* [merged] powerpc-get_hugepte-dont-put_page-the-wrong-page.patch removed from -mm tree
@ 2011-11-07 20:24 akpm
0 siblings, 0 replies; only message in thread
From: akpm @ 2011-11-07 20:24 UTC (permalink / raw
To: aarcange, a.p.zijlstra, benh, david, hughd, jweiner,
kosaki.motohiro, mgorman
The patch titled
Subject: powerpc: get_hugepte() don't put_page() the wrong page
has been removed from the -mm tree. Its filename was
powerpc-get_hugepte-dont-put_page-the-wrong-page.patch
This patch was dropped because it was merged into mainline or a subsystem tree
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
From: Andrea Arcangeli <aarcange@redhat.com>
Subject: powerpc: get_hugepte() don't put_page() the wrong page
"page" may have changed to point to the next hugepage after the loop
completed, The references have been taken on the head page, so the
put_page must happen there too.
This is a longstanding issue pre-thp inclusion.
It's totally unclear how these page_cache_add_speculative and pte_val(pte)
!= pte_val(*ptep) checks are necessary across all the powerpc gup_fast
code, when x86 doesn't need any of that: there's no way the page can be
freed with irq disabled so we're guaranteed the atomic_inc will happen on
a page with page_count > 0 (so not needing the speculative check). The
pte check is also meaningless on x86: no need to rollback on x86 if the
pte changed, because the pte can still change a CPU tick after the check
succeeded and it won't be rolled back in that case. The important thing
is we got a reference on a valid page that was mapped there a CPU tick
ago. So not knowing the soft tlb refill code of ppc64 in great detail I'm
not removing the "speculative" page_count increase and the pte checks
across all the code, but unless there's a strong reason for it they should
be later cleaned up too.
If a pte can change from huge to non-huge (like it could happen with THP)
passing a pte_t *ptep to gup_hugepte() would also require to repeat the
is_hugepd in gup_hugepte(), but that shouldn't happen with hugetlbfs only
so I'm not altering that.
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <jweiner@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
arch/powerpc/mm/hugetlbpage.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff -puN arch/powerpc/mm/hugetlbpage.c~powerpc-get_hugepte-dont-put_page-the-wrong-page arch/powerpc/mm/hugetlbpage.c
--- a/arch/powerpc/mm/hugetlbpage.c~powerpc-get_hugepte-dont-put_page-the-wrong-page
+++ a/arch/powerpc/mm/hugetlbpage.c
@@ -429,7 +429,7 @@ static noinline int gup_hugepte(pte_t *p
if (unlikely(pte_val(pte) != pte_val(*ptep))) {
/* Could be optimized better */
while (*nr) {
- put_page(page);
+ put_page(head);
(*nr)--;
}
}
_
Patches currently in -mm which might be from aarcange@redhat.com are
origin.patch
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2011-11-07 20:24 [merged] powerpc-get_hugepte-dont-put_page-the-wrong-page.patch removed from -mm tree akpm
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