From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755751AbcE0Tzh (ORCPT ); Fri, 27 May 2016 15:55:37 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:43867 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753205AbcE0Tzg (ORCPT ); Fri, 27 May 2016 15:55:36 -0400 Date: Fri, 27 May 2016 12:55:34 -0700 From: Andrew Morton To: Michal Hocko Cc: Arnd Bergmann , David Rientjes , Tetsuo Handa , Johannes Weiner , Oleg Nesterov , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] oom_reaper: don't call mmput_async() on uninitialized mm Message-Id: <20160527125534.b8be57b284599f5424512d09@linux-foundation.org> In-Reply-To: <20160527081059.GE27686@dhcp22.suse.cz> References: <1464336081-994232-1-git-send-email-arnd@arndb.de> <20160527081059.GE27686@dhcp22.suse.cz> 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 Fri, 27 May 2016 10:10:59 +0200 Michal Hocko wrote: > On Fri 27-05-16 10:00:48, Arnd Bergmann wrote: > > The change to the oom_reaper to hold a mutex inside __oom_reap_task() > > accidentally started calling mmput_async() on the local > > mm before that variable got initialized, as reported by gcc > > in linux-next: > > > > mm/oom_kill.c: In function '__oom_reap_task': > > mm/oom_kill.c:537:2: error: 'mm' may be used uninitialized in this function [-Werror=maybe-uninitialized] > > > > This rearranges the code slightly back to the state before patch > > but leaves the lock in place. The error handling in the function > > still looks a bit confusing and could probably be improved > > but I could not come up with a solution that made me happy > > for now. > > > > Signed-off-by: Arnd Bergmann > > Fixes: mmotm ("oom_reaper: close race with exiting task") > > Thanks for catching that Arnd? > > Acked-by: Michal Hocko I think I preferred my version - all those unwinding return statements can cause problems.. --- a/mm/oom_kill.c~oom_reaper-close-race-with-exiting-task-fix +++ a/mm/oom_kill.c @@ -443,7 +443,7 @@ static bool __oom_reap_task(struct task_ { struct mmu_gather tlb; struct vm_area_struct *vma; - struct mm_struct *mm; + struct mm_struct *mm = NULL; struct task_struct *p; struct zap_details details = {.check_swap_entries = true, .ignore_dirty = true}; @@ -534,7 +534,8 @@ unlock_oom: * different context because we shouldn't risk we get stuck there and * put the oom_reaper out of the way. */ - mmput_async(mm); + if (mm) + mmput_async(mm); return ret; } _