linux-kernel - Re: [PATCH -resend 1/1] HPET: unmap unused I/O space

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Message-Id: <20100903131941.06521074.akpm@linux-foundation.org>
Date:	Fri, 3 Sep 2010 13:19:41 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Jiri Slaby <jslaby@...e.cz>
Cc:	linux-kernel@...r.kernel.org, jirislaby@...il.com
Subject: Re: [PATCH -resend 1/1] HPET: unmap unused I/O space

On Fri,  3 Sep 2010 10:27:54 +0200
Jiri Slaby <jslaby@...e.cz> wrote:

> When the initialization code in hpet founds a memory resource and does
> not found IRQ, it does not unmap the memory resource previously
> mapped.
> 
> There are buggy BIOSes which report resources exactly like this and
> what is worse the memory region bases point to normal RAM. This
> normally would not matter since the space is not touched. But when PAT
> is turned on, ioremap causes the page to be uncached and sets this bit
> in page->flags.
> 
> Then when the page is about to be used by the allocator, it is
> reported as:
> BUG: Bad page state in process md5sum  pfn:3ed00
> page:ffffea0000dbd800 count:0 mapcount:0 mapping:(null) index:0x0
> page flags: 0x20000001000000(uncached)
> Pid: 7956, comm: md5sum Not tainted 2.6.34-12-desktop #1
> Call Trace:
>  [<ffffffff810df851>] bad_page+0xb1/0x100
>  [<ffffffff810dfa45>] prep_new_page+0x1a5/0x1c0
>  [<ffffffff810dfe01>] get_page_from_freelist+0x3a1/0x640
>  [<ffffffff810e01af>] __alloc_pages_nodemask+0x10f/0x6b0

Well damn, good detective work.  I wonder how many of those nasty
random bad-page-state bug reports just got fixed.  I dub thee
September's "Hero of the Linux kernel"!

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