Messages in this thread Patch in this message | | | Date | Thu, 26 Jul 2012 23:48:56 -0400 | From | Larry Woodman <> | Subject | Re: [PATCH -alternative] mm: hugetlbfs: Close race during teardown of hugetlbfs shared page tables V2 (resend) |
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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 <hughd@google.com> > > 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
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