From: Joshua Hahn <joshua.hahnjy@gmail.com>
Date: Mon, 2 Jun 2025 16:23:40 +0000 (-0700)
Subject: mm/mempolicy: skip unnecessary synchronize_rcu()
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=1ec8a6e30e9c4ad06ea5e94536623c59c4ae2400;p=thirdparty%2Fkernel%2Flinux.git

mm/mempolicy: skip unnecessary synchronize_rcu()

By unconditionally setting wi_state to NULL and conditionally calling
synchronize_rcu(), we can save an unncessary call when there is no
old_wi_state.

Link: https://lkml.kernel.org/r/20250602162345.2595696-2-joshua.hahnjy@gmail.com
Signed-off-by: Joshua Hahn <joshua.hahnjy@gmail.com>
Suggested-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Huang Ying <ying.huang@linux.alibaba.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Byungchul Park <byungchul@sk.com>
Cc: Gregory Price <gourry@gourry.net>
Cc: "Huang, Ying" <ying.huang@linux.alibaba.com>
Cc: kernel test robot <lkp@intel.com>
Cc: Mathew Brost <matthew.brost@intel.com>
Cc: Rakie Kim <rakie.kim@sk.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 3b1dfd08338bd..b0619d0020c93 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -3703,18 +3703,15 @@ static void wi_state_free(void)
 	struct weighted_interleave_state *old_wi_state;
 
 	mutex_lock(&wi_state_lock);
-
 	old_wi_state = rcu_dereference_protected(wi_state,
 			lockdep_is_held(&wi_state_lock));
-	if (!old_wi_state) {
-		mutex_unlock(&wi_state_lock);
-		return;
-	}
-
 	rcu_assign_pointer(wi_state, NULL);
 	mutex_unlock(&wi_state_lock);
-	synchronize_rcu();
-	kfree(old_wi_state);
+
+	if (old_wi_state) {
+		synchronize_rcu();
+		kfree(old_wi_state);
+	}
 }
 
 static struct kobj_attribute wi_auto_attr =