dm: use rcu_dereference_protected instead of rcu_dereference

rcu_dereference() should be used in sections protected by rcu_read_lock.

For writers, holding some kind of mutex or lock,
rcu_dereference_protected() is the way to go, adding explicit lockdep
bits.

In __unbind(), we are the last user of this mapped device, so can use
the constant '1' instead of a lockdep_is_held(), not consistent with
other uses of rcu_dereference_protected() which use md->suspend_lock
mutex.

Reported-by: Kirill A. Shutemov <kirill@shutemov.name>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Fixes: 33423974bfc1 ("dm: Use rcu_dereference() for accessing rcu pointer")
Cc: Pranith Kumar <bobby.prani@gmail.com>
[snitzer: allow lines longer than 80 columns, refine subject]
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm.c

@@ -2335,7 +2335,7 @@ static struct dm_table *__bind(struct mapped_device *md, struct dm_table *t,
 
 	merge_is_optional = dm_table_merge_is_optional(t);
 
-	old_map = rcu_dereference(md->map);
+	old_map = rcu_dereference_protected(md->map, lockdep_is_held(&md->suspend_lock));
 	rcu_assign_pointer(md->map, t);
 	md->immutable_target_type = dm_table_get_immutable_target_type(t);
 
@@ -2355,7 +2355,7 @@ static struct dm_table *__bind(struct mapped_device *md, struct dm_table *t,
  */
 static struct dm_table *__unbind(struct mapped_device *md)
 {
-	struct dm_table *map = rcu_dereference(md->map);
+	struct dm_table *map = rcu_dereference_protected(md->map, 1);
 
 	if (!map)
 		return NULL;
@@ -2850,7 +2850,7 @@ retry:
 		goto retry;
 	}
 
-	map = rcu_dereference(md->map);
+	map = rcu_dereference_protected(md->map, lockdep_is_held(&md->suspend_lock));
 
 	r = __dm_suspend(md, map, suspend_flags, TASK_INTERRUPTIBLE);
 	if (r)
@@ -2908,7 +2908,7 @@ retry:
 		goto retry;
 	}
 
-	map = rcu_dereference(md->map);
+	map = rcu_dereference_protected(md->map, lockdep_is_held(&md->suspend_lock));
 	if (!map || !dm_table_get_size(map))
 		goto out;
 
@@ -2943,7 +2943,7 @@ static void __dm_internal_suspend(struct mapped_device *md, unsigned suspend_fla
 		return; /* nest suspend */
 	}
 
-	map = rcu_dereference(md->map);
+	map = rcu_dereference_protected(md->map, lockdep_is_held(&md->suspend_lock));
 
 	/*
 	 * Using TASK_UNINTERRUPTIBLE because only NOFLUSH internal suspend is