From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Kohli, Gaurav" Subject: Re: [PATCH] mm: oom: Fix race condition between oom_badness and do_exit of task Date: Thu, 8 Mar 2018 10:21:26 +0530 Message-ID: <22ebd655-ece4-37e5-5a98-e9750cb20665@codeaurora.org> References: <1520427454-22813-1-git-send-email-gkohli@codeaurora.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: David Rientjes 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 List-Id: linux-arm-msm@vger.kernel.org On 3/8/2018 2:26 AM, David Rientjes wrote: > On Wed, 7 Mar 2018, Gaurav Kohli wrote: > >> diff --git a/mm/oom_kill.c b/mm/oom_kill.c >> index 6fd9773..5f4cc4b 100644 >> --- a/mm/oom_kill.c >> +++ b/mm/oom_kill.c >> @@ -114,9 +114,11 @@ struct task_struct *find_lock_task_mm(struct task_struct *p) >> >> for_each_thread(p, t) { >> task_lock(t); >> + get_task_struct(t); >> if (likely(t->mm)) >> goto found; >> task_unlock(t); >> + put_task_struct(t); >> } >> t = NULL; >> found: > We hold rcu_read_lock() here, so perhaps only do get_task_struct() before > doing rcu_read_unlock() and we have a non-NULL t? Here rcu_read_lock will not help, as our task may change due to below algo: for_each_thread(p, t) { task_lock(t); + get_task_struct(t); if (likely(t->mm)) goto found; task_unlock(t); + put_task_struct(t) So only we can increase usage counter here only at the current task. I have seen you new patch, that seems valid to me and it will resolve our issue. Thanks for support. Regards Gaurav > -- Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.