From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935173AbeEIOkX (ORCPT ); Wed, 9 May 2018 10:40:23 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:39996 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S933988AbeEIOkV (ORCPT ); Wed, 9 May 2018 10:40:21 -0400 Date: Wed, 9 May 2018 16:40:16 +0200 From: Oleg Nesterov To: "Eric W. Biederman" Cc: Johannes Weiner , Michal Hocko , Kirill Tkhai , akpm@linux-foundation.org, peterz@infradead.org, viro@zeniv.linux.org.uk, mingo@kernel.org, paulmck@linux.vnet.ibm.com, keescook@chromium.org, riel@redhat.com, tglx@linutronix.de, kirill.shutemov@linux.intel.com, marcos.souza.org@gmail.com, hoeun.ryu@gmail.com, pasha.tatashin@oracle.com, gs051095@gmail.com, dhowells@redhat.com, rppt@linux.vnet.ibm.com, linux-kernel@vger.kernel.org, Balbir Singh , Tejun Heo Subject: Re: [PATCH] memcg: Replace mm->owner with mm->memcg Message-ID: <20180509144016.GA25742@redhat.com> References: <20180503133338.GA23401@redhat.com> <87y3h0x0qg.fsf@xmission.com> <20180504142056.GA26151@redhat.com> <87r2mrh4is.fsf@xmission.com> <20180504145435.GA26573@redhat.com> <87y3gzfmjt.fsf@xmission.com> <20180504162209.GB26573@redhat.com> <871serfk77.fsf@xmission.com> <20180507143358.GA3071@redhat.com> <87vabyvnw0.fsf@xmission.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87vabyvnw0.fsf@xmission.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/07, Eric W. Biederman wrote: > > Oleg Nesterov writes: > > > before your patch get_mem_cgroup_from_mm() looks at mm->owner == current > > (in this case) and mem_cgroup_from_task() should return the correct memcg > > even if execing task migrates after bprm_mm_init(). At least in the common > > case when the old mm is not shared. > > > > After your patch the memory allocations in copy_strings() won't be accounted > > correctly, bprm->mm->memcg is wrong if this task migrates. And iiuc your recent > > "[PATCH 2/2] memcg: Close the race between migration and installing bprm->mm as mm" > > doesn't fix the problem. > > > > No? > > The patch does solve the issue. There should be nothing a userspace > process can observe that should tell it where in the middle of exec > such a migration happend so placing the migration at what from the > kernel's perspective might be technically later should not be a problem. > > If it is a problem the issue is that there is a way to observe the > difference. So. The task migrates from some MEMCG right after bprm_mm_init(). copy_strings() triggers OOM in MEMCG. This is quite possible, it can use a lot of memory and that is why we have acct_arg_size() to make these allocations visible to oom killer. task_in_mem_cgroup(MEMCG) returns false and oom killer has to kill another innocent process in MEMCG. Does this look like a way to observe the difference? > > Perhaps we can change get_mem_cgroup_from_mm() to use > > mem_cgroup_from_css(current, memory_cgrp_id) if mm->memcg == NULL? > > Please God no. Having any unnecessary special case is just going to > confuse people and cause bugs. To me the unnecessary special case is the new_mm->memcg which is used for accounting but doesn't follow migration till exec_mmap(). But I won't argue. Oleg.