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=-9.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,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 937E1C3A5A3 for ; Thu, 22 Aug 2019 17:23:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 69B7023427 for ; Thu, 22 Aug 2019 17:23:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1566494621; bh=uZoYPNP9h2RnFw8rgES6mbSeGOZpTQnaYDYan0JsDA4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=YGs0r/iD3UNghosWR53NxYz9xuDbM59y0RlFyLESHPVh/w2Ex83A2ITepen/HLMlD VAzmKyc8dKETII987e9nYu5q7HFSBRc2PnQzeuJWTosBVNGxNvU8kCfcePyQc+gNFT c43OX7IJMFqYjVZDtl7BJ50A5Tf/Gzv1fYq9Et98= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2403988AbfHVRXk (ORCPT ); Thu, 22 Aug 2019 13:23:40 -0400 Received: from mail.kernel.org ([198.145.29.99]:43272 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2403948AbfHVRX0 (ORCPT ); Thu, 22 Aug 2019 13:23:26 -0400 Received: from localhost (wsip-184-188-36-2.sd.sd.cox.net [184.188.36.2]) (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 03BFB23400; Thu, 22 Aug 2019 17:23:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1566494606; bh=uZoYPNP9h2RnFw8rgES6mbSeGOZpTQnaYDYan0JsDA4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=SbZHKv/pI351wURk1BqpzVLA6R7EkLjn+YK3NkYqBh1KNMullqW/mTVczI4UKLfpR KTrSg6LA3SQNkekH+zEwLk6PAxA267a14llNe+6V32dtl7giNPvGCwUAJPVKhGXoI3 sx02ksutdz4miQSYeWcAVlH35hestoGSKemCSYHw= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Will Deacon , "Peter Zijlstra (Intel)" , Linus Torvalds , Peter Hurley , Thomas Gleixner , Ingo Molnar , Sasha Levin Subject: [PATCH 4.9 029/103] tty/ldsem, locking/rwsem: Add missing ACQUIRE to read_failed sleep loop Date: Thu, 22 Aug 2019 10:18:17 -0700 Message-Id: <20190822171730.019752147@linuxfoundation.org> X-Mailer: git-send-email 2.23.0 In-Reply-To: <20190822171728.445189830@linuxfoundation.org> References: <20190822171728.445189830@linuxfoundation.org> User-Agent: quilt/0.66 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 [ 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