From: Jeff Layton <jlayton@kernel.org>
Date: Tue, 1 Jun 2021 09:24:38 -0400
Subject: ceph: clean up locking annotation for ceph_get_snap_realm and
 __lookup_snap_realm
Git-commit: df2c0cb7f8e8c83e495260ad86df8c5da947f2a7
Patch-mainline: v5.14-rc1
References: bsc#1201149

They both say that the snap_rwsem must be held for write, but I don't
see any real reason for it, and it's not currently always called that
way.

The lookup is just walking the rbtree, so holding it for read should be
fine there. The "get" is bumping the refcount and (possibly) removing
it from the empty list. I see no need to hold the snap_rwsem for write
for that.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Acked-by: Luis Henriques <lhenriques@suse.com>

---
 fs/ceph/snap.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/fs/ceph/snap.c b/fs/ceph/snap.c
index bc6c33d485e6..f8cac2abab3f 100644
--- a/fs/ceph/snap.c
+++ b/fs/ceph/snap.c
@@ -60,12 +60,12 @@
 /*
  * increase ref count for the realm
  *
- * caller must hold snap_rwsem for write.
+ * caller must hold snap_rwsem.
  */
 void ceph_get_snap_realm(struct ceph_mds_client *mdsc,
 			 struct ceph_snap_realm *realm)
 {
-	lockdep_assert_held_write(&mdsc->snap_rwsem);
+	lockdep_assert_held(&mdsc->snap_rwsem);
 
 	dout("get_realm %p %d -> %d\n", realm,
 	     atomic_read(&realm->nref), atomic_read(&realm->nref)+1);
@@ -139,7 +139,7 @@ static struct ceph_snap_realm *ceph_create_snap_realm(
 /*
  * lookup the realm rooted at @ino.
  *
- * caller must hold snap_rwsem for write.
+ * caller must hold snap_rwsem.
  */
 static struct ceph_snap_realm *__lookup_snap_realm(struct ceph_mds_client *mdsc,
 						   u64 ino)
@@ -147,7 +147,7 @@ static struct ceph_snap_realm *__lookup_snap_realm(struct ceph_mds_client *mdsc,
 	struct rb_node *n = mdsc->snap_realms.rb_node;
 	struct ceph_snap_realm *r;
 
-	lockdep_assert_held_write(&mdsc->snap_rwsem);
+	lockdep_assert_held(&mdsc->snap_rwsem);
 
 	while (n) {
 		r = rb_entry(n, struct ceph_snap_realm, node);