linux-kernel - RE: [PATCH 2.6.23-rc7 0/3] async_tx and md-accel fixes for 2.6.23

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Message-ID: <0C7297FA1D2D244A9C7F6959C0BF1E52027D909B@azsmsx413.amr.corp.intel.com>
Date:	Fri, 21 Sep 2007 13:52:24 -0700
From:	"Williams, Dan J" <dan.j.williams@...el.com>
To:	"Andrew Morton" <akpm@...ux-foundation.org>
Cc:	<linux-kernel@...r.kernel.org>, <linux-raid@...r.kernel.org>,
	<neilb@...e.de>, <yur@...raft.com>, <saeed.bishara@...il.com>,
	"Nelson, Shannon" <shannon.nelson@...el.com>
Subject: RE: [PATCH 2.6.23-rc7 0/3] async_tx and md-accel fixes for 2.6.23

> From: Andrew Morton [mailto:akpm@...ux-foundation.org]
> > Fix a couple bugs and provide documentation for the async_tx api.
> >
> > Neil, please 'ack' patch #3.
> >
> > git://lost.foo-projects.org/~dwillia2/git/iop
async-tx-fixes-for-linus
> 
> Well it looks like Neil is on vacation or is hiding from us or
something.
> 
> In which case our options would be to go ahead and merge your #3 with
> our fingers crossed, or wait and do it in 2.6.23.1 or .2.
> 
> How serious is this bug which you're fixing?  Will it affect users
> of "legacy" MD setups, or only those who have enabled fancy dma-engine
> features?
> 
The symptom is raid array that fails to complete a read request.

It has only been triggered by Yuri when he tried a dma-engine
configuration on his PPC platform with PAGE_SIZE=64K, this opens a large
window for the bug to hit.  The window is much smaller but not 100%
closed in the !dma-engine case, although no one else has hit it. 

2.6.22 returned reads from handle_stripe under the stripe lock so this
patch can be seen as 'reverting a botched micro-optimization' versus
'introducing a new way to handle reads'.

> Either way, we need to get #2 (at least) in to Linus.

#2 is less critical and cannot hit with any of the current drivers in
the kernel, so it is ok if this one misses 2.6.23.
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