Messages in this thread | | | Date | Mon, 23 Dec 2013 12:43:00 +0100 | From | Andrea Arcangeli <> | Subject | Re: [PATCH 1/1] mm: fix the theoretical compound_lock() vs prep_new_page() race |
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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 <oleg@redhat.com>
Acked-by: Andrea Arcangeli <aarcange@redhat.com>
Only one improvement possible, the smp_wmb() could have been put under CONFIG_TRANSPARENT_HUGEPAGE somehow. No difference for x86-64 though.
Thanks, Andrea
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