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

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Date:	Wed, 9 Sep 2015 14:40:32 +0300
From:	Nikolay Borisov <kernel@...p.com>
To:	Christoph Lameter <cl@...ux.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 09/08/2015 06:15 PM, Christoph Lameter wrote:
> On Tue, 8 Sep 2015, Nikolay Borisov wrote:
> 
>>> You have read https://www.kernel.org/doc/Documentation/vm/slub.txt?
>>
>> I've read that I'm also following the merge/nomerge thread on the DM
>> mailing list. I guess my understanding is wrong in that if multiple slab
>> caches are merged, then it's enough to just instrument the cache to
>> which they are being merge in order to have them all instrumented? I
>> guess that's not the case, so even though slab caches might be merge
>> they are still somehow considered different entities in the kernel?
> 
> Enabling debugging on bootup disables merging.
> 
> If you switch debug options later then its possible to affect all aliases
> caches. But then these option changes are only allowed to be used in such
> a way as to not affect the object layout. You can switch on sanity checks
> and double free checks I believe but nothing else.

I tried the following:

[root@...nighan vm]# ./slabinfo -da kmalloc-32
Cannot write to dma-kmalloc-32/sanity
[root@...nighan vm]# ./slabinfo -dF kmalloc-32
Cannot write to dma-kmalloc-32/sanity
[root@...nighan vm]# ./slabinfo -dz kmalloc-32
kmalloc-32 not empty cannot enable redzoning
[root@...nighan vm]# ./slabinfo -dp kmalloc-32
kmalloc-32 not empty cannot enable poisoning
[root@...nighan vm]# ./slabinfo -du kmalloc-32
kmalloc-32 not empty cannot enable tracking
[root@...nighan vm]# ./slabinfo -dt ^kmalloc-32$
kmalloc-32 can only enable trace for one slab at a time

I did however had success with enabling tracing but couldn't see where
the output is produced - tried dmesg and the ftrace buffer but nothing
turned up.

But it seems it is not possible to enable any debugging whatsoever, so I
will restor to doing it at boot time. In this case can you advice which
options might not result in very high performance degradation - I'm
thinking of sanity checking and maybe redzoning?


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