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Subject2.6.33 pagemap endless read loop

An LTP run on x86-64/2.6.33-rc3 run right now results in "proc01" hanging

lr-x------ 1 root root 64 2010-01-10 02:28 7 -> /proc/2679/task/2679/pagemap
strace shows an endless loop of

read(7, "\0\0\0\0\0\0\0\6\0\0\0\0\0\0\0\6\0\0\0\0\0\0\0\6\0\0\0"..., 1024) = 1024
read(7, "\0\0\0\0\0\0\0\6\0\0\0\0\0\0\0\6\0\0\0\0\0\0\0\6\0\0\0"..., 1024) = 1024
read(7, "\0\0\0\0\0\0\0\6\0\0\0\0\0\0\0\6\0\0\0\0\0\0\0\6\0\0\0"..., 1024) = 1024
read(7, "\0\0\0\0\0\0\0\6\0\0\0\0\0\0\0\6\0\0\0\0\0\0\0\6\0\0\0"..., 1024) = 1024
read(7, "\0\0\0\0\0\0\0\6\0\0\0\0\0\0\0\6\0\0\0\0\0\0\0\6\0\0\0"..., 1024) = 1024
read(7, "\0\0\0\0\0\0\0\6\0\0\0\0\0\0\0\6\0\0\0\0\0\0\0\6\0\0\0"..., 1024) = 1024
read(7, "\0\0\0\0\0\0\0\6\0\0\0\0\0\0\0\6\0\0\0\0\0\0\0\6\0\0\0"..., 1024) = 10

cat of that file hangs in the same way so it seems like a kernel bug.
A cat of /proc/2679/pagemap also hangs, in fact any pagemap cat seems to.

I tried to revert the latest change from Horiguchi-san:

commit 5dc37642cbce34619e4588a9f0bdad1d2f870956
Author: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Date: Mon Dec 14 18:00:01 2009 -0800

mm hugetlb: add hugepage support to pagemap

but that didn't fix it, so it must be something else.

Haven't done further bisect or anything, should be easy to reproduce.

-Andi

--
ak@linux.intel.com -- Speaking for myself only.


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