Btrfs: Fix bookend extent race v2

When dropping middle part of an extent, btrfs_drop_extents truncates
the extent at first, then inserts a bookend extent.

Since truncation and insertion can't be done atomically, there is a small
period that the bookend extent isn't in the tree. This causes problem for
functions that search the tree for file extent item. The way to fix this is
lock the range of the bookend extent before truncation.

Signed-off-by: Yan Zheng <zheng.yan@oracle.com>

1 files changed, 5 insertions, 1 deletions

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 7503bd46819b..65a0583027e9 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -946,8 +946,12 @@ int try_lock_extent(struct extent_io_tree *tree, u64 start, u64 end,
 
         err = set_extent_bit(tree, start, end, EXTENT_LOCKED, 1,
                              &failed_start, mask);
-        if (err == -EEXIST)
+        if (err == -EEXIST) {
+                if (failed_start > start)
+                        clear_extent_bit(tree, start, failed_start - 1,
+                                         EXTENT_LOCKED, 1, 0, mask);
                 return 0;
+        }
         return 1;
 }
 EXPORT_SYMBOL(try_lock_extent);