Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751456AbdI1Upd (ORCPT ); Thu, 28 Sep 2017 16:45:33 -0400 Received: from www262.sakura.ne.jp ([202.181.97.72]:42495 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750821AbdI1Upc (ORCPT ); Thu, 28 Sep 2017 16:45:32 -0400 To: yang.s@alibaba-inc.com, mhocko@kernel.org Cc: cl@linux.com, penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 0/2 v8] oom: capture unreclaimable slab info in oom message From: Tetsuo Handa References: <1506548776-67535-1-git-send-email-yang.s@alibaba-inc.com> <7e8684c2-c9e8-f76a-d7fb-7d5bf7682321@alibaba-inc.com> <201709290457.CAC30283.VFtMFOFOJLQHOS@I-love.SAKURA.ne.jp> <69a33b7a-afdf-d798-2e03-0c92dd94bfa6@alibaba-inc.com> In-Reply-To: <69a33b7a-afdf-d798-2e03-0c92dd94bfa6@alibaba-inc.com> Message-Id: <201709290545.HGH30269.LOVtSHFQOFJFOM@I-love.SAKURA.ne.jp> X-Mailer: Winbiff [Version 2.51 PL2] X-Accept-Language: ja,en,zh Date: Fri, 29 Sep 2017 05:45:31 +0900 Mime-Version: 1.0 Content-Type: text/plain; charset=iso-2022-jp Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2128 Lines: 43 Yang Shi wrote: > On 9/28/17 12:57 PM, Tetsuo Handa wrote: > > Yang Shi wrote: > >> On 9/27/17 9:36 PM, Tetsuo Handa wrote: > >>> On 2017/09/28 6:46, Yang Shi wrote: > >>>> Changelog v7 -> v8: > >>>> * Adopted Michal’s suggestion to dump unreclaim slab info when unreclaimable slabs amount > total user memory. Not only in oom panic path. > >>> > >>> Holding slab_mutex inside dump_unreclaimable_slab() was refrained since V2 > >>> because there are > >>> > >>> mutex_lock(&slab_mutex); > >>> kmalloc(GFP_KERNEL); > >>> mutex_unlock(&slab_mutex); > >>> > >>> users. If we call dump_unreclaimable_slab() for non OOM panic path, aren't we > >>> introducing a risk of crash (i.e. kernel panic) for regular OOM path? > >> > >> I don't see the difference between regular oom path and oom path other > >> than calling panic() at last. > >> > >> And, the slab dump may be called by panic path too, it is for both > >> regular and panic path. > > > > Calling a function that might cause kerneloops immediately before calling panic() > > would be tolerable, for the kernel will panic after all. But calling a function > > that might cause kerneloops when there is no plan to call panic() is a bug. > > I got your point. slab_mutex is used to protect the list of all the > slabs, since we are already in oom, there should be not kmem cache > destroy happen during the list traverse. And, list_for_each_entry() has > been replaced to list_for_each_entry_safe() to make the traverse more > robust. I consider that OOM event and kmem chache destroy event can run concurrently because slab_mutex is not held by OOM event (and unfortunately cannot be held due to possibility of deadlock) in order to protect the list of all the slabs. I don't think replacing list_for_each_entry() with list_for_each_entry_safe() makes the traverse more robust, for list_for_each_entry_safe() does not defer freeing of memory used by list element. Rather, replacing list_for_each_entry() with list_for_each_entry_rcu() (and making relevant changes such as rcu_read_lock()/rcu_read_unlock()/synchronize_rcu()) will make the traverse safe.