1 files changed, 23 insertions, 2 deletions

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 25dcff71e451..41a5688ffdfe 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -7430,7 +7430,26 @@ static int lock_extent_direct(struct inode *inode, u64 lockstart, u64 lockend,
                                      cached_state, GFP_NOFS);
 
                 if (ordered) {
-                        btrfs_start_ordered_extent(inode, ordered, 1);
+                        /*
+                         * If we are doing a DIO read and the ordered extent we
+                         * found is for a buffered write, we can not wait for it
+                         * to complete and retry, because if we do so we can
+                         * deadlock with concurrent buffered writes on page
+                         * locks. This happens only if our DIO read covers more
+                         * than one extent map, if at this point has already
+                         * created an ordered extent for a previous extent map
+                         * and locked its range in the inode's io tree, and a
+                         * concurrent write against that previous extent map's
+                         * range and this range started (we unlock the ranges
+                         * in the io tree only when the bios complete and
+                         * buffered writes always lock pages before attempting
+                         * to lock range in the io tree).
+                         */
+                        if (writing ||
+                            test_bit(BTRFS_ORDERED_DIRECT, &ordered->flags))
+                                btrfs_start_ordered_extent(inode, ordered, 1);
+                        else
+                                ret = -ENOTBLK;
                         btrfs_put_ordered_extent(ordered);
                 } else {
                         /*
@@ -7447,9 +7466,11 @@ static int lock_extent_direct(struct inode *inode, u64 lockstart, u64 lockend,
                          * that page.
                          */
                         ret = -ENOTBLK;
-                        break;
                 }
 
+                if (ret)
+                        break;
+
                 cond_resched();
         }