netdev - Re: alignment faults in 3.6

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Message-ID: <20121012090321.GA21164@n2100.arm.linux.org.uk>
Date:	Fri, 12 Oct 2012 10:03:21 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linux-arm-kernel@...ts.infradead.org,
	Måns Rullgård <mans@...sr.com>,
	David Laight <David.Laight@...lab.com>,
	Eric Dumazet <eric.dumazet@...il.com>, netdev@...r.kernel.org,
	Jon Masters <jonathan@...masters.org>
Subject: Re: alignment faults in 3.6

On Fri, Oct 12, 2012 at 08:11:42AM +0000, Arnd Bergmann wrote:
> On Thursday 11 October 2012, Måns Rullgård wrote:
> > > But, the IP header is expected to be aligned.
> > 
> > Everything tells the compiler the struct is perfectly aligned.  When the
> > buggy driver passes a misaligned pointer, bad things happen.
> 
> Would it be appropriate to add a WARN_ON_ONCE() in the alignment fault path
> then? If all alignment faults in the kernel are caused by broken drivers,
> that would at least give us some hope of finding those drivers while at the
> same time not causing much overhead in the case where we need to do the
> fixup in the meantime.

No.  It is my understanding that various IP option processing can also
cause the alignment fault handler to be invoked, even when the packet is
properly aligned, and then there's jffs2/mtd which also relies upon
alignment faults being fixed up.
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