From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io0-f199.google.com (mail-io0-f199.google.com [209.85.223.199]) by kanga.kvack.org (Postfix) with ESMTP id DA2E26B0253 for ; Mon, 30 May 2016 09:49:23 -0400 (EDT) Received: by mail-io0-f199.google.com with SMTP id p194so37766729iod.2 for ; Mon, 30 May 2016 06:49:23 -0700 (PDT) Received: from EUR01-DB5-obe.outbound.protection.outlook.com (mail-db5eur01on0124.outbound.protection.outlook.com. [104.47.2.124]) by mx.google.com with ESMTPS id t17si11340979otd.30.2016.05.30.06.49.22 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Mon, 30 May 2016 06:49:23 -0700 (PDT) Date: Mon, 30 May 2016 16:49:15 +0300 From: Vladimir Davydov Subject: Re: [PATCH 1/6] proc, oom: drop bogus task_lock and mm check Message-ID: <20160530134915.GD8293@esperanza> 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 , Oleg Nesterov , Andrew Morton , LKML , Michal Hocko On Mon, May 30, 2016 at 03:05:51PM +0200, Michal Hocko wrote: > From: Michal Hocko > > 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. > > Signed-off-by: Michal Hocko Reviewed-by: Vladimir Davydov -- 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