From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 58137C11F65 for ; Wed, 30 Jun 2021 15:42:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4107C61493 for ; Wed, 30 Jun 2021 15:42:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235919AbhF3PpG (ORCPT ); Wed, 30 Jun 2021 11:45:06 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43186 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235828AbhF3PpF (ORCPT ); Wed, 30 Jun 2021 11:45:05 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 73CA2C061756 for ; Wed, 30 Jun 2021 08:42:36 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=Content-Type:MIME-Version:References: Subject:Cc:To:From:Date:Message-ID:Sender:Reply-To:Content-Transfer-Encoding: Content-ID:Content-Description:In-Reply-To; bh=2hdvY05lg7IflWRpLH9FzHf5vvhAFMGhIYa0tWNvg7g=; b=KWNzHn2/tsqup0QHYcOrnwl4Lg wNWgle6r4VMVzt2EMv43rnIs6CLXdjqXfxoFIiQtIXiOKQV587gPk/rbUzvOuWsT52tNHFuXg0lZr HmMh/02OTmw44wTGpoErMckaktDriFn6RhNgC+JMWn7r067zJCKVAn0gsTewIJylj1Cm+DW126wBN GzZgVZLC13HiXyS3QYWCcL5ZllJBD69EYVRMIQYNo0Qnd1YBxcy6bhohWnAQet2Kj34ME2GqYDOeK 6UebwAt2h9JU/VZvUgLcGGcEdAoc9ysu/GRcmBk70B7khuX23wGOOybJ/3pg5vap98i32Z6WCnXCO Qb9GyuXQ==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1lycLo-005Vpa-Fy; Wed, 30 Jun 2021 15:42:13 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 490973002D3; Wed, 30 Jun 2021 17:42:06 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 0) id 2EECD2C59D76E; Wed, 30 Jun 2021 17:42:06 +0200 (CEST) Message-ID: <20210630154114.834438545@infradead.org> User-Agent: quilt/0.66 Date: Wed, 30 Jun 2021 17:35:17 +0200 From: Peter Zijlstra To: mingo@redhat.com, longman@redhat.com, boqun.feng@gmail.com, will@kernel.org Cc: linux-kernel@vger.kernel.org, peterz@infradead.org, yanfei.xu@windriver.com Subject: [RFC][PATCH 1/4] locking/mutex: Use try_cmpxchg() References: <20210630153516.832731403@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org For simpler and better code. Signed-off-by: Peter Zijlstra (Intel) --- kernel/locking/mutex.c | 27 ++++++--------------------- 1 file changed, 6 insertions(+), 21 deletions(-) --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -100,7 +100,7 @@ static inline struct task_struct *__mute owner = atomic_long_read(&lock->owner); for (;;) { /* must loop, can race against a flag */ - unsigned long old, flags = __owner_flags(owner); + unsigned long flags = __owner_flags(owner); unsigned long task = owner & ~MUTEX_FLAGS; if (task) { @@ -124,11 +124,8 @@ static inline struct task_struct *__mute */ flags &= ~MUTEX_FLAG_HANDOFF; - old = atomic_long_cmpxchg_acquire(&lock->owner, owner, curr | flags); - if (old == owner) + if (atomic_long_try_cmpxchg_acquire(&lock->owner, &owner, curr | flags)) return NULL; - - owner = old; } return __owner_task(owner); @@ -168,10 +165,7 @@ static __always_inline bool __mutex_unlo { unsigned long curr = (unsigned long)current; - if (atomic_long_cmpxchg_release(&lock->owner, curr, 0UL) == curr) - return true; - - return false; + return atomic_long_try_cmpxchg_release(&lock->owner, &curr, 0UL); } #endif @@ -226,7 +220,7 @@ static void __mutex_handoff(struct mutex unsigned long owner = atomic_long_read(&lock->owner); for (;;) { - unsigned long old, new; + unsigned long new; #ifdef CONFIG_DEBUG_MUTEXES DEBUG_LOCKS_WARN_ON(__owner_task(owner) != current); @@ -238,11 +232,8 @@ static void __mutex_handoff(struct mutex if (task) new |= MUTEX_FLAG_PICKUP; - old = atomic_long_cmpxchg_release(&lock->owner, owner, new); - if (old == owner) + if (atomic_long_try_cmpxchg_release(&lock->owner, &owner, new)) break; - - owner = old; } } @@ -1237,8 +1228,6 @@ static noinline void __sched __mutex_unl */ owner = atomic_long_read(&lock->owner); for (;;) { - unsigned long old; - #ifdef CONFIG_DEBUG_MUTEXES DEBUG_LOCKS_WARN_ON(__owner_task(owner) != current); DEBUG_LOCKS_WARN_ON(owner & MUTEX_FLAG_PICKUP); @@ -1247,16 +1236,12 @@ static noinline void __sched __mutex_unl if (owner & MUTEX_FLAG_HANDOFF) break; - old = atomic_long_cmpxchg_release(&lock->owner, owner, - __owner_flags(owner)); - if (old == owner) { + if (atomic_long_try_cmpxchg_release(&lock->owner, &owner, __owner_flags(owner))) { if (owner & MUTEX_FLAG_WAITERS) break; return; } - - owner = old; } spin_lock(&lock->wait_lock);