linux-kernel - Re: [PATCH] connector: improved unaligned access error fix

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Message-Id: <20131114.172023.1565829138219271745.davem@davemloft.net>
Date:	Thu, 14 Nov 2013 17:20:23 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	cmetcalf@...era.com
Cc:	zbr@...emap.net, erikj@....com, akpm@...l.org, matthltc@...ibm.com,
	zaitcev@...hat.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] connector: improved unaligned access error fix

From: Chris Metcalf <cmetcalf@...era.com>
Date: Thu, 14 Nov 2013 12:09:21 -0500

> In af3e095a1fb4, Erik Jacobsen fixed one type of unaligned access
> bug for ia64 by converting a 64-bit write to use put_unaligned().
> Unfortunately, since gcc will convert a short memset() to a series
> of appropriately-aligned stores, the problem is now visible again
> on tilegx, where the memset that zeros out proc_event is converted
> to three 64-bit stores, causing an unaligned access panic.
> 
> A better fix for the original problem is to ensure that proc_event
> is aligned to 8 bytes here.  We can do that relatively easily by
> arranging to start the struct cn_msg aligned to 8 bytes and then
> offset by 4 bytes.  Doing so means that the immediately following
> proc_event structure is then correctly aligned to 8 bytes.
> 
> The result is that the memset() stores are now aligned, and as an
> added benefit, we can remove the put_unaligned() calls in the code.
> 
> Signed-off-by: Chris Metcalf <cmetcalf@...era.com>

This looks fine to me, applied and queued up for -stable, thanks
Chris.
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