs/btrfs/reada.c b/fs/btrfs/reada.c
index dec14b739b10..6f81f3e88b6d 100644
--- a/fs/btrfs/reada.c
+++ b/fs/btrfs/reada.c
@@ -376,26 +376,28 @@ static struct reada_extent *reada_find_extent(struct btrfs_fs_info *fs_info,
 		goto error;
 	}
 
+	/* Insert extent in reada tree + all per-device trees, all or nothing */
+	btrfs_dev_replace_read_lock(&fs_info->dev_replace);
 	ret = radix_tree_preload(GFP_KERNEL);
-	if (ret)
+	if (ret) {
+		btrfs_dev_replace_read_unlock(&fs_info->dev_replace);
 		goto error;
+	}
 
-	/* insert extent in reada_tree + all per-device trees, all or nothing */
-	btrfs_dev_replace_read_lock(&fs_info->dev_replace);
 	spin_lock(&fs_info->reada_lock);
 	ret = radix_tree_insert(&fs_info->reada_tree, index, re);
 	if (ret == -EEXIST) {
 		re_exist = radix_tree_lookup(&fs_info->reada_tree, index);
 		re_exist->refcnt++;
 		spin_unlock(&fs_info->reada_lock);
-		btrfs_dev_replace_read_unlock(&fs_info->dev_replace);
 		radix_tree_preload_end();
+		btrfs_dev_replace_read_unlock(&fs_info->dev_replace);
 		goto error;
 	}
 	if (ret) {
 		spin_unlock(&fs_info->reada_lock);
-		btrfs_dev_replace_read_unlock(&fs_info->dev_replace);
 		radix_tree_preload_end();
+		btrfs_dev_replace_read_unlock(&fs_info->dev_replace);
 		goto error;
 	}
 	radix_tree_preload_end();
-- 
2.19.1