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-rw-r--r--fs/btrfs/extent_map.c11
1 files changed, 11 insertions, 0 deletions
diff --git a/fs/btrfs/extent_map.c b/fs/btrfs/extent_map.c
index 6f417ff68980..bd6229fb2b6f 100644
--- a/fs/btrfs/extent_map.c
+++ b/fs/btrfs/extent_map.c
@@ -237,6 +237,17 @@ static void try_merge_map(struct extent_map_tree *tree, struct extent_map *em)
struct extent_map *merge = NULL;
struct rb_node *rb;
+ /*
+ * We can't modify an extent map that is in the tree and that is being
+ * used by another task, as it can cause that other task to see it in
+ * inconsistent state during the merging. We always have 1 reference for
+ * the tree and 1 for this task (which is unpinning the extent map or
+ * clearing the logging flag), so anything > 2 means it's being used by
+ * other tasks too.
+ */
+ if (refcount_read(&em->refs) > 2)
+ return;
+
if (em->start != 0) {
rb = rb_prev(&em->rb_node);
if (rb)