linux-kernel - Re: msync(2) bug(?), returns AOP_WRITEPAGE

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Date:	Mon, 15 Oct 2007 14:47:52 +0300
From:	"Pekka Enberg" <penberg@...helsinki.fi>
To:	"Erez Zadok" <ezk@...sunysb.edu>
Cc:	"Hugh Dickins" <hugh@...itas.com>, "Ryan Finnie" <ryan@...nie.org>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	cjwatson@...ntu.com, linux-mm@...ck.org
Subject: Re: msync(2) bug(?), returns AOP_WRITEPAGE_ACTIVATE to userland

Hi,

On 10/15/07, Erez Zadok <ezk@...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
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