On Fri, 3 Jan 2014 20:55:47 +0100 Oleg Nesterov <o...@redhat.com> 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(). Would be useful to mention that these things are happening inside prep_compound_opage() (yes?). > 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. I don't get it. We're in prep_new_page() - this page is freshly allocated and no other thread yet has any means by which to look it up and start fiddling with it? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
