linux-kernel - Re: 2.6.25-rc2-mm1: WARNING at arch/x86/mm/ioremap.c:129

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Message-ID: <47CADC9D.9090403@linux.intel.com>
Date:	Sun, 02 Mar 2008 08:58:05 -0800
From:	Arjan van de Ven <arjan@...ux.intel.com>
To:	Arjan van de Ven <arjan@...ux.intel.com>,
	Gabriel C <nix.or.die@...glemail.com>,
	Laurent Riffard <laurent.riffard@...e.fr>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Stuart Bennett <sb476@....ac.uk>,
	Len Brown <lenb@...nel.org>, tglx@...utronix.de,
	mingo@...hat.com
Subject: Re: 2.6.25-rc2-mm1: WARNING at arch/x86/mm/ioremap.c:129

Fabio Checconi wrote:
> [cc'd relevant maintainers]
> 
> Hi,
> 
>> From: Arjan van de Ven <arjan@...ux.intel.com>
>> Date: Mon, Feb 25, 2008 02:44:53PM -0800
>>
>> Gabriel C wrote:
> ...
>>> With your patch from 
>>> http://marc.info/?l=linux-kernel&m=120336371506283&w=2 I don't have a 
>>> warning anymore.
>>>
>> that is ... odd since it's the same in theory, just with some added 
>> printk's ;-(
> 
> the same here on 2.6.25-rc3, with the innocent ibmphp_access_ebda()
> that fires the WARN_ON() in __ioremap() asking for the pfn 0, even
> after the page_is_ram() change.  With your patch the warning
> disappears.
> 
> I think this is because the pfn checked by the original code (before
> your patch) is the one after the last iteration, while your patch
> checks for each pfn that is going to be mapped.  The latter should
> be the intended behavior.  If I've understood the problem, the
> (trivial) patch below should fix it.
> 
> Also, note that if last_addr is at the beginning of a page we can
> __ioremap() normal RAM (in fact we only emit the warning with the
> old code, instead of returning NULL.)  Is that possible/intended
> behavior?  If not the loop should do one more iteration.
> 
> 
> __ioremap() emits a warning if the pfn after the last one it's going
> to map is of normal ram.  Correct this and emit the warning (once)
> only if one of the asked pages is.
> 


looks good to me; Ingo please apply
(Note: if no legit users show up I want to just remove support for mapping ram altogether
in 2.6.26 or so)
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