From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner+w=401wt.eu-S1754742AbYKXU53@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1754742AbYKXU53 (ORCPT <rfc822;w@1wt.eu>);
	Mon, 24 Nov 2008 15:57:29 -0500
Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754133AbYKXUzY
	(ORCPT <rfc822;linux-kernel-outgoing>);
	Mon, 24 Nov 2008 15:55:24 -0500
Received: from wf-out-1314.google.com ([209.85.200.172]:54406 "EHLO
	wf-out-1314.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1754154AbYKXUzV (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Mon, 24 Nov 2008 15:55:21 -0500
DomainKey-Signature: a=rsa-sha1; c=nofws;
        d=gmail.com; s=gamma;
        h=message-id:date:from:sender:to:subject:cc:in-reply-to:mime-version
         :content-type:content-transfer-encoding:content-disposition
         :references:x-google-sender-auth;
        b=H1WZ8TfhNk96RfahBYPJUw/fvVRUQsQoWjdL4ISFX6UOb5Sc0MevBVm2W9++fGvTv5
         EJkIEFUsZONowCxMFDKEfuIN25NgfVkek/rmplljpEV8T913W9/7b4xzcTWrPTWNZ8BO
         JyZL5XPYDfM2BFYg+mdnsr7Wg70Kwt/q7O3/8=
Message-ID: <84144f020811241255v2d4de38j59ceeb967227489@mail.gmail.com>
Date: Mon, 24 Nov 2008 22:55:20 +0200
From: "Pekka Enberg" <penberg@cs.helsinki.fi>
To: "Paul Menage" <menage@google.com>
Subject: Re: [PATCH][V3]Make get_user_pages interruptible
Cc: "Ying Han" <yinghan@google.com>, linux-mm@kvack.org,
       linux-kernel@vger.kernel.org, akpm <akpm@linux-foundation.org>,
       "David Rientjes" <rientjes@google.com>,
       "Rohit Seth" <rohitseth@google.com>
In-Reply-To: <6599ad830811241202o74312a18m84ed86a5f4393086@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Content-Disposition: inline
References: <604427e00811211731l40898486r1a58e4940f3859e9@mail.gmail.com>
	 <6599ad830811241202o74312a18m84ed86a5f4393086@mail.gmail.com>
X-Google-Sender-Auth: 1e8da49ca58f4703
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

Hi Paul,

On Fri, Nov 21, 2008 at 5:31 PM, Ying Han <yinghan@google.com> wrote:
>>                         */
>> -                       if (unlikely(test_tsk_thread_flag(tsk, TIF_MEMDIE)))
>> -                               return i ? i : -ENOMEM;
>> +                       if (unlikely(sigkill_pending(tsk)))
>> +                               return i ? i : -ERESTARTSYS;

On Mon, Nov 24, 2008 at 10:02 PM, Paul Menage <menage@google.com> wrote:
> You've changed the check from sigkill_pending(current) to sigkill_pending(tsk).
>
> I originally made that sigkill_pending(current) since we want to avoid
> tasks entering an unkillable state just because they're doing
> get_user_pages() on a system that's short of memory. Admittedly for
> the main case that we care about, mlock() (or an mmap() with
> MCL_FUTURE set) then tsk==current, but philosophically it seems to me
> to be more correct to do the check against current than tsk, since
> current is the thing that's actually allocating the memory. But maybe
> it would be better to check both?

Well, most callers seem to pass 'current' to get_user_pages() but for
the out-of-tree revoke patches, for example, you certainly want to
check sigkill_pending(current) as well; otherwise the revoke operation
is unkillable while in get_user_pages().

Not that revoke() is going to hit mainline any time soon but it does
serve as an argument for checking both.

                        Pekka