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From: Rusty Russell <rusty@rustcorp.com.au>
To: David Rientjes <rientjes@google.com>,
        Mika =?utf-8?Q?Penttil=C3=A4?= <mika.penttila@nextfour.com>
Cc: LKML <linux-kernel@vger.kernel.org>, linux-mm@kvack.org,
        Pekka Enberg <penberg@kernel.org>
Subject: Re: [PATCH v2] mm: make apply_to_page_range more robust
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Date: Thu, 21 Jan 2016 15:28:18 +1030
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David Rientjes <rientjes@google.com> writes:
> On Wed, 20 Jan 2016, Mika Penttilä wrote:
>
>> Recent changes (4.4.0+) in module loader triggered oops on ARM. 
>>     
>> can be 0 triggering the bug  BUG_ON(addr >= end);.
>> 
>> The call path is SyS_init_module()->set_memory_xx()->apply_to_page_range(),
>> and apply_to_page_range gets zero length resulting in triggering :
>>    
>>   BUG_ON(addr >= end)
>> 
>> This is a consequence of changes in module section handling (Rusty CC:ed).
>> This may be triggable only with certain modules and/or gcc versions. 
>> 
>
> Well, what module are you loading to cause this crash?  Why would it be 
> passing size == 0 to apply_to_page_range()?  Again, that sounds like a 
> problem that we _want_ to know about since it is probably the result of 
> buggy code and this patch would be covering it up.

Yes, I'm curious too.  It's certainly possible, since I expected a
zero-length range to do nothing, but let's make sure we're not papering
over some other screwup of mine.

Thanks,
Rusty.