Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753789AbbHXALx (ORCPT ); Sun, 23 Aug 2015 20:11:53 -0400 Received: from mail-pd0-f195.google.com ([209.85.192.195]:36100 "EHLO mail-pd0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752500AbbHXALv (ORCPT ); Sun, 23 Aug 2015 20:11:51 -0400 Date: Mon, 24 Aug 2015 01:59:45 +0200 From: Jesper Dangaard Brouer To: "Kirill A. Shutemov" Cc: Andrew Morton , Hugh Dickins , Andrea Arcangeli , Dave Hansen , Vlastimil Babka , Johannes Weiner , Michal Hocko , David Rientjes , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Christoph Lameter Subject: Re: [PATCHv3 4/5] mm: make compound_head() robust Message-ID: <20150824015945.58b25f3a@brouer.com> In-Reply-To: <1439976106-137226-5-git-send-email-kirill.shutemov@linux.intel.com> References: <1439976106-137226-1-git-send-email-kirill.shutemov@linux.intel.com> <1439976106-137226-5-git-send-email-kirill.shutemov@linux.intel.com> Organization: Red Hat Inc. X-Mailer: Claws Mail 3.11.1 (GTK+ 2.24.27; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1773 Lines: 56 On Wed, 19 Aug 2015 12:21:45 +0300 "Kirill A. Shutemov" wrote: > Hugh has pointed that compound_head() call can be unsafe in some > context. There's one example: > [...] > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 0735bc0a351a..a4c4b7d07473 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h [...] > -/* > - * If we access compound page synchronously such as access to > - * allocated page, there is no need to handle tail flag race, so we can > - * check tail flag directly without any synchronization primitive. > - */ > -static inline struct page *compound_head_fast(struct page *page) > -{ > - if (unlikely(PageTail(page))) > - return page->first_page; > - return page; > -} > - [...] > @@ -548,13 +508,7 @@ static inline struct page *virt_to_head_page(const void *x) > { > struct page *page = virt_to_page(x); > > - /* > - * We don't need to worry about synchronization of tail flag > - * when we call virt_to_head_page() since it is only called for > - * already allocated page and this page won't be freed until > - * this virt_to_head_page() is finished. So use _fast variant. > - */ > - return compound_head_fast(page); > + return compound_head(page); > } I hope this does not slow down the SLAB/slub allocator? (which calls virt_to_head_page() frequently) -- Best regards, Jesper Dangaard Brouer MSc.CS, Sr. Network Kernel Developer at Red Hat Author of http://www.iptv-analyzer.org LinkedIn: http://www.linkedin.com/in/brouer -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/