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=-14.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 F0D5FC4320A for ; Sun, 8 Aug 2021 12:55:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CCBE56101C for ; Sun, 8 Aug 2021 12:55:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230486AbhHHM4E (ORCPT ); Sun, 8 Aug 2021 08:56:04 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43682 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229504AbhHHM4D (ORCPT ); Sun, 8 Aug 2021 08:56:03 -0400 Received: from mail-wm1-x32d.google.com (mail-wm1-x32d.google.com [IPv6:2a00:1450:4864:20::32d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 18E65C061760; Sun, 8 Aug 2021 05:55:43 -0700 (PDT) Received: by mail-wm1-x32d.google.com with SMTP id h24-20020a1ccc180000b029022e0571d1a0so9489004wmb.5; Sun, 08 Aug 2021 05:55:43 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=to:cc:references:from:subject:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=KumXTSRy1ccI0diRB9WIg9PzVSWqHO8LNyHxSxpOrJs=; b=MzW+ITtgPThujFWV0WY9+sTfUnfb7Z+ir0p06CFXCaFQcfXRmwyrl2uxwwQmoJ0QPp QliKo61Y8PgkOH3KfDQbfjtgkYiesATvnXNdoAg0NkxHED4aIp5yuV/zdgPHQ7VYsZIH O3eULSIsSGbrKRJSzq0+UQkBcF6MqRWhIrXQx2jaAu7X03X6ejO8/D/eDkYnILzI356V xbK6V6+0+tt3KPueMEB6/K9sbPTgALTgTxRLAM+27rjzhsEGd77KhtRIOG5iK+bn11RM o8n1drlKg48NnRJq4peJbVLyINErz5Aq7n0NBnTdbPaMdyCIpQHfEe0y5POHbhXujMsu iQCg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:to:cc:references:from:subject:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=KumXTSRy1ccI0diRB9WIg9PzVSWqHO8LNyHxSxpOrJs=; b=epj/SXw+g3CJ76elIFVQMhp4i1fcx+PysI1rMouyx2m7MFd2AcB9OoItbR7KALcG2P ZGH4gx4ccIeqCUYwHkfWFJQYoQW/Olj3DOI7tQNv/Wf7eqiDtwg9Sf8kKsEi6Ib0m9QK dAglg7RGw2b2QUQF5g28k/hoUdTDidBl1hM4ultcnGn1x0wk1IZgZGqzruyWdpyZs7Gd tCCjHsYbMuje598MZkvSQMNrC1U5BxvgXDus8zuXBzwJh98maJUBD67X6Y33Qd1gVZ5q j2u65y0Wbpwk6gvZ3Hzl9hidf/b3bm30v1Lwjf4KSPN8b5osCdr+OxPy1pQrrJ5GxEmT e6TA== X-Gm-Message-State: AOAM531l7xn92uEbcVaZdMTyqEwC148i9g2CDgCNpZkSYy4NgJDiJ3E/ lyOJ2i+wA046NJfOtGj21So= X-Google-Smtp-Source: ABdhPJzcWa7TsLPHPMKznGhYudbIIp0nmOrWESKLxL5ksihDXUjUPVrJOiUkJc8gn7lNKuYvj52vMg== X-Received: by 2002:a1c:f019:: with SMTP id a25mr17834949wmb.96.1628427340979; Sun, 08 Aug 2021 05:55:40 -0700 (PDT) Received: from [192.168.8.197] ([85.255.236.119]) by smtp.gmail.com with ESMTPSA id n3sm14177687wmi.0.2021.08.08.05.55.40 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 08 Aug 2021 05:55:40 -0700 (PDT) To: Nadav Amit , Jens Axboe Cc: io-uring@vger.kernel.org, linux-kernel@vger.kernel.org, Nadav Amit References: <20210808001342.964634-1-namit@vmware.com> <20210808001342.964634-2-namit@vmware.com> From: Pavel Begunkov Subject: Re: [PATCH 1/2] io_uring: clear TIF_NOTIFY_SIGNAL when running task work Message-ID: <488f005c-fd92-9881-2700-b2eb1adbb78e@gmail.com> Date: Sun, 8 Aug 2021 13:55:12 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.12.0 MIME-Version: 1.0 In-Reply-To: <20210808001342.964634-2-namit@vmware.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/8/21 1:13 AM, Nadav Amit wrote: > From: Nadav Amit > > When using SQPOLL, the submission queue polling thread calls > task_work_run() to run queued work. However, when work is added with > TWA_SIGNAL - as done by io_uring itself - the TIF_NOTIFY_SIGNAL remains static int io_req_task_work_add(struct io_kiocb *req) { ... notify = (req->ctx->flags & IORING_SETUP_SQPOLL) ? TWA_NONE : TWA_SIGNAL; if (!task_work_add(tsk, &tctx->task_work, notify)) ... } io_uring doesn't set TIF_NOTIFY_SIGNAL for SQPOLL. But if you see it, I'm rather curious who does. > set afterwards and is never cleared. > > Consequently, when the submission queue polling thread checks whether > signal_pending(), it may always find a pending signal, if > task_work_add() was ever called before. > > The impact of this bug might be different on different kernel versions. > It appears that on 5.14 it would only cause unnecessary calculation and > prevent the polling thread from sleeping. On 5.13, where the bug was > found, it stops the polling thread from finding newly submitted work. > > Instead of task_work_run(), use tracehook_notify_signal() that clears > TIF_NOTIFY_SIGNAL. Test for TIF_NOTIFY_SIGNAL in addition to > current->task_works to avoid a race in which task_works is cleared but > the TIF_NOTIFY_SIGNAL is set. > > Fixes: 685fe7feedb96 ("io-wq: eliminate the need for a manager thread") > Cc: Jens Axboe > Cc: Pavel Begunkov > Signed-off-by: Nadav Amit > --- > fs/io_uring.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/fs/io_uring.c b/fs/io_uring.c > index 5a0fd6bcd318..f39244d35f90 100644 > --- a/fs/io_uring.c > +++ b/fs/io_uring.c > @@ -78,6 +78,7 @@ > #include > #include > #include > +#include > > #define CREATE_TRACE_POINTS > #include > @@ -2203,9 +2204,9 @@ static inline unsigned int io_put_rw_kbuf(struct io_kiocb *req) > > static inline bool io_run_task_work(void) > { > - if (current->task_works) { > + if (test_thread_flag(TIF_NOTIFY_SIGNAL) || current->task_works) { > __set_current_state(TASK_RUNNING); > - task_work_run(); > + tracehook_notify_signal(); > return true; > } > > -- Pavel Begunkov