Re: [PATCH] powerpc: thp: Fix crash on mremap

On Mon, Jan 13, 2014 at 02:17:48PM -0800, Andrew Morton wrote:

On Thu, 2 Jan 2014 04:19:51 +0200 "Kirill A. Shutemov" [off-list ref] wrote:

quoted

On Wed, Jan 01, 2014 at 09:29:05PM +1100, Benjamin Herrenschmidt wrote:

quoted

On Wed, 2014-01-01 at 15:23 +0530, Aneesh Kumar K.V wrote:

quoted

From: "Aneesh Kumar K.V" <redacted>

This patch fix the below crash

NIP [c00000000004cee4] .__hash_page_thp+0x2a4/0x440
LR [c0000000000439ac] .hash_page+0x18c/0x5e0
...
Call Trace:
[c000000736103c40] [00001ffffb000000] 0x1ffffb000000(unreliable)
[437908.479693] [c000000736103d50] [c0000000000439ac] .hash_page+0x18c/0x5e0
[437908.479699] [c000000736103e30] [c00000000000924c] .do_hash_page+0x4c/0x58

On ppc64 we use the pgtable for storing the hpte slot information and
store address to the pgtable at a constant offset (PTRS_PER_PMD) from
pmd. On mremap, when we switch the pmd, we need to withdraw and deposit
the pgtable again, so that we find the pgtable at PTRS_PER_PMD offset
from new pmd.

We also want to move the withdraw and deposit before the set_pmd so
that, when page fault find the pmd as trans huge we can be sure that
pgtable can be located at the offset.

Did this get fixed?

New version: http://thread.gmane.org/gmane.linux.kernel.mm/111809

-- 
 Kirill A. Shutemov