Btrfs: use the commit_root for reading free_space_inode crcs

Now that we are using regular file crcs for the free space cache,
we can deadlock if we try to read the free_space_inode while we are
updating the crc tree.

This commit fixes things by using the commit_root to read the crcs.  This is
safe because we the free space cache file would already be loaded if
that block group had been changed in the current transaction.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/fs/btrfs/file-item.c b/fs/btrfs/file-item.c
index bb22a44..08bcfa9 100644
--- a/fs/btrfs/file-item.c
+++ b/fs/btrfs/file-item.c
@@ -177,6 +177,15 @@ static int __btrfs_lookup_bio_sums(struct btrfs_root *root,
 
 	WARN_ON(bio->bi_vcnt <= 0);
 
+	/*
+	 * the free space stuff is only read when it hasn't been
+	 * updated in the current transaction.  So, we can safely
+	 * read from the commit root and sidestep a nasty deadlock
+	 * between reading the free space cache and updating the csum tree.
+	 */
+	if (btrfs_is_free_space_inode(root, inode))
+		path->search_commit_root = 1;
+
 	disk_bytenr = (u64)bio->bi_sector << 9;
 	if (dio)
 		offset = logical_offset;