We're holding the sb_start_intwrite lock at this point, and doing async
filemap_flush of the inodes will result in a deadlock if we freeze the
fs during this operation. This is because we could do a
btrfs_join_transaction() in the thread we are waiting on which would
block at sb_start_intwrite, and thus deadlock. Using
writeback_inodes_sb() side steps the problem by not introducing all of
these extra locking dependencies.
Signed-off-by: Josef Bacik <jbacik@xxxxxx>
---
fs/btrfs/transaction.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 68c3e1c04bca..5a8c2649af2f 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -1916,8 +1916,17 @@ static void cleanup_transaction(struct btrfs_trans_handle *trans,
static inline int btrfs_start_delalloc_flush(struct btrfs_fs_info *fs_info)
{
+ /*
+ * We use writeback_inodes_sb here because if we used
+ * btrfs_start_delalloc_roots we would deadlock with fs freeze.
+ * Currently are holding the fs freeze lock, if we do an async flush
+ * we'll do btrfs_join_transaction() and deadlock because we need to
+ * wait for the fs freeze lock. Using the direct flushing we benefit
+ * from already being in a transaction and our join_transaction doesn't
+ * have to re-take the fs freeze lock.
+ */
if (btrfs_test_opt(fs_info, FLUSHONCOMMIT))
- return btrfs_start_delalloc_roots(fs_info, 1, -1);
+ writeback_inodes_sb(fs_info->sb, WB_REASON_SYNC);
return 0;
}
--
2.7.5
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