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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id F0AA2C77B73 for ; Wed, 31 May 2023 05:23:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234053AbjEaFXV (ORCPT ); Wed, 31 May 2023 01:23:21 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46630 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231314AbjEaFXR (ORCPT ); Wed, 31 May 2023 01:23:17 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D94DA11B for ; Tue, 30 May 2023 22:22:31 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1685510551; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=WEQ7TS+vyvsvSkbc945GTeCJNzt8/T2iPFI6Ja2m7Tc=; b=B5qdfblkVVKKuA/r00eamUpEVrRISfsUxEhRpqkqeKdyC2ygEVvMNkQT7KaPeysnHw0SGX RNL1wG1KKnymrKvnOxZ2LaoVuIM5q5nCMwIABwuxnwBcm4m0fO+7uuRbFi3SMebqVIXAJj Wlyc5pkhT/Nv1YbyN1WZ0xJF4GG6Pb0= Received: from mail-pg1-f199.google.com (mail-pg1-f199.google.com [209.85.215.199]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-641-b6QmNHAJPGiU6rCIa8qxjw-1; Wed, 31 May 2023 01:22:29 -0400 X-MC-Unique: b6QmNHAJPGiU6rCIa8qxjw-1 Received: by mail-pg1-f199.google.com with SMTP id 41be03b00d2f7-53450fa3a18so4670462a12.0 for ; Tue, 30 May 2023 22:22:29 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1685510549; x=1688102549; h=content-transfer-encoding:in-reply-to:from:content-language :references:cc:to:subject:user-agent:mime-version:date:message-id :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=WEQ7TS+vyvsvSkbc945GTeCJNzt8/T2iPFI6Ja2m7Tc=; b=b12gs2+OdWMzlOufJ6M3F8StiGE9a+vqJy2mvjGz8fnDKZOwo9836VUYBDde8DQoLy PY0APVwcdNF8yl4eGXJwdndwsjmmA1tOj6F7ZQsGQhHBNJP8IPXRKZU5FK/JVuPfWO0t teLJAvpPehdR7RCEEVbfWlYol2jV2RYXsQxuq4wMWggPJo+E8RhM1KR+yK1qF0gZ2ZsV Lt8mM85XrIfsidEAr8fQ+RLu5bN+TpcOGYCxa75vM/bnt7u+6e/0OZNGz6NpeFdM4TLz RYbIP5IVnEMuLtCJwLtMJ63qYRUWP7M+H4dxiTDA5HZ2FK+RArdqAzy9JSYZ6rCInqYU NlkA== X-Gm-Message-State: AC+VfDyyroQWyu8b4eOsNQ/5VMhRGFA4BbOos3H7K3tfGerzUKik7Fn6 BICFsv7vIisflaqdESpKKdcDqkM0lqmZmMPZIIFh2BRyxsia4LWCNFB3v7eO09lLWd7ZC9dpuC3 rJDskK28okpIPw2JIlAMfWyLL X-Received: by 2002:a05:6a20:7fa7:b0:105:8173:93a0 with SMTP id d39-20020a056a207fa700b00105817393a0mr6006068pzj.5.1685510548712; Tue, 30 May 2023 22:22:28 -0700 (PDT) X-Google-Smtp-Source: ACHHUZ7u0/KbgtxubOa7ggKO6fzLX5KAxiKr4jwHXNkdUFKNRBJw5oMEaCK0s5MaabHczQzM6Lyt9Q== X-Received: by 2002:a05:6a20:7fa7:b0:105:8173:93a0 with SMTP id d39-20020a056a207fa700b00105817393a0mr6006055pzj.5.1685510548453; Tue, 30 May 2023 22:22:28 -0700 (PDT) Received: from [10.72.13.48] ([209.132.188.80]) by smtp.gmail.com with ESMTPSA id s11-20020aa7828b000000b0063d670ad850sm2582842pfm.92.2023.05.30.22.22.24 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 30 May 2023 22:22:28 -0700 (PDT) Message-ID: <26c87be0-8e19-d677-a51b-e6821e6f7ae4@redhat.com> Date: Wed, 31 May 2023 13:22:22 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.11.0 Subject: Re: [PATCH 3/3] fork, vhost: Use CLONE_THREAD to fix freezer/ps regression To: Oleg Nesterov , Mike Christie Cc: linux@leemhuis.info, nicolas.dichtel@6wind.com, axboe@kernel.dk, ebiederm@xmission.com, torvalds@linux-foundation.