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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 BD95BC3A5A6 for ; Fri, 30 Aug 2019 15:51:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9296F22CE9 for ; Fri, 30 Aug 2019 15:51:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1567180266; bh=wwQEdvFf9puXsCeLI0z1hKyGaI/Q67p+3sPwRkyyYeE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=QzNGRBUPlMeurlFL/6zcGAdgUHB0OEjvC+O04lhm5iCgR1iwtjkCrmMdaxwayHkL4 nyc+vWM/JcQ/nks+uS6ElmdRf7uSuNeudzd541ZG4vV0behcQjyZsd43UkruYGMDZS ZYVKce7/W5f4YdJnm+HoT/0S7I/0r5D5Ty3IkeuY= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728237AbfH3PvF (ORCPT ); Fri, 30 Aug 2019 11:51:05 -0400 Received: from mail-qt1-f196.google.com ([209.85.160.196]:38924 "EHLO mail-qt1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727135AbfH3PvF (ORCPT ); Fri, 30 Aug 2019 11:51:05 -0400 Received: by mail-qt1-f196.google.com with SMTP id n7so8077372qtb.6; Fri, 30 Aug 2019 08:51:04 -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:user-agent; bh=mgOK+4EfzrzqKzAOXuYJVaIrWdAPC+wCshpIrSxOVWo=; b=lBpuogk7Jq4wq3D79s4tff/roknGXtcgIc5Ej2HHnyKukQw8PRGj4Yqi+jHA4IhXUJ rW88Gef6srA8l/7TOSiRW0OHhKUlnlG7usKems1SicB1+tpxFOaLaAXw+b9IiuL9HLNg GGSvUxZpXMQgi/dvpRiSuq5ERxIAsak//7sO2SmODIUtoXqwDFm13ZzRhDSKchlnXyXP UPsWmMLyd73IJIvZFAXcrVY5XQU9bNRn1nEePBvtH12VdYI92VWHTP3wGuyMm1jiImqM kfxyA9Ddg4mGFAmYW5roOsNjPI3EAmCobHBHYlnT2qGSzZqY6l+OBrkIfTwRQJMf/IIH s3YQ== 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:user-agent; bh=mgOK+4EfzrzqKzAOXuYJVaIrWdAPC+wCshpIrSxOVWo=; b=OIt4dLD+mO4T7H/vvGsf/9meZVzT3rTIL2Da7qYsWLxlA53CQKdbowgC3gUrf3urE9 ieIAqMZLo2pf0WKJrp2BkmL48+qigoa1sGp16UTcfT0jO9mft9WEWQdK41xp+Wi4Xf6W TY7aXpmPmONr7wlh+wBB0/rapsVOn2EfJNn/U7VrwaSOmjT+5oXKmANQM8KIJl39dcqw 9+2Oqno7cPl0/AAFcdHdVJy6siQreGgszQPdOr+wgB88TrftM0JbSgfBcfyVa3PFfYRC 52mijx8Qs8Lyzf/MO0xFwfFGSJCHbBtV5g7MX1UsABi3cqfiRAv7fT34cOC/7OVa07FH jknw== X-Gm-Message-State: APjAAAXHJhdl8YyPHp45QfFglCb8HtVAQ2OF2yJY2iI6g3FT8wxEvMTw 13BsyI+I3AVQVvD3e+QO6C0= X-Google-Smtp-Source: APXvYqxWLLbDQHb495M0qaRjsinqF4egCG84dCcabK1WCpU8rv75mI9EsdOe/lr6lb8vsmI2IK0JOg== X-Received: by 2002:ac8:7504:: with SMTP id u4mr15187775qtq.81.1567180263853; Fri, 30 Aug 2019 08:51:03 -0700 (PDT) Received: from localhost ([2620:10d:c091:480::d0dd]) by smtp.gmail.com with ESMTPSA id s4sm2782788qkb.130.2019.08.30.08.51.02 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 30 Aug 2019 08:51:03 -0700 (PDT) Date: Fri, 30 Aug 2019 08:51:01 -0700 From: Tejun Heo To: Jan Kara Cc: Jens Axboe , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH block/for-next] writeback: add tracepoints for cgroup foreign writebacks Message-ID: <20190830155101.GA2263813@devbig004.ftw2.facebook.com> References: <20190829224701.GX2263813@devbig004.ftw2.facebook.com> <20190830154023.GC25069@quack2.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190830154023.GC25069@quack2.suse.cz> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 30, 2019 at 05:40:23PM +0200, Jan Kara wrote: > Are the page dereferences above safe? I suppose lock_page_memcg() protects > the page->mem_cgroup->css.cgroup->kn->id dereference? But page->mapping > does not seem to be protected by page lock? Forgot to respond to the mem_cgroup part. The page to memcg association never changes on cgroup2 as long as the page has ref, so I think that one should be safe. Thanks. -- tejun