linux-kernel - Re: Top kernel oopses/warnings for the week of May 30th 2008

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Message-ID: <alpine.LFD.1.10.0805301517500.3141@woody.linux-foundation.org>
Date:	Fri, 30 May 2008 15:30:06 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Arjan van de Ven <arjan@...ux.intel.com>
cc:	Hugh Dickins <hugh@...itas.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, Greg KH <greg@...ah.com>,
	Jeff Garzik <jeff@...zik.org>
Subject: Re: Top kernel oopses/warnings for the week of May 30th 2008

On Fri, 30 May 2008, Arjan van de Ven wrote:
> 
> ok for some it did gather this information, and it is
> 
> kernel BUG at mm/highmem.c:319!

That's just _odd_. The call chain actually has kmap() in it, and kmap 
does:

	if (!PageHighMem(page))
		return page_address(page);
	return kmap_high(page);

so if it's the one at line 319, which says

	BUG_ON(!PageHighMem(page));

then I wonder what happened to that PageHighMem() test of the page in 
between..

Ahh.. Not the same "page". It looks like it's in the 
flush_all_zero_pkmaps() path, and it's clearing some _other_ page in the 
pkmap table in order to make room for the new one. So the page that causes 
problems is from here:

	 page = pte_page(pkmap_page_table[i]);

rather than the one we're trying to map.

Not that it explains the BUG_ON(). We should only insert page table 
entries into the pkmap_page_table[] array in map_new_virtual(), which in 
turn is only called from kmap_high(), which in turn means that *those* 
pages have also gine through the PageHighMem() test.

So it sounds like we either
 - have corruption in pkmap_page_table[]
 - or pte_page() doesn't reverse mk_pte(page) propely, and one or the 
   other is broken.

Does anybody know if the fc9 x86-32 kernel is built with PAE enabled? 
Might this be another PAE bit-masking bug and thus possibly fixed by the 
PTE_MASK changes?

		Linus

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