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

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Date:	Mon, 13 Oct 2014 23:22:37 +0300 (EEST)
From:	mroos@...ux.ee
To:	David Miller <davem@...emloft.net>
cc:	Linux Kernel list <linux-kernel@...r.kernel.org>, cl@...ux.com,
	penberg@...nel.org, rientjes@...gle.com, iamjoonsoo.kim@....com,
	akpm@...ux-foundation.org, linux-mm@...ck.org,
	sparclinux@...r.kernel.org
Subject: Re: unaligned accesses in SLAB etc.

> From: David Miller <davem@...emloft.net>
> Date: Sat, 11 Oct 2014 22:15:10 -0400 (EDT)
> 
> > 
> > I'm getting tons of the following on sparc64:
> > 
> > [603965.383447] Kernel unaligned access at TPC[546b58] free_block+0x98/0x1a0
> > [603965.396987] Kernel unaligned access at TPC[546b60] free_block+0xa0/0x1a0
> > [603965.410523] Kernel unaligned access at TPC[546b58] free_block+0x98/0x1a0

> In all of the cases, the address is 4-byte aligned but not 8-byte
> aligned.  And they are vmalloc addresses.
> 
> Which made me suspect the percpu commit:
> 
> ====================
> commit bf0dea23a9c094ae869a88bb694fbe966671bf6d
> Author: Joonsoo Kim <iamjoonsoo.kim@....com>
> Date:   Thu Oct 9 15:26:27 2014 -0700
> 
>     mm/slab: use percpu allocator for cpu cache
> ====================
> 
> And indeed, reverting this commit fixes the problem.

I tested Joonsoo Kim's fix and it gets rid of the kernel unaligned 
access messages, yes.

But the instability on UltraSparc II era machines still remains - 
occassional Bus Errors during kernel compilation, messages like this:

sh[11771]: segfault at ffd6a4d1 ip 00000000f7cc5714 (rpc 00000000f7cc562c) sp 00000000ffd69d90 error 30002 in libc-2.19.so[f7c44000+16a000]

-- 
Meelis Roos (mroos@...ux.ee)
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