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Date:	Thu, 22 May 2014 00:22:40 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Greg Kroah-Hartmann <gregkh@...uxfoundation.org>
CC:	Francesco Ruggeri <fruggeri@...sta.com>,
	Hannes Reinecke <hare@...e.de>, linux-kernel@...r.kernel.org
Subject: Re: pci: kernel crash in bus_find_device

On 05/22/2014 12:14 AM, Greg Kroah-Hartmann wrote:
> On Wed, May 21, 2014 at 03:59:58PM -0700, Guenter Roeck wrote:
>> On Wed, May 21, 2014 at 01:04:04PM -0700, Francesco Ruggeri wrote:
>>> I have been using an x86 platform.
>>> When I started working on it I got early crashes until I added the
>>> check for p not NULL in
>>>
>>> +void bus_release_device(struct device *dev)
>>> +{
>>> + struct device_private *p = dev->p;
>>> +
>>> + if (p && klist_node_attached(&p->knode_bus))
>>> + klist_put_last(&p->knode_bus);
>>> +}
>>> +
>>>
>>> Maybe on powerpc *p is overriden between device_del and device_release?
>>>
>>> Or maybe some of the BUG_ONs in the patch? The ones on knode_dead are
>>> treated as WARN_ONs in the current klist code.
>>> The one in BUG_ON(!klist_dec_and_del(n)); is new, and in my tests I
>>> ran into it without the second patch (but only when I ran my module
>>> and tests).
>>>
>> Hi Francesco,
>>
>> I replaced the BUG_ON with WARN_ON; still crashes.
>>
>> Anyway, the problem seems to be known. I found two related exchanges.
>>
>> [1] describes pretty much the same problem. I don't see if/where it was
>> ever fixed, though.
>>
>> [2] is a patch to fix the problem. It did not apply cleanly to 3.14,
>> so I had to make some adjustments in klist_iter_init_node. Resulting
>> patch is below. With this patch, the problem is gone. It is not perfect,
>> as it aborts the loop if it encounters a deleted kobject, but it is better
>> than nothing. Unfortunately, the patch never made it upstream; no idea why.
>> Copying the author and Greg to get additional feedback.
>>
>> Guenter
>>
>> [1] https://lkml.org/lkml/2008/10/26/79
>> [2] https://lkml.org/lkml/2012/4/16/218
>
> 2 years ago?  I have no idea what was up with that, sorry...
>

Ok, but do you have comments on the patch itself in its current version ?

Guenter

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