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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 776AFC433F5 for ; Mon, 27 Sep 2021 15:41:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 59CE060F3A for ; Mon, 27 Sep 2021 15:41:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234622AbhI0Pn2 (ORCPT ); Mon, 27 Sep 2021 11:43:28 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46402 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234500AbhI0Pn2 (ORCPT ); Mon, 27 Sep 2021 11:43:28 -0400 Received: from mail-io1-xd36.google.com (mail-io1-xd36.google.com [IPv6:2607:f8b0:4864:20::d36]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 11B66C061575 for ; Mon, 27 Sep 2021 08:41:50 -0700 (PDT) Received: by mail-io1-xd36.google.com with SMTP id d18so23245629iof.13 for ; Mon, 27 Sep 2021 08:41:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel-dk.20210112.gappssmtp.com; s=20210112; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=yR41MoTNkU9al4z4GT+fAfxfygf7dAvJSNsFx2wrpz4=; b=wHEnHbxFc7Q0qFcxX9sdp9goT9A4sK7ttDI6U5aZ9FWoAa0J5O30GerYq84KPSNNIO MJR+Q2O+sPPETf20IresTjRGGq/5dhg9LDOKDVElTVBFKmzo8IIalgfDg6iJnehvi4dr vLj0qu7q3ZvSA6dqSl0hpS44qBm7mLoXehkDx1fKLfO2m9i51fDUMyaeiFUlB0m4jwEQ Td3nOEncGzFE4ZCzTbfbA/OFhPpZ5i7nQSOiQFWIPCyFF+Ol7Qbl79c08xP6ImMIIqbG nzvNwRqMask0tMSDejokO8Dx5IhR1DPzWawM5enJUc3izQ5basDSrzgTj6Nj0J9TYhUY JXwg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=yR41MoTNkU9al4z4GT+fAfxfygf7dAvJSNsFx2wrpz4=; b=vlWaf+kZ5293Fd2Xsia3WS65V1khfQL0UzVMb0FpzGWPEGzahB310cMB9BI4EHi/7p 6hjn/O4J5DJKYvWq9fnhg8rok9bRY+1QQwH+V3KyZWoy2W65HVnZ/JdczQChv9aR/rzK ENENR6xxbiVayn46HmDcRUI8rel/7gAL/MbtKb2M9if4IQlnwS4d102cXv51cRiDEF+0 X3k81kfJzfLylF7dXCgcsq8x0AEL+drl6u8M+STY8mj/En8ymv7p30iHafJh8gFPe008 nWFrg7xVd3JmZe3EgQpwom+9U9A1MXlIqpIdqN0NZa1ntL+7olUng3W6h1KCCA6H9Lfu kNSg== X-Gm-Message-State: AOAM531hxE89d7tuZKEpofnV4LqR0t2YqJZfMEYEJyKNlXRz+KsH9uru Yedb4PymsuVuimV0ewR7Vp6qj0oxMsONqQ8Qya4= X-Google-Smtp-Source: ABdhPJwgSQJA8KX7h0RRJYpOeS3n1NB8pZRKeijfKI4LWd16YKdLk/lQfeZ6mZoWCUKUDFRGoCA5nQ== X-Received: by 2002:a5d:9d59:: with SMTP id k25mr289458iok.70.1632757309191; Mon, 27 Sep 2021 08:41:49 -0700 (PDT) Received: from [192.168.1.30] ([207.135.234.126]) by smtp.gmail.com with ESMTPSA id y6sm9201640ilv.71.2021.09.27.08.41.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 27 Sep 2021 08:41:48 -0700 (PDT) Subject: Re: [GIT PULL] io_uring fixes for 5.15-rc3 To: "Eric W. Biederman" Cc: Linus Torvalds , Oleg Nesterov , Al Viro , io-uring References: <0eeefd32-f322-1470-9bcf-0f415be517bd@kernel.dk> <87lf3iazyu.fsf@disp2133> <521162e9-c7e4-284e-e575-51c503c51793@kernel.dk> <878rzi831l.fsf@disp2133> From: Jens Axboe Message-ID: Date: Mon, 27 Sep 2021 09:41:48 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <878rzi831l.fsf@disp2133> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 9/27/21 9:13 AM, Eric W. Biederman wrote: > Jens Axboe writes: > >> On 9/27/21 8:29 AM, Jens Axboe wrote: >>> On 9/27/21 7:51 AM, Eric W. Biederman wrote: >>>> Jens Axboe writes: >>>> >>>>> On 9/25/21 5:05 PM, Linus Torvalds wrote: >>>>>> On Sat, Sep 25, 2021 at 1:32 PM Jens Axboe wrote: >>>>>>> >>>>>>> - io-wq core dump exit fix (me) >>>>>> >>>>>> Hmm. >>>>>> >>>>>> That one strikes me as odd. >>>>>> >>>>>> I get the feeling that if the io_uring thread needs to have that >>>>>> signal_group_exit() test, something is wrong in signal-land. >>>>>> >>>>>> It's basically a "fatal signal has been sent to another thread", and I >>>>>> really get the feeling that "fatal_signal_pending()" should just be >>>>>> modified to handle that case too. >>>>> >>>>> It did surprise me as well, which is why that previous change ended up >>>>> being broken for the coredump case... You could argue that the io-wq >>>>> thread should just exit on signal_pending(), which is what we did >>>>> before, but that really ends up sucking for workloads that do use >>>>> signals for communication purposes. postgres was the reporter here. >>>> >>>> The primary function get_signal is to make signals not pending. So I >>>> don't understand any use of testing signal_pending after a call to >>>> get_signal. >>>> >>>> My confusion doubles when I consider the fact io_uring threads should >>>> only be dequeuing SIGSTOP and SIGKILL. >>>> >>>> I am concerned that an io_uring thread that dequeues SIGKILL won't call >>>> signal_group_exit and thus kill the other threads in the thread group. >>>> >>>> What motivated removing the break and adding the fatal_signal_pending >>>> test? >>> >>> I played with this a bit this morning, and I agree it doesn't seem to be >>> needed at all. The original issue was with postgres, I'll give that a >>> whirl as well and see if we run into any unwarranted exits. My simpler >>> test case did not. >> >> Ran the postgres test, and we get tons of io-wq exiting on get_signal() >> returning true. Took a closer look, and it actually looks very much >> expected, as it's a SIGKILL to the original task. >> >> So it looks like I was indeed wrong, and this probably masked the >> original issue that was fixed in that series. I've been running with >> this: >> >> diff --git a/fs/io-wq.c b/fs/io-wq.c >> index c2360cdc403d..afd1db8e000d 100644 >> --- a/fs/io-wq.c >> +++ b/fs/io-wq.c >> @@ -584,10 +584,9 @@ static int io_wqe_worker(void *data) >> >> if (!get_signal(&ksig)) >> continue; >> - if (fatal_signal_pending(current) || >> - signal_group_exit(current->signal)) >> - break; >> - continue; >> + if (ksig.sig != SIGKILL) >> + printk("exit on sig! fatal? %d, sig=%d\n", fatal_signal_pending(current), ksig.sig); >> + break; >> } >> last_timeout = !ret; >> } >> >> and it's running fine and, as expected, we don't generate any printk >> activity as these are all fatal deliveries to the parent. > > Good. So just a break should be fine. Indeed, I'll send out a patch for that. > A little bit of me is concerned about not calling do_group_exit in this > case. Fortunately it is not a problem as complete_signal kills all of > the threads in a signal_group when SIGKILL is delivered. > > So at least until something else is refactored and io_uring threads > unblock another fatal signal all is well. Should we put a comment in io-wq to that effect? I don't see why we'd ever unblock other signals there, but... -- Jens Axboe