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=-17.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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=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 43FE6C433C1 for ; Thu, 25 Mar 2021 13:57:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1800861A1F for ; Thu, 25 Mar 2021 13:57:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231195AbhCYN4m (ORCPT ); Thu, 25 Mar 2021 09:56:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43700 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230115AbhCYN4m (ORCPT ); Thu, 25 Mar 2021 09:56:42 -0400 Received: from hr2.samba.org (hr2.samba.org [IPv6:2a01:4f8:192:486::2:0]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F343EC06174A; Thu, 25 Mar 2021 06:56:38 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=samba.org; s=42; h=Date:Message-ID:From:Cc:To; bh=BzjlpMJ8U9y+9nVljOOXA5PT0ZC0uN8Sxr5R9mGjEKk=; b=ZOiEDmm9nEKdS58oOJVHND1vkm zMtFxNAY9Lj9LUDnVEb6MGC7uvDlqu/vjHZ1ibIAOVGJE/wwaybF6IjeU0FCA0OXnr8j3OY5Wj53P bKBW6VHeGIfat7xYFg0lLyqacLCveWWXuS1gHHbbCoOM3IZiC6kxKd2vFh4vZxyk0UFA3MXqYrFle 3vVnsuLeh2XhiDblZUt+XxV3v8okvZp/WCqdlSSeQdMj+LwDVcbKYdRQ1c3uwxuvhXHFR02QUgHeT Etrs7Wo5AJfmmtfMuXkiNbxNULPwJx+7wcwrXIr6lx6ZLeeufg9Z8Dvc/NCacH+q3ZpAoOEiHJv2T IYkRaibfa0lquWD2QiaX3sNX/1do5tAW6mSm4WaWxSZoKQQdEPuvWAEvTOCpEurfh2AuZBlqVFZi9 Aqw2HsexglSHHI08VMFdSgBkCw5Lzy0w17o+sj9XTiNrnVvZGnsM83N7QbVW/Sd/sr8LosMRfzXX3 fj9JSwRtx2OGwpja8xevUZ07; Received: from [127.0.0.2] (localhost [127.0.0.1]) by hr2.samba.org with esmtpsa (TLS1.3:ECDHE_RSA_CHACHA20_POLY1305:256) (Exim) id 1lPQTU-0000Cs-8D; Thu, 25 Mar 2021 13:56:36 +0000 Subject: Re: [PATCH AUTOSEL 5.11 43/44] signal: don't allow STOP on PF_IO_WORKER threads To: Jens Axboe , "Eric W. Biederman" Cc: Sasha Levin , linux-kernel@vger.kernel.org, stable@vger.kernel.org, io-uring , Linus Torvalds References: <20210325112459.1926846-1-sashal@kernel.org> <20210325112459.1926846-43-sashal@kernel.org> <41589c56-9219-3ec2-55b3-3f010752ac7b@samba.org> <2b2a9701-cbe0-4538-ed3b-6917b85bebf8@kernel.dk> From: Stefan Metzmacher Message-ID: Date: Thu, 25 Mar 2021 14:56:34 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 MIME-Version: 1.0 In-Reply-To: <2b2a9701-cbe0-4538-ed3b-6917b85bebf8@kernel.dk> 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 Am 25.03.21 um 14:38 schrieb Jens Axboe: > On 3/25/21 6:11 AM, Stefan Metzmacher wrote: >> >> Am 25.03.21 um 13:04 schrieb Eric W. Biederman: >>> Stefan Metzmacher writes: >>> >>>> Am 25.03.21 um 12:24 schrieb Sasha Levin: >>>>> From: "Eric W. Biederman" >>>>> >>>>> [ Upstream commit 4db4b1a0d1779dc159f7b87feb97030ec0b12597 ] >>>>> >>>>> Just like we don't allow normal signals to IO threads, don't deliver a >>>>> STOP to a task that has PF_IO_WORKER set. The IO threads don't take >>>>> signals in general, and have no means of flushing out a stop either. >>>>> >>>>> Longer term, we may want to look into allowing stop of these threads, >>>>> as it relates to eg process freezing. For now, this prevents a spin >>>>> issue if a SIGSTOP is delivered to the parent task. >>>>> >>>>> Reported-by: Stefan Metzmacher >>>>> Signed-off-by: Jens Axboe >>>>> Signed-off-by: "Eric W. Biederman" >>>>> Signed-off-by: Sasha Levin >>>>> --- >>>>> kernel/signal.c | 3 ++- >>>>> 1 file changed, 2 insertions(+), 1 deletion(-) >>>>> >>>>> diff --git a/kernel/signal.c b/kernel/signal.c >>>>> index 55526b941011..00a3840f6037 100644 >>>>> --- a/kernel/signal.c >>>>> +++ b/kernel/signal.c >>>>> @@ -288,7 +288,8 @@ bool task_set_jobctl_pending(struct task_struct *task, unsigned long mask) >>>>> JOBCTL_STOP_SIGMASK | JOBCTL_TRAPPING)); >>>>> BUG_ON((mask & JOBCTL_TRAPPING) && !(mask & JOBCTL_PENDING_MASK)); >>>>> >>>>> - if (unlikely(fatal_signal_pending(task) || (task->flags & PF_EXITING))) >>>>> + if (unlikely(fatal_signal_pending(task) || >>>>> + (task->flags & (PF_EXITING | PF_IO_WORKER)))) >>>>> return false; >>>>> >>>>> if (mask & JOBCTL_STOP_SIGMASK) >>>>> >>>> >>>> Again, why is this proposed for 5.11 and 5.10 already? >>> >>> Has the bit about the io worker kthreads been backported? >>> If so this isn't horrible. If not this is nonsense. > > No not yet - my plan is to do that, but not until we're 100% satisfied > with it. Do you understand why the patches where autoselected for 5.11 and 5.10? >> I don't know, I hope not... >> >> But I just tested v5.12-rc4 and attaching to >> an application with iothreads with gdb is still not possible, >> it still loops forever trying to attach to the iothreads. > > I do see the looping, gdb apparently doesn't give up when it gets > -EPERM trying to attach to the threads. Which isn't really a kernel > thing, but: Maybe we need to remove the iothreads from /proc/pid/tasks/ >> And I tested 'kill -9 $pidofiothread', and it feezed the whole >> machine... > > that sounds very strange, I haven't seen anything like that running > the exact same scenario. > >> So there's still work to do in order to get 5.12 stable. >> >> I'm short on time currently, but I hope to send more details soon. > > Thanks! I'll play with it this morning and see if I can provoke > something odd related to STOP/attach. Thanks! Somehow I have the impression that your same_thread_group_account patch may fix a lot of things... metze