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, mst@redhat.com, sgarzare@redhat.com, stefanha@redhat.com, brauner@kernel.org References: <20230522025124.5863-1-michael.christie@oracle.com> <20230522025124.5863-4-michael.christie@oracle.com> <20230522123029.GA22159@redhat.com> <20230522174757.GC22159@redhat.com> <20230523121506.GA6562@redhat.com> Content-Language: en-US From: Jason Wang In-Reply-To: <20230523121506.GA6562@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 在 2023/5/23 20:15, Oleg Nesterov 写道: > On 05/22, Oleg Nesterov wrote: >> Right now I think that "int dead" should die, > No, probably we shouldn't call get_signal() if we have already dequeued SIGKILL. > >> but let me think tomorrow. > May be something like this... I don't like it but I can't suggest anything better > right now. > > bool killed = false; > > for (;;) { > ... > > node = llist_del_all(&worker->work_list); > if (!node) { > schedule(); > /* > * When we get a SIGKILL our release function will > * be called. That will stop new IOs from being queued > * and check for outstanding cmd responses. It will then > * call vhost_task_stop to tell us to return and exit. > */ > if (signal_pending(current)) { > struct ksignal ksig; > > if (!killed) > killed = get_signal(&ksig); > > clear_thread_flag(TIF_SIGPENDING); > } > > continue; > } > > ------------------------------------------------------------------------------- > But let me ask a couple of questions. Let's forget this patch, let's look at the > current code: > > node = llist_del_all(&worker->work_list); > if (!node) > schedule(); > > node = llist_reverse_order(node); > ... process works ... > > To me this looks a bit confusing. Shouldn't we do > > if (!node) { > schedule(); > continue; > } > > just to make the code a bit more clear? If node == NULL then > llist_reverse_order() and llist_for_each_entry_safe() will do nothing. > But this is minor. Yes. > > > > /* make sure flag is seen after deletion */ > smp_wmb(); > llist_for_each_entry_safe(work, work_next, node, node) { > clear_bit(VHOST_WORK_QUEUED, &work->flags); > > I am not sure about smp_wmb + clear_bit. Once we clear VHOST_WORK_QUEUED, > vhost_work_queue() can add this work again and change work->node->next. > > That is why we use _safe, but we need to ensure that llist_for_each_safe() > completes LOAD(work->node->next) before VHOST_WORK_QUEUED is cleared. This should be fine since store is not speculated, so work->node->next needs to be loaded before VHOST_WORK_QUEUED is cleared to meet the loop condition. > So it seems that smp_wmb() can't help and should be removed, instead we need > > llist_for_each_entry_safe(...) { > smp_mb__before_atomic(); > clear_bit(VHOST_WORK_QUEUED, &work->flags); > > Also, if the work->fn pointer is not stable, we should read it before > smp_mb__before_atomic() as well. The fn won't be changed after it is initialized. > > No? > > > __set_current_state(TASK_RUNNING); > > Why do we set TASK_RUNNING inside the loop? Does this mean that work->fn() > can return with current->state != RUNNING ? It is because the state were set to TASK_INTERRUPTIBLE in the beginning of the loop otherwise it might be side effect while executing work->fn(). > > > work->fn(work); > > Now the main question. Whatever we do, SIGKILL/SIGSTOP/etc can come right > before we call work->fn(). Is it "safe" to run this callback with > signal_pending() or fatal_signal_pending() ? It looks safe since: 1) vhost hold refcnt of the mm 2) release will sync with the worker > > > Finally. I never looked into drivers/vhost/ before so I don't understand > this code at all, but let me ask anyway... Can we change vhost_dev_flush() > to run the pending callbacks rather than wait for vhost_worker() ? > I guess we can't, ->mm won't be correct, but can you confirm? Yes. Thanks > > Oleg. >