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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 2A6DEC3A5A8 for ; Mon, 2 Sep 2019 09:05:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F2BC6215EA for ; Mon, 2 Sep 2019 09:05:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730814AbfIBJF1 (ORCPT ); Mon, 2 Sep 2019 05:05:27 -0400 Received: from mx2.suse.de ([195.135.220.15]:39448 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1730361AbfIBJF0 (ORCPT ); Mon, 2 Sep 2019 05:05:26 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id BA11FAC4A; Mon, 2 Sep 2019 09:05:25 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id C80201E406C; Mon, 2 Sep 2019 10:56:28 +0200 (CEST) Date: Mon, 2 Sep 2019 10:56:28 +0200 From: Jan Kara To: Tejun Heo Cc: Jens Axboe , Jan Kara , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com Subject: Re: [block/for-next] writeback: don't access page->mapping directly in track_foreign_dirty TP Message-ID: <20190902085628.GC14207@quack2.suse.cz> References: <20190830233954.GC2263813@devbig004.ftw2.facebook.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190830233954.GC2263813@devbig004.ftw2.facebook.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 30-08-19 16:39:54, Tejun Heo wrote: > page->mapping may encode different values in it and page_mapping() > should always be used to access the mapping pointer. > track_foreign_dirty tracepoint was incorrectly accessing page->mapping > directly. Use page_mapping() instead. Also, add NULL checks while at > it. > > Signed-off-by: Tejun Heo > Reported-by: Jan Kara > Fixes: 3a8e9ac89e6a ("writeback: add tracepoints for cgroup foreign writebacks") I can see Jens already picked this up so this is just informative: The patch now looks good to me. Honza > --- > include/trace/events/writeback.h | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/include/trace/events/writeback.h b/include/trace/events/writeback.h > index 3dc9fb9e7c78..3a27335fce2c 100644 > --- a/include/trace/events/writeback.h > +++ b/include/trace/events/writeback.h > @@ -251,9 +251,12 @@ TRACE_EVENT(track_foreign_dirty, > ), > > TP_fast_assign( > + struct address_space *mapping = page_mapping(page); > + struct inode *inode = mapping ? mapping->host : NULL; > + > strncpy(__entry->name, dev_name(wb->bdi->dev), 32); > __entry->bdi_id = wb->bdi->id; > - __entry->ino = page->mapping->host->i_ino; > + __entry->ino = inode ? inode->i_ino : 0; > __entry->memcg_id = wb->memcg_css->id; > __entry->cgroup_ino = __trace_wb_assign_cgroup(wb); > __entry->page_cgroup_ino = page->mem_cgroup->css.cgroup->kn->id.ino; -- Jan Kara SUSE Labs, CR