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=-9.0 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,INCLUDES_CR_TRAILER,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 8BCE4C4338F for ; Tue, 27 Jul 2021 23:13:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 65F4D60249 for ; Tue, 27 Jul 2021 23:13:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232986AbhG0XN2 (ORCPT ); Tue, 27 Jul 2021 19:13:28 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56718 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232314AbhG0XNZ (ORCPT ); Tue, 27 Jul 2021 19:13:25 -0400 Received: from mail-pj1-x1036.google.com (mail-pj1-x1036.google.com [IPv6:2607:f8b0:4864:20::1036]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 22551C061757; Tue, 27 Jul 2021 16:13:24 -0700 (PDT) Received: by mail-pj1-x1036.google.com with SMTP id b6so2266101pji.4; Tue, 27 Jul 2021 16:13:24 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=IJH4q6xKknpFCnME1MQ4rrc80QVCXZj1Kd8DIZ0/IhQ=; b=RDDPk3g21uOn+gvEHvobhce6lQTn5Mq7nQNxDeFycx7c7RXn4xjZnyH/omdaeMk+O3 bFAWs+7yxxqhCqLCMsJ9sgGr14Zxo6uVYqApMj6C2S+6L0Bw7EBgdo1njMLa8WAV8j9J Ydz92yY4SQZTpCctVQbhovhNiiHXHyRauzBeaWX0GqXod0tb7Hdi6/G0wflkCGXrHI55 7IpHNYSWY2V4emWWdKAT8srhjlCD2DbZUZKyDpHDOxKfYjQLd/nXsOKBJ8Qq2NvtGlT6 kmNTnk0xrhQsqfyd8Hho/kLvsqw+ahDCLptTC8ne7eLn7FTy7xsE1rioaqbOe64k++oF Ku2Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:from:to:cc:subject:message-id :references:mime-version:content-disposition:in-reply-to; bh=IJH4q6xKknpFCnME1MQ4rrc80QVCXZj1Kd8DIZ0/IhQ=; b=o03IGDPAbzEQXslSu1Z0+9r1Sbb6QCM72eJrQOVq+NZ9Mjfsv73e9EJnRl5xsuNrMi vbArEfdKcYrDXgVykLiSPtx7o8CaWZGqx83NazNr0uebtTXQnwMfq5QRCvtOGkQIXhFq wpRWHHMZVz9NeswJpm34KuKncDT/+379GmBAuc8JED//ONxFBPjmWPlWKU8vZkHnQrq4 Ja0nYzHkxjkHffcDPBfPtYXcBu1Ty/7NXMDnFKi66PLLx8Dgtd7n/sOb4CO7njFfA5pD DIoKUarcRrTjoLKf/34q5YVPiSsJW/4b0z/8YjdkkNXvfGdwNrxU8nk7ZphZz+heoct5 VcoQ== X-Gm-Message-State: AOAM530I6QVprKcJJ5YzZly+Z6a+6HVKSwmc2YyupbrlPDNrF6iqqbes x14Q9AIrhVwAkccbojqmn2VyNkN9VBo= X-Google-Smtp-Source: ABdhPJw7ZJUYZvGDREE8f3L7AQhb0lBZFKoBC+rMUzXEn0SUupttLTCzixCk4o5VCsGhaE+mAvbqkA== X-Received: by 2002:a63:d311:: with SMTP id b17mr25427653pgg.332.1627427603103; Tue, 27 Jul 2021 16:13:23 -0700 (PDT) Received: from localhost (udp264798uds.hawaiiantel.net. [72.253.242.87]) by smtp.gmail.com with ESMTPSA id x189sm5563989pfx.99.2021.07.27.16.13.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 27 Jul 2021 16:13:22 -0700 (PDT) Sender: Tejun Heo Date: Tue, 27 Jul 2021 13:13:21 -1000 From: Tejun Heo To: cgroups@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Rik van Riel Subject: Re: [PATCH cgroup/for-5.14-fixes] cgroup: rstat: fix A-A deadlock on 32bit around u64_stats_sync Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 27, 2021 at 01:04:49PM -1000, Tejun Heo wrote: > 0fa294fb1985 ("cgroup: Replace cgroup_rstat_mutex with a spinlock") added > cgroup_rstat_flush_irqsafe() allowing flushing to happen from the irq > context. However, rstat paths use u64_stats_sync to synchronize access to > 64bit stat counters on 32bit machines. u64_stats_sync is implemented using > seq_lock and trying to read from an irq context can lead to A-A deadlock if > the irq happens to interrupt the stat update. > > Fix it by using the irqsafe variants - u64_stats_update_begin_irqsave() and > u64_stats_update_end_irqrestore() - in the update paths. Note that none of > this matters on 64bit machines. All these are just for 32bit SMP setups. > > Signed-off-by: Tejun Heo > Reported-by: Rik van Riel Applying this to cgroup/for-5.14-fixes with stable tag added. Thanks. -- tejun