Message-ID: <559A545A.80508@internode.on.net>
Date: Mon, 06 Jul 2015 19:41:38 +0930
From: Arthur Marsh <arthur.marsh@internode.on.net>
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To: Peter Zijlstra <peterz@infradead.org>
CC: linux-kernel@vger.kernel.org, Rusty Russell <rusty@rustcorp.com.au>,
        Steven Rostedt <rostedt@goodmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Oleg Nesterov <oleg@redhat.com>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: Re: lock-up with module: Optimize __module_address() using a latched
 RB-tree
References: <55997889.5020101@internode.on.net> <20150706100447.GX3644@twins.programming.kicks-ass.net>
In-Reply-To: <20150706100447.GX3644@twins.programming.kicks-ass.net>
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Peter Zijlstra wrote on 06/07/15 19:34:
> On Mon, Jul 06, 2015 at 04:03:45AM +0930, Arthur Marsh wrote:
>> On this machine, a single core Athlon 64 with a 32 bit current Linus' git
>> head kernel, I get a lock-up early in the boot process. (A dmesg output of a
>> successful boot-up of kernel 4.1.0 up to and slightly passed the point where
>> the git head kernel locks up is attached).
>>
>> A photo of the lock-up appears at:
>>
>> http://www.users.on.net/~arthur.marsh/20150706462.jpg
>
> So building a kernel with your .config (and a similar GCC) I was able to
> match up the Code: with actual compiler output.
>
> The faulting instruction is a dereference of mod->module_core through:
>
> __modules_address()
>    mod_find()
>      latch_tree_find()
>        mod_tree_comp()
>          __mod_tree_val()
>
>      20e0:       8b 90 44 01 00 00       mov    0x144(%eax),%edx
>
> Now eax is NULL, which will have given you the splat.
>
> The curious thing is that the mod pointer is obtained from the
> mod_tree_node structure:
>
>      20d0:       8b 46 fc                mov    -0x4(%esi),%eax
>
> And esi looks like a regular kernel pointer.
>
> Furthermore, we explicitly set the mod pointers in mod_tree_insert()
> before linking in the nodes.
>
> This all has the smell of memory corruption, this gfx card you need to
> pull, you're not accidentally using a binary driver for that?
>

No, it's the standard kernel radeon driver.

If it's of any use I can reboot the machine with the kernel that goes 
boom and the video card removed.

Arthur.
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