From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Pekka Enberg" <penberg@cs.helsinki.fi>
Subject: Re: msync(2) bug(?), returns AOP_WRITEPAGE_ACTIVATE to userland
Date: Mon, 15 Oct 2007 14:47:52 +0300
Message-ID: <84144f020710150447o94b1babo8b6e6a647828465f@mail.gmail.com>
References: <Pine.LNX.4.64.0710142049000.13119@sbz-30.cs.Helsinki.FI>
	 <200710142232.l9EMW8kK029572@agora.fsl.cs.sunysb.edu>
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Cc: "Hugh Dickins" <hugh@veritas.com>, "Ryan Finnie" <ryan@finnie.org>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	cjwatson@ubuntu.com, linux-mm@kvack.org
To: "Erez Zadok" <ezk@cs.sunysb.edu>
Return-path: <linux-kernel-owner+glk-linux-kernel-3=40m.gmane.org-S1764720AbXJOLsL@vger.kernel.org>
In-Reply-To: <200710142232.l9EMW8kK029572@agora.fsl.cs.sunysb.edu>
Content-Disposition: inline
Sender: linux-kernel-owner@vger.kernel.org
List-Id: linux-fsdevel.vger.kernel.org

Hi,

On 10/15/07, Erez Zadok <ezk@cs.sunysb.edu> wrote:
> Pekka, with a small change to your patch (to handle time-based cache
> coherency), your patch worked well and passed all my tests.  Thanks.
>
> So now I wonder if we still need the patch to prevent AOP_WRITEPAGE_ACTIVATE
> from being returned to userland.  I guess we still need it, b/c even with
> your patch, generic_writepages() can return AOP_WRITEPAGE_ACTIVATE back to
> the VFS and we need to ensure that doesn't "leak" outside the kernel.

I wonder whether _not setting_ BDI_CAP_NO_WRITEBACK implies that
->writepage() will never return AOP_WRITEPAGE_ACTIVATE for
!wbc->for_reclaim case which would explain why we haven't hit this bug
before. Hugh, Andrew?

And btw, I think we need to fix ecryptfs too.

                                           Pekka