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=-9.0 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT 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 4A5D8C43387 for ; Thu, 20 Dec 2018 09:26:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 19D13218D8 for ; Thu, 20 Dec 2018 09:26:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1545298006; bh=Dp781QzXBoae/xoPg/n69YM5KGJBNViX5dW6DJA8xSc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=mxwJ2goL7jqrxjvyM3j/OBbVTQ86MYkO8cIZ3ES1AAkRZpCpoqyE4Ucq/9NwVUkab BLmWWEx23PheqLEnFUkU2ardsMmaSho1Gz53I4zFX6Xd9kDeMy/FTg4ypxYXygJFYl jPnKfDxpyRdKcRdDySBV9dpFqQU/U/8UAgzNMDpA= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732156AbeLTJ0o (ORCPT ); Thu, 20 Dec 2018 04:26:44 -0500 Received: from mail.kernel.org ([198.145.29.99]:57418 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732140AbeLTJ0m (ORCPT ); Thu, 20 Dec 2018 04:26:42 -0500 Received: from localhost (5356596B.cm-6-7b.dynamic.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id EFB9620656; Thu, 20 Dec 2018 09:26:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1545298001; bh=Dp781QzXBoae/xoPg/n69YM5KGJBNViX5dW6DJA8xSc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=b043WTT3XyBLKx3Q1+FRYpJ9UkdIKUgEO+ZH5HXWEU60vX3d+FMW4xmnUQReO7kIt aDfc2YPlc+9Y2y2/9fhs5DSvuEWsZAs3zYl2cSfHQtoOhOlG1uItIkw0m2eggaW5mY sUvbQ3c6R6QIJV/46I7pwXbd2dZj6Rtikov0UlW0= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, "Peter Zijlstra (Intel)" , Will Deacon , Linus Torvalds , Thomas Gleixner , andrea.parri@amarulasolutions.com, longman@redhat.com, Ingo Molnar , Sebastian Andrzej Siewior , Sasha Levin Subject: [PATCH 4.14 27/72] locking/qspinlock: Re-order code Date: Thu, 20 Dec 2018 10:18:26 +0100 Message-Id: <20181220085923.406505183@linuxfoundation.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20181220085922.332225035@linuxfoundation.org> References: <20181220085922.332225035@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review X-Patchwork-Hint: ignore MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 4.14-stable review patch. If anyone has any objections, please let me know. ------------------ commit 53bf57fab7321fb42b703056a4c80fc9d986d170 upstream. Flip the branch condition after atomic_fetch_or_acquire(_Q_PENDING_VAL) such that we loose the indent. This also result in a more natural code flow IMO. Signed-off-by: Peter Zijlstra (Intel) Acked-by: Will Deacon Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: andrea.parri@amarulasolutions.com Cc: longman@redhat.com Link: https://lkml.kernel.org/r/20181003130257.156322446@infradead.org Signed-off-by: Ingo Molnar Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Sasha Levin --- kernel/locking/qspinlock.c | 54 ++++++++++++++++++-------------------- 1 file changed, 26 insertions(+), 28 deletions(-) diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c index 841550dfb7b8..9ffc2f9af8b8 100644 --- a/kernel/locking/qspinlock.c +++ b/kernel/locking/qspinlock.c @@ -324,38 +324,36 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val) * 0,0,1 -> 0,1,1 ; pending */ val = atomic_fetch_or_acquire(_Q_PENDING_VAL, &lock->val); - if (!(val & ~_Q_LOCKED_MASK)) { - /* - * We're pending, wait for the owner to go away. - * - * *,1,1 -> *,1,0 - * - * this wait loop must be a load-acquire such that we match the - * store-release that clears the locked bit and create lock - * sequentiality; this is because not all - * clear_pending_set_locked() implementations imply full - * barriers. - */ - if (val & _Q_LOCKED_MASK) { - smp_cond_load_acquire(&lock->val.counter, - !(VAL & _Q_LOCKED_MASK)); - } - - /* - * take ownership and clear the pending bit. - * - * *,1,0 -> *,0,1 - */ - clear_pending_set_locked(lock); - return; + /* + * If we observe any contention; undo and queue. + */ + if (unlikely(val & ~_Q_LOCKED_MASK)) { + if (!(val & _Q_PENDING_MASK)) + clear_pending(lock); + goto queue; } /* - * If pending was clear but there are waiters in the queue, then - * we need to undo our setting of pending before we queue ourselves. + * We're pending, wait for the owner to go away. + * + * 0,1,1 -> 0,1,0 + * + * this wait loop must be a load-acquire such that we match the + * store-release that clears the locked bit and create lock + * sequentiality; this is because not all + * clear_pending_set_locked() implementations imply full + * barriers. + */ + if (val & _Q_LOCKED_MASK) + smp_cond_load_acquire(&lock->val.counter, !(VAL & _Q_LOCKED_MASK)); + + /* + * take ownership and clear the pending bit. + * + * 0,1,0 -> 0,0,1 */ - if (!(val & _Q_PENDING_MASK)) - clear_pending(lock); + clear_pending_set_locked(lock); + return; /* * End of pending bit optimistic spinning and beginning of MCS -- 2.19.1