Btrfs: avoid deadlocks during reservations in btrfs_truncate_block

The new enospc code makes it possible to deadlock if we don't use
FLUSH_LIMIT during reservations inside a transaction.  This enforces
the correct flush type to avoid both deadlocks and assertions

Signed-off-by: Chris Mason <clm@fb.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 3a129c42658e..9fcb8c97083b 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -5939,10 +5939,15 @@ int btrfs_delalloc_reserve_metadata(struct inode *inode, u64 num_bytes)
          * the middle of a transaction commit.  We also don't need the delalloc
          * mutex since we won't race with anybody.  We need this mostly to make
          * lockdep shut its filthy mouth.
+         *
+         * If we have a transaction open (can happen if we call truncate_block
+         * from truncate), then we need FLUSH_LIMIT so we don't deadlock.
          */
         if (btrfs_is_free_space_inode(inode)) {
                 flush = BTRFS_RESERVE_NO_FLUSH;
                 delalloc_lock = false;
+        } else if (current->journal_info) {
+                flush = BTRFS_RESERVE_FLUSH_LIMIT;
         }
 
         if (flush != BTRFS_RESERVE_NO_FLUSH &&