The patch titled
Subject: include/linux/page_ref.h: ensure page_ref_unfreeze is ordered against prior accesses
has been added to the -mm tree. Its filename is
mm-page_ref-ensure-page_ref_unfreeze-is-ordered-against-prior-accesses.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-page_ref-ensure-page_ref_unfreeze-is-ordered-against-prior-accesses.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-page_ref-ensure-page_ref_unfreeze-is-ordered-against-prior-accesses.patch
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From: Will Deacon <will.deacon@xxxxxxx>
Subject: include/linux/page_ref.h: ensure page_ref_unfreeze is ordered against prior accesses
page_ref_freeze and page_ref_unfreeze are designed to be used as a pair,
wrapping a critical section where struct pages can be modified without
having to worry about consistency for a concurrent fast-GUP.
Whilst page_ref_freeze has full barrier semantics due to its use of
atomic_cmpxchg, page_ref_unfreeze is implemented using atomic_set, which
doesn't provide any barrier semantics and allows the operation to be
reordered with respect to page modifications in the critical section.
This patch ensures that page_ref_unfreeze is ordered after any critical
section updates, by invoking smp_mb() prior to the atomic_set.
Link: http://lkml.kernel.org/r/1497349722-6731-3-git-send-email-will.deacon@xxxxxxx
Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
Acked-by: Steve Capper <steve.capper@xxxxxxx>
Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/page_ref.h | 1 +
1 file changed, 1 insertion(+)
diff -puN include/linux/page_ref.h~mm-page_ref-ensure-page_ref_unfreeze-is-ordered-against-prior-accesses include/linux/page_ref.h
--- a/include/linux/page_ref.h~mm-page_ref-ensure-page_ref_unfreeze-is-ordered-against-prior-accesses
+++ a/include/linux/page_ref.h
@@ -174,6 +174,7 @@ static inline void page_ref_unfreeze(str
VM_BUG_ON_PAGE(page_count(page) != 0, page);
VM_BUG_ON(count == 0);
+ smp_mb();
atomic_set(&page->_refcount, count);
if (page_ref_tracepoint_active(__tracepoint_page_ref_unfreeze))
__page_ref_unfreeze(page, count);
_
Patches currently in -mm which might be from will.deacon@xxxxxxx are
mm-gup-remove-broken-vm_bug_on_page-compound-check-for-hugepages.patch
mm-page_ref-ensure-page_ref_unfreeze-is-ordered-against-prior-accesses.patch
mm-migrate-stabilise-page-count-when-migrating-transparent-hugepages.patch
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