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); _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
