From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934349AbcHDVsX (ORCPT ); Thu, 4 Aug 2016 17:48:23 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:51465 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932387AbcHDVsV (ORCPT ); Thu, 4 Aug 2016 17:48:21 -0400 Date: Thu, 4 Aug 2016 14:46:49 -0700 From: Andrew Morton To: Tetsuo Handa Cc: Geert Uytterhoeven , Michal Hocko , Oleg Nesterov , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH/RFC] mm, oom: Fix uninitialized ret in task_will_free_mem() Message-Id: <20160804144649.7ac4727ad0d93097c4055610@linux-foundation.org> In-Reply-To: <178c5e9b-b92d-b62b-40a9-ee98b10d6bce@I-love.SAKURA.ne.jp> References: <1470255599-24841-1-git-send-email-geert@linux-m68k.org> <178c5e9b-b92d-b62b-40a9-ee98b10d6bce@I-love.SAKURA.ne.jp> X-Mailer: Sylpheed 3.4.1 (GTK+ 2.24.23; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 4 Aug 2016 21:28:13 +0900 Tetsuo Handa wrote: > > > > Fixes: 1af8bb43269563e4 ("mm, oom: fortify task_will_free_mem()") > > Signed-off-by: Geert Uytterhoeven > > --- > > Untested. I'm not familiar with the code, hence the default value of > > true was deducted from the logic in the loop (return false as soon as > > __task_will_free_mem() has returned false). > > I think ret = true is correct. Andrew, please send to linux.git. task_will_free_mem() is too hard to understand. We're examining task "A": : for_each_process(p) { : if (!process_shares_mm(p, mm)) : continue; : if (same_thread_group(task, p)) : continue; So here, we've found a process `p' which shares A's mm and which does not share A's thread group. : ret = __task_will_free_mem(p); And here we check to see if killing `p' would free up memory. : if (!ret) : break; If killing `p' will not free memory then give up the scan of all processes because , and we decide that killing `A' will not free memory either, because some other task is holding onto A's memory anyway. : } And if no task is found to be sharing A's mm while not sharing A's thread group then fall through and decide to kill A. In which case the patch to return `true' is correct. Correctish? Maybe. Can we please get some comments in there to demystify the decision-making?