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=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 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 A299DC3A5A6 for ; Fri, 30 Aug 2019 15:40:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7940023427 for ; Fri, 30 Aug 2019 15:40:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728271AbfH3PkZ (ORCPT ); Fri, 30 Aug 2019 11:40:25 -0400 Received: from mx2.suse.de ([195.135.220.15]:45286 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727434AbfH3PkZ (ORCPT ); Fri, 30 Aug 2019 11:40:25 -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 2D789AEF5; Fri, 30 Aug 2019 15:40:24 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id B91411E43A8; Fri, 30 Aug 2019 17:40:23 +0200 (CEST) Date: Fri, 30 Aug 2019 17:40:23 +0200 From: Jan Kara To: Tejun Heo Cc: Jens Axboe , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, Jan Kara Subject: Re: [PATCH block/for-next] writeback: add tracepoints for cgroup foreign writebacks Message-ID: <20190830154023.GC25069@quack2.suse.cz> References: <20190829224701.GX2263813@devbig004.ftw2.facebook.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190829224701.GX2263813@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 Thu 29-08-19 15:47:19, Tejun Heo wrote: > cgroup foreign inode handling has quite a bit of heuristics and > internal states which sometimes makes it difficult to understand > what's going on. Add tracepoints to improve visibility. > > Signed-off-by: Tejun Heo ... > +TRACE_EVENT(track_foreign_dirty, > + > + TP_PROTO(struct page *page, struct bdi_writeback *wb), > + > + TP_ARGS(page, wb), > + > + TP_STRUCT__entry( > + __array(char, name, 32) > + __field(u64, bdi_id) > + __field(unsigned long, ino) > + __field(unsigned int, memcg_id) > + __field(unsigned int, cgroup_ino) > + __field(unsigned int, page_cgroup_ino) > + ), > + > + TP_fast_assign( > + strncpy(__entry->name, dev_name(wb->bdi->dev), 32); > + __entry->bdi_id = wb->bdi->id; > + __entry->ino = page->mapping->host->i_ino; > + __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; > + ), 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? Honza -- Jan Kara SUSE Labs, CR