linux-kernel - [PATCH] security, keys: Optimize barrier usage for Rmw atomic bitops

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Date:   Wed, 29 Jan 2020 10:06:25 -0800
From:   Davidlohr Bueso <dave@...olabs.net>
To:     dhowells@...hat.com
Cc:     linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, dave@...olabs.net,
        Davidlohr Bueso <dbueso@...e.de>
Subject: [PATCH] security, keys: Optimize barrier usage for Rmw atomic  bitops

For both set and clear_bit, we can avoid the unnecessary barriers
on non LL/SC architectures, such as x86. Instead, use the
smp_mb__{before,after}_atomic() calls.

Signed-off-by: Davidlohr Bueso <dbueso@...e.de>
---
 security/keys/gc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/security/keys/gc.c b/security/keys/gc.c
index 671dd730ecfc..ce7b4c22e3c4 100644
--- a/security/keys/gc.c
+++ b/security/keys/gc.c
@@ -102,7 +102,7 @@ void key_gc_keytype(struct key_type *ktype)
 
 	key_gc_dead_keytype = ktype;
 	set_bit(KEY_GC_REAPING_KEYTYPE, &key_gc_flags);
-	smp_mb();
+	smp_mb__after_atomic();
 	set_bit(KEY_GC_REAP_KEYTYPE, &key_gc_flags);
 
 	kdebug("schedule");
@@ -308,7 +308,7 @@ static void key_garbage_collector(struct work_struct *work)
 
 	if (unlikely(gc_state & KEY_GC_REAPING_DEAD_3)) {
 		kdebug("dead wake");
-		smp_mb();
+		smp_mb__before_atomic();
 		clear_bit(KEY_GC_REAPING_KEYTYPE, &key_gc_flags);
 		wake_up_bit(&key_gc_flags, KEY_GC_REAPING_KEYTYPE);
 	}
-- 
2.16.4