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

From: Ed Cashin
Date: Wed Aug 07 2013 - 19:27:48 EST

On Aug 7, 2013, at 5:26 PM, Andrew Morton wrote:

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

That BUG was added to the aoe driver in a commit that first appears in v3.7. It persists until this patch adds the code that handles the situation that the BUG was intended to detect.

[ecashin@marino linux]$ git describe --contains --match 'v*' 69cf2d85de773d998798e47e3335b85e5645d157
[ecashin@marino linux]$

Ed Cashin

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