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=-3.5 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS autolearn=no 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 AFF18C76191 for ; Thu, 18 Jul 2019 13:53:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C8A2321019 for ; Thu, 18 Jul 2019 13:53:34 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="YSUYAiWq" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390529AbfGRNxd (ORCPT ); Thu, 18 Jul 2019 09:53:33 -0400 Received: from merlin.infradead.org ([205.233.59.134]:43900 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727791AbfGRNxd (ORCPT ); Thu, 18 Jul 2019 09:53:33 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=Content-Type:MIME-Version:References: Subject:Cc:To:From:Date:Message-Id:Sender:Reply-To:Content-Transfer-Encoding: Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender: Resent-To:Resent-Cc:Resent-Message-ID:In-Reply-To:List-Id:List-Help: List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=KL6fWBl+CLFFt4aWnjiO8B6w4bZAMG4MS2WQ/d3Yocs=; b=YSUYAiWqzr3DBTxBUoIHCVB9rg 1l5UxWSMkH1h/NyNXxkVxOEBP13QgeXflotf//fBzpymWqjRzKYlyQbtYAJ0sEdenTljMTXBJoU5J dHQCFwtw+wAF3z9vBSYbpFdewzL/hcKwjrVHp/6aOhWxR0HSje30mnK7GqY0shlu2FuxJkVHeBznA Cuh244+8gWxUaDV2pmiwLQcIytasglWvs5AuqkiP8t847bXeXybls5t9tABs1OBcimU1Bjss70oGe OInyY2DJp2+rSAvvulh4fdxCDjMvMd/Mt2BsYmETi589WR2s2Vw0obDkk2Gi3LhTVQ0ScRDtOOux5 Dlr/4nVQ==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92 #3 (Red Hat Linux)) id 1ho6qb-0003u4-GB; Thu, 18 Jul 2019 13:53:25 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 0) id C768320B979A4; Thu, 18 Jul 2019 15:53:22 +0200 (CEST) Message-Id: <20190718135206.012378477@infradead.org> User-Agent: quilt/0.65 Date: Thu, 18 Jul 2019 15:49:56 +0200 From: Peter Zijlstra To: Will Deacon Cc: linux-kernel@vger.kernel.org, Peter Zijlstra , Jan Stancek , Waiman Long , dbueso@suse.de, mingo@redhat.com, jade.alglave@arm.com, paulmck@linux.vnet.ibm.com Subject: [PATCH 2/4] rwsem: Add missing ACQUIRE to read_slowpath sleep loop References: <20190718134954.496297975@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org While reviewing another read_slowpath patch, both Will and I noticed another missing ACQUIRE, namely: X = 0; CPU0 CPU1 rwsem_down_read() for (;;) { set_current_state(TASK_UNINTERRUPTIBLE); X = 1; rwsem_up_write(); rwsem_mark_wake() atomic_long_add(adjustment, &sem->count); smp_store_release(&waiter->task, NULL); if (!waiter.task) break; ... } r = X; Allows 'r == 0'. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Reported-by: Peter Zijlstra (Intel) Reported-by: Will Deacon Acked-by: Will Deacon Signed-off-by: Peter Zijlstra (Intel) --- kernel/locking/rwsem.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) --- a/kernel/locking/rwsem.c +++ b/kernel/locking/rwsem.c @@ -1069,8 +1069,10 @@ rwsem_down_read_slowpath(struct rw_semap /* wait to be given the lock */ while (true) { set_current_state(state); - if (!waiter.task) + if (!smp_load_acquire(&waiter.task)) { + /* Orders against rwsem_mark_wake()'s smp_store_release() */ break; + } if (signal_pending_state(state, current)) { raw_spin_lock_irq(&sem->wait_lock); if (waiter.task)