From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933911AbeEJDJi (ORCPT ); Wed, 9 May 2018 23:09:38 -0400 Received: from out02.mta.xmission.com ([166.70.13.232]:59323 "EHLO out02.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756584AbeEJDJe (ORCPT ); Wed, 9 May 2018 23:09:34 -0400 From: ebiederm@xmission.com (Eric W. Biederman) To: Oleg Nesterov 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 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> <20180509144016.GA25742@redhat.com> Date: Wed, 09 May 2018 22:09:25 -0500 In-Reply-To: <20180509144016.GA25742@redhat.com> (Oleg Nesterov's message of "Wed, 9 May 2018 16:40:16 +0200") Message-ID: <87vabwp5p6.fsf@xmission.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-SPF: eid=1fGbxT-0007JS-0y;;;mid=<87vabwp5p6.fsf@xmission.com>;;;hst=in02.mta.xmission.com;;;ip=97.90.247.198;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX1/9y98JOJXTymzqFuqsmdGX3vLJuwRupnM= X-SA-Exim-Connect-IP: 97.90.247.198 X-SA-Exim-Mail-From: ebiederm@xmission.com X-Spam-Report: * -1.0 ALL_TRUSTED Passed through trusted hosts only via SMTP * 0.0 T_TM2_M_HEADER_IN_MSG BODY: No description available. * 0.8 BAYES_50 BODY: Bayes spam probability is 40 to 60% * [score: 0.5000] * -0.0 DCC_CHECK_NEGATIVE Not listed in DCC * [sa07 1397; Body=1 Fuz1=1 Fuz2=1] * 0.1 XMSolicitRefs_0 Weightloss drug * 0.0 T_TooManySym_01 4+ unique symbols in subject X-Spam-DCC: XMission; sa07 1397; Body=1 Fuz1=1 Fuz2=1 X-Spam-Combo: ;Oleg Nesterov X-Spam-Relay-Country: X-Spam-Timing: total 1275 ms - load_scoreonly_sql: 0.06 (0.0%), signal_user_changed: 2.8 (0.2%), b_tie_ro: 1.87 (0.1%), parse: 0.86 (0.1%), extract_message_metadata: 3.3 (0.3%), get_uri_detail_list: 1.59 (0.1%), tests_pri_-1000: 4.2 (0.3%), tests_pri_-950: 1.24 (0.1%), tests_pri_-900: 1.04 (0.1%), tests_pri_-400: 27 (2.1%), check_bayes: 25 (2.0%), b_tokenize: 8 (0.6%), b_tok_get_all: 7 (0.6%), b_comp_prob: 2.3 (0.2%), b_tok_touch_all: 4.5 (0.4%), b_finish: 1.99 (0.2%), tests_pri_0: 1222 (95.8%), check_dkim_signature: 0.55 (0.0%), check_dkim_adsp: 2.9 (0.2%), tests_pri_500: 4.9 (0.4%), rewrite_mail: 0.00 (0.0%) Subject: Re: [PATCH] memcg: Replace mm->owner with mm->memcg X-Spam-Flag: No X-SA-Exim-Version: 4.2.1 (built Thu, 05 May 2016 13:38:54 -0600) X-SA-Exim-Scanned: Yes (on in02.mta.xmission.com) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Oleg Nesterov writes: > 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? Sort of. I don't know how the memcg gets away without migrating charges when it migrates a process. With charges not being migrated I don't think this is observable. That does look like a real issue however. >> > 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. Eric