On Thu, Dec 19, 2013 at 08:09:20PM +0100, Oleg Nesterov wrote: > get/put_page(thp_tail) paths do get_page_unless_zero(page_head) + > compound_lock(). In theory this page_head can be already freed and > reallocated as alloc_pages(__GFP_COMP, smaller_order). In this case > get_page_unless_zero() can succeed right after set_page_refcounted(), > and compound_lock() can race with the non-atomic __SetPageHead(). > > Perhaps we should rework the thp locking (under discussion), but > until then this patch moves set_page_refcounted() and adds wmb() > to ensure that page->_count != 0 comes as a last change. > > I am not sure about other callers of set_page_refcounted(), but at > first glance they look fine to me. > > Signed-off-by: Oleg Nesterov <[email protected]>
Acked-by: Andrea Arcangeli <[email protected]> Only one improvement possible, the smp_wmb() could have been put under CONFIG_TRANSPARENT_HUGEPAGE somehow. No difference for x86-64 though. Thanks, Andrea -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
