Merge tag 'kvm-s390-next-5.7-1' of git://git.kernel.org/pub/scm/linux/kernel/git/kvms390/linux into HEAD

KVM: s390: Features and Enhancements for 5.7 part1

1. Allow to disable gisa
2. protected virtual machines
  Protected VMs (PVM) are KVM VMs, where KVM can't access the VM's
  state like guest memory and guest registers anymore. Instead the
  PVMs are mostly managed by a new entity called Ultravisor (UV),
  which provides an API, so KVM and the PV can request management
  actions.

  PVMs are encrypted at rest and protected from hypervisor access
  while running.  They switch from a normal operation into protected
  mode, so we can still use the standard boot process to load a
  encrypted blob and then move it into protected mode.

  Rebooting is only possible by passing through the unprotected/normal
  mode and switching to protected again.

  One mm related patch will go via Andrews mm tree ( mm/gup/writeback:
  add callbacks for inaccessible pages)

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)