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,URIBL_BLOCKED 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 F2E81C76195 for ; Thu, 18 Jul 2019 13:53:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CAE102173E for ; Thu, 18 Jul 2019 13:53:38 +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="yGZ9f+yo" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390604AbfGRNxi (ORCPT ); Thu, 18 Jul 2019 09:53:38 -0400 Received: from merlin.infradead.org ([205.233.59.134]:43912 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390573AbfGRNxh (ORCPT ); Thu, 18 Jul 2019 09:53:37 -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=JZ17Zwq5nKyQodcnNqDyBJEdJKZbn+GdcZVs6/zKV5c=; b=yGZ9f+yoUMo8rKGQPxzUrMmHjX kqiaOpwggFt+yaDlnd8y5nQdysmSTxmU63VvSy9M55BN56Dj2m+o4jOlLKuvmcj1mKmNfDFCMsZab PSyvS4o2c0UxkOl14vvE4AM4CyFVdyO7pI2/Oejubq9LpgC6xtVpT6UMklX2uxzc0L2AB0o1ctK1D elDnYqIIL++oiz2p8VBdTEjer+joq/E+KX8qc5PpNzeBwMBE8NVzHXWoC0NFmdBidVDRzX3QbhGLT I0FC3M9OxzOlOgPnJ9MQyzzCoq8o+6fY02unxTvR5bYEPKqZP9AhZiNMfGxZpGJcZLOwbSM5ciUs9 2Ch/JlZQ==; 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-0003u7-GR; Thu, 18 Jul 2019 13:53:26 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 0) id CEBB120B979A5; Thu, 18 Jul 2019 15:53:22 +0200 (CEST) Message-Id: <20190718135206.123357505@infradead.org> User-Agent: quilt/0.65 Date: Thu, 18 Jul 2019 15:49:57 +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, Peter Hurley Subject: [PATCH 3/4] tty/ldsem: Add missing ACQUIRE to read_failed 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 rwsem down_slowpath, Will noticed ldsem had a copy of a bug we just found for rwsem. 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'. Cc: Peter Hurley Fixes: 4898e640caf0 ("tty: Add timed, writer-prioritized rw semaphore") Reported-by: Will Deacon Acked-by: Will Deacon Signed-off-by: Peter Zijlstra (Intel) --- drivers/tty/tty_ldsem.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) --- a/drivers/tty/tty_ldsem.c +++ b/drivers/tty/tty_ldsem.c @@ -93,8 +93,7 @@ static void __ldsem_wake_readers(struct list_for_each_entry_safe(waiter, next, &sem->read_wait, list) { tsk = waiter->task; - smp_mb(); - waiter->task = NULL; + smp_store_release(&waiter->task, NULL); wake_up_process(tsk); put_task_struct(tsk); } @@ -194,7 +193,7 @@ down_read_failed(struct ld_semaphore *se for (;;) { set_current_state(TASK_UNINTERRUPTIBLE); - if (!waiter.task) + if (!smp_load_acquire(&waiter.task)) break; if (!timeout) break;