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SubjectRe: [Bug #12872] pwc mmap always fails with EAGAIN
> > > Still valid for 2.6.29-rc8-git5.
> >
> > And not really likely to change until someone with a pwc camera adds
> > of printks to the code to work out why this happens.
> Or does a bisection to figure out the bad commit, because the report
> says that 2.6.28 worked.
> The 'howto bisect' portion of:

Well I did a bisect:
be03d9e8022030c16abf534e33e185bfc3d40eef is first bad commit
commit be03d9e8022030c16abf534e33e185bfc3d40eef
Author: Suresh Siddha <>
Date: Wed Feb 11 11:20:23 2009 -0800

x86, pat: fix warn_on_once() while mapping 0-1MB range with /dev/mem

Jeff Mahoney reported:

> With Suse's hwinfo tool, on -tip:
> WARNING: at arch/x86/mm/pat.c:637 reserve_pfn_range+0x5b/0x26d()

reserve_pfn_range() is not tracking the memory range below 1MB
as non-RAM and as such is inconsistent with similar checks in
reserve_memtype() and free_memtype()

Rename the pagerange_is_ram() to pat_pagerange_is_ram() and add the
"track legacy 1MB region as non RAM" condition.

And also, fix reserve_pfn_range() to return -EINVAL, when the pfn
range is RAM. This is to be consistent with this API design.

Reported-and-tested-by: Jeff Mahoney <>
Signed-off-by: Suresh Siddha <>
Signed-off-by: Venkatesh Pallipadi <>
Signed-off-by: Ingo Molnar <>

:040000 040000 feb3bf21d762e885284cb1bedb5d2c6c0d16811b
b4c2143775386ce15dd49b6749c1f7913d8beb00 M arch

So I ran "git bisect reset ; git revert
be03d9e8022030c16abf534e33e185bfc3d40eef" and rebuild. That worked!

I dont know if this is valid to do, but its working fine.
Its an amd64 system with CONFIG_X86_PAT=y.

Need some feedback ;)


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