linux-kernel - Re: PATCH 2.6.21-rc1 aoe: handle zero

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Message-Id: <20070301210942.ebf40993.akpm@linux-foundation.org>
Date:	Thu, 1 Mar 2007 21:09:42 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	support@...aid.com, "Ed L. Cashin" <ecashin@...aid.com>,
	linux-kernel@...r.kernel.org, Greg KH <greg@...ah.com>
Subject: Re: PATCH 2.6.21-rc1 aoe: handle zero _count pages in bios

On Fri, 2 Mar 2007 05:03:51 +0000 Christoph Hellwig <hch@...radead.org> wrote:

> On Thu, Mar 01, 2007 at 09:00:44PM -0800, Andrew Morton wrote:
> > I that case we're talking about different things.
> > 
> > I thought the proposal was to continue to use slab pages, but to take a ref
> > on them as they're added to the bio, drop that ref in bi_end_io()?
> 
> That would give you silent memory corruption in case the networking code
> hold a reference after the memory gets returned to slab and reused.

Well, given that bi_end_io() is called after the "io" has completed, I'm
assuming that networking has completely finished with the memory by the
time bi_end_io() gets called.

I guess one can envisage situations where that might not happen, but they'd
be terribly buggy ones, surely.

> We need to either stop allowing to pass slab memory to the block layer,
> or document that drivers need to handle it specially and give them a
> way to find out about them. (Or do the horrible slab refcounting hack
> I wrote up above)

OK.  So you're proposing that XFS and ext3 simply stop sing slab for this
memory?

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