Merge tag 'for-5.6-rc1-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux

Pull btrfs fixes from David Sterba:
 "Two races fixed, memory leak fix, sysfs directory fixup and two new
  log messages:

   - two fixed race conditions: extent map merging and truncate vs
     fiemap

   - create the right sysfs directory with device information and move
     the individual device dirs under it

   - print messages when the tree-log is replayed at mount time or
     cannot be replayed on remount"

* tag 'for-5.6-rc1-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux:
  btrfs: sysfs, move device id directories to UUID/devinfo
  btrfs: sysfs, add UUID/devinfo kobject
  Btrfs: fix race between shrinking truncate and fiemap
  btrfs: log message when rw remount is attempted with unclean tree-log
  btrfs: print message when tree-log replay starts
  Btrfs: fix race between using extent maps and merging them
  btrfs: ref-verify: fix memory leaks

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)