From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f71.google.com (mail-oi0-f71.google.com [209.85.218.71]) by kanga.kvack.org (Postfix) with ESMTP id 847286B0253 for ; Mon, 30 May 2016 13:43:29 -0400 (EDT) Received: by mail-oi0-f71.google.com with SMTP id a143so279480636oii.2 for ; Mon, 30 May 2016 10:43:29 -0700 (PDT) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id 186si26879758ith.8.2016.05.30.10.43.28 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 30 May 2016 10:43:28 -0700 (PDT) Date: Mon, 30 May 2016 19:43:24 +0200 From: Oleg Nesterov Subject: Re: [PATCH 1/6] proc, oom: drop bogus task_lock and mm check Message-ID: <20160530174324.GA25382@redhat.com> References: <1464613556-16708-1-git-send-email-mhocko@kernel.org> <1464613556-16708-2-git-send-email-mhocko@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1464613556-16708-2-git-send-email-mhocko@kernel.org> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: linux-mm@kvack.org, Tetsuo Handa , David Rientjes , Vladimir Davydov , Andrew Morton , LKML , Michal Hocko On 05/30, Michal Hocko wrote: > > both oom_adj_write and oom_score_adj_write are using task_lock, > check for task->mm and fail if it is NULL. This is not needed because > the oom_score_adj is per signal struct so we do not need mm at all. > The code has been introduced by 3d5992d2ac7d ("oom: add per-mm oom > disable count") but we do not do per-mm oom disable since c9f01245b6a7 > ("oom: remove oom_disable_count"). > > The task->mm check is even not correct because the current thread might > have exited but the thread group might be still alive - e.g. thread > group leader would lead that echo $VAL > /proc/pid/oom_score_adj would > always fail with EINVAL while /proc/pid/task/$other_tid/oom_score_adj > would succeed. This is unexpected at best. > > Remove the lock along with the check to fix the unexpected behavior > and also because there is not real need for the lock in the first place. ACK and we should also remove lock_task_sighand(). as for oom_adj_read() and oom_score_adj_read() we can just remove it right now; it was previously needed to ensure the task->signal != NULL, today this is always true. Oleg. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org