linux-kernel - Re: 4.0.0-rc4: panic in free

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Date:	Fri, 20 Mar 2015 09:48:48 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	David Ahern <david.ahern@...cle.com>,
	"David S. Miller" <davem@...emloft.net>
Cc:	linux-mm <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
	sparclinux@...r.kernel.org
Subject: Re: 4.0.0-rc4: panic in free_block

[ Added Davem and the sparc mailing list, since it happens on sparc
and that just makes me suspicious ]

On Fri, Mar 20, 2015 at 8:07 AM, David Ahern <david.ahern@...cle.com> wrote:
> I can easily reproduce the panic below doing a kernel build with make -j N,
> N=128, 256, etc. This is a 1024 cpu system running 4.0.0-rc4.

3.19 is fine? Because I dont' think I've seen any reports like this
for others, and what stands out is sparc (and to a lesser degree "1024
cpus", which obviously gets a lot less testing)

> The top 3 frames are consistently:
>     free_block+0x60
>     cache_flusharray+0xac
>     kmem_cache_free+0xfc
>
> After that one path has been from __mmdrop and the others are like below,
> from remove_vma.
>
> Unable to handle kernel paging request at virtual address 0006100000000000

One thing you *might* check is if the problem goes away if you select
CONFIG_SLUB instead of CONFIG_SLAB. I'd really like to just get rid of
SLAB. The whole "we have multiple different allocators" is a mess and
causes test coverage issues.

Apart from testing with CONFIG_SLUB, if 3.19 is ok and you seem to be
able to "easily reproduce" this, the obvious thing to do is to try to
bisect it.

                         Linus
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