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=-26.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_GIT,USER_IN_DEF_DKIM_WL 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 BF031C4320A for ; Mon, 30 Aug 2021 17:30:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 964AE60F44 for ; Mon, 30 Aug 2021 17:30:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238075AbhH3Ray (ORCPT ); Mon, 30 Aug 2021 13:30:54 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35058 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229709AbhH3Raw (ORCPT ); Mon, 30 Aug 2021 13:30:52 -0400 Received: from mail-pj1-x104a.google.com (mail-pj1-x104a.google.com [IPv6:2607:f8b0:4864:20::104a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 02284C06175F for ; Mon, 30 Aug 2021 10:29:59 -0700 (PDT) Received: by mail-pj1-x104a.google.com with SMTP id fy13-20020a17090b020d00b001939890b4d6so1972353pjb.8 for ; Mon, 30 Aug 2021 10:29:58 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:message-id:mime-version:subject:from:to:cc; bh=LVV3UHlk75yje1xXSFFRWyfRbrh8OImERx560ZLqV78=; b=IvtVU2ecU6KZCoDqCW093hiZ2lhwtQIofFW8UZrOYtk+4S6cXBZM8LYiHxTLo4DA62 Mcsr5juVYUrOy8rNyG1yZ7voTbgtLZowhpm4tnGY655pEJvnJp7fyMZTqiMH1sQS94hr 9UX3sA2Bb364oAvBYogFtLGQ1YCTDOAgIbFSxHqXCrfUwhq49GCKEQbLyH/0HeZAZCCH T5ilQHDzPuxCXeyzVeQjK6gBJHf4UkTwnOl2zR/K51CKwqjq2xQmcZYfaxYnOM37SYRS 8CIAN6O9Bq5BWHogtAPODwYydCw1lsWmC5+GKMkgJl7k0H6KCXzSLTMvK8Mejsyaoirg ajVA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:message-id:mime-version:subject:from:to:cc; bh=LVV3UHlk75yje1xXSFFRWyfRbrh8OImERx560ZLqV78=; b=Z+UcFiTHnfyxvPnbjeEoVBBFsklFqZGNwoRUSUQBePMKJarDY2C3VnZTDmafl5+tGI htUC9mX7fhyhjxtJMFUBbQd4C3E9DV6M0oX0qFJMPbW5A7FfQfCetQJpLwx6QaQ8ZR4a Pb1jITzgM5LT+s7gzQccoDDHzkhlOQZjLmPBVQy3lAsltfXmK68vWu9iO/Cy9FjHYdIl oAxF/i0HoXUs1WJX46coywlcuCHU51Tb40/8uoP7zpTVadKOrFyUaLA0klx2TXQKrGgK QJIb7+g8rno28fmTfUamSHv0ozCAOdJvWYHMq3geqVeqefcVQgkPIfTRtPUvrq4mChZS 7Obw== X-Gm-Message-State: AOAM5303Ewege3kXezf7Y2xeYNYHUEQdvv/QAl/aTqFgnAPDTIdluxH6 h2fahlC/RXBucl5PDGreuPkIXL6sfdr1Bw== X-Google-Smtp-Source: ABdhPJzCcC4VvlzbbigWq9Ik0NqIKJYOOVsEeFdC4+tI++PBliuKJgwEngIraYu+cMozuc9V7j3OEuD8/wksKQ== X-Received: from shakeelb.svl.corp.google.com ([2620:15c:2cd:202:cc09:9ca3:397b:a20c]) (user=shakeelb job=sendgmr) by 2002:a65:6658:: with SMTP id z24mr22641670pgv.266.1630344598441; Mon, 30 Aug 2021 10:29:58 -0700 (PDT) Date: Mon, 30 Aug 2021 10:29:53 -0700 Message-Id: <20210830172953.207257-1-shakeelb@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.33.0.259.gc128427fd7-goog Subject: [PATCH] memcg: make memcg->event_list_lock irqsafe From: Shakeel Butt To: Tejun Heo , Johannes Weiner , Michal Hocko Cc: Andrew Morton , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Shakeel Butt Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The memcg->event_list_lock is usually taken in the normal context but when the userspace closes the corresponding eventfd, eventfd_release through memcg_event_wake takes memcg->event_list_lock with interrupts disabled. This is not an issue on its own but it creates a nested dependency from eventfd_ctx->wqh.lock to memcg->event_list_lock. Independently, for unrelated eventfd, eventfd_signal() can be called in the irq context, thus making eventfd_ctx->wqh.lock an irq lock. For example, FPGA DFL driver, VHOST VPDA driver and couple of VFIO drivers. This will force memcg->event_list_lock to be an irqsafe lock as well. One way to break the nested dependency between eventfd_ctx->wqh.lock and memcg->event_list_lock is to add an indirection. However the simplest solution would be to make memcg->event_list_lock irqsafe. This is cgroup v1 feature, is in maintenance and may get deprecated in near future. So, no need to add more code. BTW this has been discussed previously [1] but there weren't irq users of eventfd_signal() at the time. [1] https://www.spinics.net/lists/cgroups/msg06248.html Signed-off-by: Shakeel Butt --- mm/memcontrol.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 999e626f4111..a73689caee5d 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -4851,9 +4851,9 @@ static ssize_t memcg_write_event_control(struct kernfs_open_file *of, vfs_poll(efile.file, &event->pt); - spin_lock(&memcg->event_list_lock); + spin_lock_irq(&memcg->event_list_lock); list_add(&event->list, &memcg->event_list); - spin_unlock(&memcg->event_list_lock); + spin_unlock_irq(&memcg->event_list_lock); fdput(cfile); fdput(efile); @@ -5280,12 +5280,12 @@ static void mem_cgroup_css_offline(struct cgroup_subsys_state *css) * Notify userspace about cgroup removing only after rmdir of cgroup * directory to avoid race between userspace and kernelspace. */ - spin_lock(&memcg->event_list_lock); + spin_lock_irq(&memcg->event_list_lock); list_for_each_entry_safe(event, tmp, &memcg->event_list, list) { list_del_init(&event->list); schedule_work(&event->remove); } - spin_unlock(&memcg->event_list_lock); + spin_unlock_irq(&memcg->event_list_lock); page_counter_set_min(&memcg->memory, 0); page_counter_set_low(&memcg->memory, 0); -- 2.33.0.259.gc128427fd7-goog