Re: alignment faults in 3.6

On Fri, Oct 12, 2012 at 12:04:23PM +0200, Eric Dumazet wrote:

On Fri, 2012-10-12 at 10:03 +0100, Russell King - ARM Linux wrote:

quoted

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.

Oh well.

We normally make sure we dont have alignment faults on arches that dont
have CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS (or a non null NET_IP_ALIGN)

So if you find an offender, please report a bug, because I can guarantee
you we will _fix_ it.

I think one change I will make to the ARM alignment fixup is to get it
to record the last PC where a misaligned kernel fault occurred, and
report it via our statistics procfs file.  That should allow us to
track down where some of these occur.

They aren't anywhere near regular though - looking at the statistics, my
firewall seems to do an average of around 2-3 a day, and a web server
around 7-8 a day.