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 33E30C433FE for ; Mon, 27 Sep 2021 15:52:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1F6CC6108E for ; Mon, 27 Sep 2021 15:52:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235100AbhI0PyS (ORCPT ); Mon, 27 Sep 2021 11:54:18 -0400 Received: from out03.mta.xmission.com ([166.70.13.233]:37860 "EHLO out03.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235307AbhI0PyR (ORCPT ); Mon, 27 Sep 2021 11:54:17 -0400 Received: from in02.mta.xmission.com ([166.70.13.52]:33456) by out03.mta.xmission.com with esmtps (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1mUsvm-00HYwN-GR; Mon, 27 Sep 2021 09:52:38 -0600 Received: from ip68-227-160-95.om.om.cox.net ([68.227.160.95]:56866 helo=email.xmission.com) by in02.mta.xmission.com with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1mUsvl-00ElU9-Ao; Mon, 27 Sep 2021 09:52:38 -0600 From: ebiederm@xmission.com (Eric W. Biederman) To: Jens Axboe 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> Date: Mon, 27 Sep 2021 10:52:03 -0500 In-Reply-To: (Jens Axboe's message of "Mon, 27 Sep 2021 09:41:48 -0600") Message-ID: <87wnn26mos.fsf@disp2133> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-SPF: eid=1mUsvl-00ElU9-Ao;;;mid=<87wnn26mos.fsf@disp2133>;;;hst=in02.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX1/DPov77KEizP5m4Wxy4XhQGizZZYZrjnw= X-SA-Exim-Connect-IP: 68.227.160.95 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Re: [GIT PULL] io_uring fixes for 5.15-rc3 X-SA-Exim-Version: 4.2.1 (built Sat, 08 Feb 2020 21:53:50 +0000) X-SA-Exim-Scanned: Yes (on in02.mta.xmission.com) Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org Jens Axboe writes: > 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... I suspect rather we should update this comment in get_signal instead. /* * PF_IO_WORKER threads will catch and exit on fatal signals * themselves. They have cleanup that must be performed, so * we cannot call do_exit() on their behalf. */ if (current->flags & PF_IO_WORKER) goto out; Although I would not mind updating io-wq.c and io_uring.c where they call get_signal as well. Eric