From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl0-f70.google.com (mail-pl0-f70.google.com [209.85.160.70]) by kanga.kvack.org (Postfix) with ESMTP id EB5856B0005 for ; Fri, 9 Mar 2018 07:04:46 -0500 (EST) Received: by mail-pl0-f70.google.com with SMTP id t12-v6so4431821plo.9 for ; Fri, 09 Mar 2018 04:04:46 -0800 (PST) Received: from smtp.codeaurora.org (smtp.codeaurora.org. [198.145.29.96]) by mx.google.com with ESMTPS id h10si654345pgf.326.2018.03.09.04.04.44 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 09 Mar 2018 04:04:44 -0800 (PST) Subject: Re: [PATCH] mm: oom: Fix race condition between oom_badness and do_exit of task References: <1520427454-22813-1-git-send-email-gkohli@codeaurora.org> <22ebd655-ece4-37e5-5a98-e9750cb20665@codeaurora.org> <14ba6c44-d444-bd0a-0bac-0c6851b19344@codeaurora.org> <201803091948.FBC21396.LHOMSFFOVFtQJO@I-love.SAKURA.ne.jp> From: "Kohli, Gaurav" Message-ID: Date: Fri, 9 Mar 2018 17:34:39 +0530 MIME-Version: 1.0 In-Reply-To: <201803091948.FBC21396.LHOMSFFOVFtQJO@I-love.SAKURA.ne.jp> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: owner-linux-mm@kvack.org List-ID: To: Tetsuo Handa , rientjes@google.com Cc: akpm@linux-foundation.org, mhocko@suse.com, kirill.shutemov@linux.intel.com, aarcange@redhat.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org On 3/9/2018 4:18 PM, Tetsuo Handa wrote: > Kohli, Gaurav wrote: >>> t->alloc_lock is still held when leaving find_lock_task_mm(), which means >>> that t->mm != NULL. But nothing prevents t from setting t->mm = NULL at >>> exit_mm() from do_exit() and calling exit_creds() from __put_task_struct(t) >>> after task_unlock(t) is called. Seems difficult to trigger race window. Maybe >>> something has preempted because oom_badness() becomes outside of RCU grace >>> period upon leaving find_lock_task_mm() when called from proc_oom_score(). >> Hi Tetsuo, >> >> Yes it is not easy to reproduce seen twice till now and i agree with >> your analysis. But David has already fixing this in different way, >> So that also looks better to me: >> >> https://patchwork.kernel.org/patch/10265641/ >> > Yes, I'm aware of that patch. > >> But if need to keep that code, So we have to bump up the task >> reference that's only i can think of now. > I don't think so, for I think it is safe to call > has_capability_noaudit(p) with p->alloc_lock held. > > diff --git a/mm/oom_kill.c b/mm/oom_kill.c > index f2e7dfb..4efcfb8 100644 > --- a/mm/oom_kill.c > +++ b/mm/oom_kill.c > @@ -222,7 +222,6 @@ unsigned long oom_badness(struct task_struct *p, struct mem_cgroup *memcg, > */ > points = get_mm_rss(p->mm) + get_mm_counter(p->mm, MM_SWAPENTS) + > mm_pgtables_bytes(p->mm) / PAGE_SIZE; > - task_unlock(p); > > /* > * Root processes get 3% bonus, just like the __vm_enough_memory() > @@ -230,6 +229,7 @@ unsigned long oom_badness(struct task_struct *p, struct mem_cgroup *memcg, > */ > if (has_capability_noaudit(p, CAP_SYS_ADMIN)) > points -= (points * 3) / 100; > + task_unlock(p); Earlier i have thought the same to post this, but this may create problem if there are sleeping calls in has_capability_noaudit ? > > /* Normalize to oom_score_adj units */ > adj *= totalpages / 1000; > -- Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.