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=-13.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 87CBEC433F5 for ; Mon, 13 Sep 2021 11:30:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6302461029 for ; Mon, 13 Sep 2021 11:30:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239348AbhIMLb7 (ORCPT ); Mon, 13 Sep 2021 07:31:59 -0400 Received: from mail.kernel.org ([198.145.29.99]:35124 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239327AbhIMLb6 (ORCPT ); Mon, 13 Sep 2021 07:31:58 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id A31AC60F44; Mon, 13 Sep 2021 11:30:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1631532643; bh=vyobawopszv9QS1XVMZ8sClYsg31hVpVDwnmKa1D70g=; h=Subject:To:Cc:From:Date:From; b=E7CZrL8Fz9NE5kuP62kFCrKRCr/W4ofRRj7g0TZSQYh4uncz26j/NvBdZGS9JksjI zLmiH59JXmwlVnZxxxBpv4qspm2ZeoX6382HoP61uF6L0HksREMS8JoTvRV/f7jr5a FUUbqosVf20U2zgi8JbDpQJ9/S4ZUzwn2hHZk+jE= Subject: FAILED: patch "[PATCH] io-wq: fix wakeup race when adding new work" failed to apply to 5.14-stable tree To: axboe@kernel.dk, andres@anarazel.de Cc: From: Date: Mon, 13 Sep 2021 13:30:40 +0200 Message-ID: <163153264022411@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org The patch below does not apply to the 5.14-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From 87df7fb922d18e96992aa5e824aa34b2065fef59 Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Mon, 30 Aug 2021 07:45:47 -0600 Subject: [PATCH] io-wq: fix wakeup race when adding new work When new work is added, io_wqe_enqueue() checks if we need to wake or create a new worker. But that check is done outside the lock that otherwise synchronizes us with a worker going to sleep, so we can end up in the following situation: CPU0 CPU1 lock insert work unlock atomic_read(nr_running) != 0 lock atomic_dec(nr_running) no wakeup needed Hold the wqe lock around the "need to wakeup" check. Then we can also get rid of the temporary work_flags variable, as we know the work will remain valid as long as we hold the lock. Cc: stable@vger.kernel.org Reported-by: Andres Freund Signed-off-by: Jens Axboe diff --git a/fs/io-wq.c b/fs/io-wq.c index 13aeb48a0964..cd9bd095fb1b 100644 --- a/fs/io-wq.c +++ b/fs/io-wq.c @@ -794,7 +794,7 @@ static void io_wqe_insert_work(struct io_wqe *wqe, struct io_wq_work *work) static void io_wqe_enqueue(struct io_wqe *wqe, struct io_wq_work *work) { struct io_wqe_acct *acct = io_work_get_acct(wqe, work); - int work_flags; + bool do_wake; /* * If io-wq is exiting for this task, or if the request has explicitly @@ -806,14 +806,14 @@ static void io_wqe_enqueue(struct io_wqe *wqe, struct io_wq_work *work) return; } - work_flags = work->flags; raw_spin_lock(&wqe->lock); io_wqe_insert_work(wqe, work); wqe->flags &= ~IO_WQE_FLAG_STALLED; + do_wake = (work->flags & IO_WQ_WORK_CONCURRENT) || + !atomic_read(&acct->nr_running); raw_spin_unlock(&wqe->lock); - if ((work_flags & IO_WQ_WORK_CONCURRENT) || - !atomic_read(&acct->nr_running)) + if (do_wake) io_wqe_wake_worker(wqe, acct); }