From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf0-f71.google.com (mail-lf0-f71.google.com [209.85.215.71]) by kanga.kvack.org (Postfix) with ESMTP id D9E0A6B0253 for ; Mon, 30 May 2016 02:43:05 -0400 (EDT) Received: by mail-lf0-f71.google.com with SMTP id o70so86104665lfg.1 for ; Sun, 29 May 2016 23:43:05 -0700 (PDT) Received: from mail-wm0-f65.google.com (mail-wm0-f65.google.com. [74.125.82.65]) by mx.google.com with ESMTPS id v132si29104424wme.82.2016.05.29.23.43.04 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 29 May 2016 23:43:04 -0700 (PDT) Received: by mail-wm0-f65.google.com with SMTP id a136so19488921wme.0 for ; Sun, 29 May 2016 23:43:04 -0700 (PDT) Date: Mon, 30 May 2016 08:43:02 +0200 From: Michal Hocko Subject: Re: [PATCH] oom_reaper: don't call mmput_async() on uninitialized mm Message-ID: <20160530064302.GA22928@dhcp22.suse.cz> References: <1464336081-994232-1-git-send-email-arnd@arndb.de> <20160527081059.GE27686@dhcp22.suse.cz> <20160527125534.b8be57b284599f5424512d09@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160527125534.b8be57b284599f5424512d09@linux-foundation.org> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Arnd Bergmann , David Rientjes , Tetsuo Handa , Johannes Weiner , Oleg Nesterov , linux-mm@kvack.org, linux-kernel@vger.kernel.org On Fri 27-05-16 12:55:34, Andrew Morton wrote: > 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.. looks good to me as well. Thanks! > --- 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; > } > > _ -- Michal Hocko SUSE Labs -- 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