Re: [PATCH] aoe: adjust ref of head for compound page tails

From: Andrew Morton
Date: Wed Aug 07 2013 - 17:26:53 EST

On Wed, 7 Aug 2013 17:21:32 -0400 Ed Cashin <ecashin@xxxxxxxxxx> wrote:

> > What are the end-user-visible effects of the problem which is being
> > fixed? Please always include this info when fixing bugs so that others
> > can work out what kernel version(s) need the patch.
> Sorry. I tried to cover that but maybe should have separated it more clearly from the running text.
> The patch changes the current behavior encountered with direct I/O and aoe:
> aoe can BUG when direct I/O used
> ... to a new behavior:
> aoe does not BUG when direct I/O is used
> And the user will never know that instead aoe is manipulating the _count of the head page, even though that's what's happening with this patch applied.
> (The user-visible effects that motivated the older patch that added the BUG to aoe when page tails are used for block I/O was a VM_BUG_ON that occurred when the aoe driver manipulated the _count of a compound page tail.)

OK, I added "Fix a BUG which can trigger when direct-IO is used with
AOE". Which kernel versions are affected?

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