From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx206.postini.com [74.125.245.206]) by kanga.kvack.org (Postfix) with SMTP id CB1BC6B0044 for ; Thu, 26 Jul 2012 23:49:04 -0400 (EDT) Message-ID: <50120FA8.20409@redhat.com> Date: Thu, 26 Jul 2012 23:48:56 -0400 From: Larry Woodman Reply-To: lwoodman@redhat.com MIME-Version: 1.0 Subject: Re: [PATCH -alternative] mm: hugetlbfs: Close race during teardown of hugetlbfs shared page tables V2 (resend) References: <20120720134937.GG9222@suse.de> <20120720141108.GH9222@suse.de> <20120720143635.GE12434@tiehlicka.suse.cz> <20120720145121.GJ9222@suse.de> <50118E7F.8000609@redhat.com> In-Reply-To: <50118E7F.8000609@redhat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Rik van Riel Cc: Hugh Dickins , Mel Gorman , Michal Hocko , Linux-MM , David Gibson , Ken Chen , Cong Wang , LKML On 07/26/2012 02:37 PM, Rik van Riel wrote: > On 07/23/2012 12:04 AM, Hugh Dickins wrote: > >> I spent hours trying to dream up a better patch, trying various >> approaches. I think I have a nice one now, what do you think? And >> more importantly, does it work? I have not tried to test it at all, >> that I'm hoping to leave to you, I'm sure you'll attack it with gusto! >> >> If you like it, please take it over and add your comments and signoff >> and send it in. The second part won't come up in your testing, and >> could >> be made a separate patch if you prefer: it's a related point that struck >> me while I was playing with a different approach. >> >> I'm sorely tempted to leave a dangerous pair of eyes off the Cc, >> but that too would be unfair. >> >> Subject-to-your-testing- >> Signed-off-by: Hugh Dickins > > This patch looks good to me. > > Larry, does Hugh's patch survive your testing? > > Like I said earlier, no. However, I finally set up a reproducer that only takes a few seconds on a large system and this totally fixes the problem: ------------------------------------------------------------------------------------------------------------------------- diff --git a/mm/hugetlb.c b/mm/hugetlb.c index c36febb..cc023b8 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -2151,7 +2151,7 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src, goto nomem; /* If the pagetables are shared don't copy or take references */ - if (dst_pte == src_pte) + if (*(unsigned long *)dst_pte == *(unsigned long *)src_pte) continue; spin_lock(&dst->page_table_lock); --------------------------------------------------------------------------------------------------------------------------- When we compare what the src_pte & dst_pte point to instead of their addresses everything works, I suspect there is a missing memory barrier somewhere ??? Larry -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org