linux-kernel - [PATCH AUTOSEL 4.19 161/258] btrfs: reada: reorder dev-replace locks before radix tree preload

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Date:   Mon, 28 Jan 2019 10:57:47 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     David Sterba <dsterba@...e.com>, Sasha Levin <sashal@...nel.org>,
        linux-btrfs@...r.kernel.org
Subject: [PATCH AUTOSEL 4.19 161/258] btrfs: reada: reorder dev-replace locks before radix tree preload

From: David Sterba <dsterba@...e.com>

[ 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@...e.com>
Signed-off-by: Sasha Levin <sashal@...nel.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