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=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,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 3F210C433FF for ; Fri, 2 Aug 2019 13:26:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 13B9D217D6 for ; Fri, 2 Aug 2019 13:26:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1564752400; bh=6qK9OVy4Pzr/sOJfb0SO2JV/uW04oNG6W7YR1nTxNwg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=HdddZ0gIG+J18Sw8ytr1xcCA2/HrtC9PknrtPWupPm0dZApEXG+rmfTme/WwDPW09 IZCGxLaleczJxZxhZw0RhCuPKFbSWkq/5ufy8ri3Rg+9MperWd24VmXuYBnWUGsoLn P8k2+3nJ93aUApeUzA1kAitx4vlkKShNvRXHADz4= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2394613AbfHBN0j (ORCPT ); Fri, 2 Aug 2019 09:26:39 -0400 Received: from mail.kernel.org ([198.145.29.99]:37272 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2394586AbfHBN0a (ORCPT ); Fri, 2 Aug 2019 09:26:30 -0400 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id B3420217D6; Fri, 2 Aug 2019 13:26:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1564752388; bh=6qK9OVy4Pzr/sOJfb0SO2JV/uW04oNG6W7YR1nTxNwg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=MJMBeLXwexeOC7KyVbIpXlK72YHXtys7Xa884vXQWJWLYsTNUmQIeOy9z/OovmxRU LAZo3+Ia4sdpeNJR/mYzaxRALWNqDUIrWK5fU61rPghstgQYYcHXiVwTrFUE3GQW1Q XendZVKZOyper99Mcr0IRVlB2vzQYyr7D3Hz+OzM= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Peter Zijlstra , Will Deacon , Linus Torvalds , Peter Hurley , Thomas Gleixner , Ingo Molnar , Sasha Levin Subject: [PATCH AUTOSEL 4.9 21/22] tty/ldsem, locking/rwsem: Add missing ACQUIRE to read_failed sleep loop Date: Fri, 2 Aug 2019 09:25:45 -0400 Message-Id: <20190802132547.14517-21-sashal@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190802132547.14517-1-sashal@kernel.org> References: <20190802132547.14517-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Peter Zijlstra [ Upstream commit 952041a8639a7a3a73a2b6573cb8aa8518bc39f8 ] 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'. Reported-by: Will Deacon Signed-off-by: Peter Zijlstra (Intel) Acked-by: Will Deacon Cc: Linus Torvalds Cc: Peter Hurley Cc: Peter Zijlstra Cc: Thomas Gleixner Fixes: 4898e640caf0 ("tty: Add timed, writer-prioritized rw semaphore") Signed-off-by: Ingo Molnar Signed-off-by: Sasha Levin --- drivers/tty/tty_ldsem.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/drivers/tty/tty_ldsem.c b/drivers/tty/tty_ldsem.c index dbd7ba32caac3..6c5eb99fcfcee 100644 --- a/drivers/tty/tty_ldsem.c +++ b/drivers/tty/tty_ldsem.c @@ -137,8 +137,7 @@ static void __ldsem_wake_readers(struct ld_semaphore *sem) 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); } @@ -234,7 +233,7 @@ down_read_failed(struct ld_semaphore *sem, long count, long timeout) for (;;) { set_task_state(tsk, TASK_UNINTERRUPTIBLE); - if (!waiter.task) + if (!smp_load_acquire(&waiter.task)) break; if (!timeout) break; -- 2.20.1