linux-kernel - Re: Kernel 4.1.6 Panic due to slab corruption

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Date:	Thu, 10 Sep 2015 11:30:31 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Nikolay Borisov <kernel@...p.com>
cc:	"Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
	Marian Marinov <mm@...com>,
	SiteGround Operations <operations@...eground.com>
Subject: Re: Kernel 4.1.6 Panic due to slab corruption

On Thu, 10 Sep 2015, Nikolay Borisov wrote:

> > 	echo 1 >santy_checks
>
> [root@...nighan linux-stable]# cd /sys/kernel/slab/kmalloc-32/
> [root@...nighan kmalloc-32]# echo 1 > sanity_checks
> [root@...nighan kmalloc-32]# cat sanity_checks
> 1
>
> So this works as expected when set by echo. Just for testing I then
> tried the following:
> [root@...nighan kmalloc-32]# slabinfo -d- kmalloc-32
> kmalloc-32 not empty cannot disable sanity checks
>
> [root@...nighan kmalloc-32]# echo 0 > sanity_checks
> [root@...nighan kmalloc-32]# slabinfo -d- kmalloc-32
>
> So turns out slabinfo fails where the raw sys interface succeeds, strange?

Weird. slabinfo needs fixing.

> > do? Could crash the sysem due to overload of messages.
>
> Didn't have that much luck with this one:
> [root@...nighan kmalloc-32]# dmesg -c > /dev/null
> [root@...nighan kmalloc-32]# echo 1 > trace
> -bash: echo: write error: Invalid argument


Huh? There is no check that I am ware of in the slab code that would
return -EINVAL.

> > Sanity checking is ok. But I would think you should be fine with enabling
> > full debugging on the particular caches of interest.
>
> I was just thinking that if enabling debug options disables merging this
> means it won't be sufficient to enable debugging on kmalloc-32 but
> rather before enabling debugging I do need to check which caches were
> aliased and enable debugging on those as well, correct?

Correct.

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