linux-kernel - Re: unaligned accesses in SLAB etc.

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Message-Id: <20141016.162001.599580415052560455.davem@redhat.com>
Date:	Thu, 16 Oct 2014 16:20:01 -0400 (EDT)
From:	David Miller <davem@...hat.com>
To:	mroos@...ux.ee
Cc:	iamjoonsoo.kim@....com, linux-kernel@...r.kernel.org, cl@...ux.com,
	penberg@...nel.org, rientjes@...gle.com, akpm@...ux-foundation.org,
	linux-mm@...ck.org, sparclinux@...r.kernel.org
Subject: Re: unaligned accesses in SLAB etc.

From: Meelis Roos <mroos@...ux.ee>
Date: Thu, 16 Oct 2014 23:16:44 +0300 (EEST)

>> > scripts/Makefile.build:352: recipe for target 'sound/modules.order' failed
>> > make[1]: *** [sound/modules.order] Bus error
>> > make[1]: *** Deleting file 'sound/modules.order'
>> > Makefile:929: recipe for target 'sound' failed
>> 
>> I just reproduced this on my Sun Blade 2500, so it can trigger on UltraSPARC-IIIi
>> systems too.
> 
> My bisection led to the folloowing commit but it seems irrelevant (I 
> have no sun4v on these machines):
> 
> 4ccb9272892c33ef1c19a783cfa87103b30c2784 is the first bad commit
> commit 4ccb9272892c33ef1c19a783cfa87103b30c2784
> Author: bob picco <bpicco@...oft.net>
> Date:   Tue Sep 16 09:26:47 2014 -0400
> 
>     sparc64: sun4v TLB error power off events
> 
> 
> However, the following chunk sound slightly suspicious:
> 
> +       if (fault_code & FAULT_CODE_BAD_RA)
> +               goto do_sigbus;
> +
> 
> because SIGNUS is what I got. For some machines, it killed chekroot 
> during startup, for some shells under some circumstances, for some sshd.

Good catch!

So I'm going to audit all the code paths to make sure we don't put garbage
into the fault_code value.
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