From: Larry Woodman <lwoodman@redhat.com>
To: Rik van Riel <riel@redhat.com>
Cc: Hugh Dickins <hughd@google.com>, Mel Gorman <mgorman@suse.de>,
Michal Hocko <mhocko@suse.cz>, Linux-MM <linux-mm@kvack.org>,
David Gibson <david@gibson.dropbear.id.au>,
Ken Chen <kenchen@google.com>,
Cong Wang <xiyou.wangcong@gmail.com>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH -alternative] mm: hugetlbfs: Close race during teardown of hugetlbfs shared page tables V2 (resend)
Date: Thu, 26 Jul 2012 23:48:56 -0400 [thread overview]
Message-ID: <50120FA8.20409@redhat.com> (raw)
In-Reply-To: <50118E7F.8000609@redhat.com>
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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WARNING: multiple messages have this Message-ID (diff)
From: Larry Woodman <lwoodman@redhat.com>
To: Rik van Riel <riel@redhat.com>
Cc: Hugh Dickins <hughd@google.com>, Mel Gorman <mgorman@suse.de>,
Michal Hocko <mhocko@suse.cz>, Linux-MM <linux-mm@kvack.org>,
David Gibson <david@gibson.dropbear.id.au>,
Ken Chen <kenchen@google.com>,
Cong Wang <xiyou.wangcong@gmail.com>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH -alternative] mm: hugetlbfs: Close race during teardown of hugetlbfs shared page tables V2 (resend)
Date: Thu, 26 Jul 2012 23:48:56 -0400 [thread overview]
Message-ID: <50120FA8.20409@redhat.com> (raw)
In-Reply-To: <50118E7F.8000609@redhat.com>
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
next prev parent reply other threads:[~2012-07-27 3:49 UTC|newest]
Thread overview: 100+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-07-20 13:49 [PATCH] mm: hugetlbfs: Close race during teardown of hugetlbfs shared page tables v2 Mel Gorman
2012-07-20 13:49 ` Mel Gorman
2012-07-20 14:11 ` [PATCH] mm: hugetlbfs: Close race during teardown of hugetlbfs shared page tables V2 (resend) Mel Gorman
2012-07-20 14:11 ` Mel Gorman
2012-07-20 14:29 ` Michal Hocko
2012-07-20 14:29 ` Michal Hocko
2012-07-20 14:37 ` Mel Gorman
2012-07-20 14:37 ` Mel Gorman
2012-07-20 14:40 ` Michal Hocko
2012-07-20 14:40 ` Michal Hocko
2012-07-20 14:36 ` [PATCH -alternative] " Michal Hocko
2012-07-20 14:36 ` Michal Hocko
2012-07-20 14:51 ` Mel Gorman
2012-07-20 14:51 ` Mel Gorman
2012-07-23 4:04 ` Hugh Dickins
2012-07-23 4:04 ` Hugh Dickins
2012-07-23 11:40 ` Mel Gorman
2012-07-23 11:40 ` Mel Gorman
2012-07-24 1:08 ` Hugh Dickins
2012-07-24 1:08 ` Hugh Dickins
2012-07-24 8:32 ` Michal Hocko
2012-07-24 8:32 ` Michal Hocko
2012-07-24 9:34 ` Mel Gorman
2012-07-24 9:34 ` Mel Gorman
2012-07-24 10:04 ` Michal Hocko
2012-07-24 10:04 ` Michal Hocko
2012-07-24 19:23 ` Hugh Dickins
2012-07-24 19:23 ` Hugh Dickins
2012-07-25 8:36 ` Mel Gorman
2012-07-25 8:36 ` Mel Gorman
2012-07-26 17:42 ` Rik van Riel
2012-07-26 17:42 ` Rik van Riel
2012-07-26 18:04 ` Larry Woodman
2012-07-26 18:04 ` Larry Woodman
2012-07-27 8:42 ` Mel Gorman
2012-07-27 8:42 ` Mel Gorman
2012-07-26 18:37 ` Rik van Riel
2012-07-26 18:37 ` Rik van Riel
2012-07-26 21:03 ` Larry Woodman
2012-07-26 21:03 ` Larry Woodman
2012-07-27 3:48 ` Larry Woodman [this message]
2012-07-27 3:48 ` Larry Woodman
2012-07-27 10:10 ` Larry Woodman
2012-07-27 10:10 ` Larry Woodman
2012-07-27 10:23 ` Mel Gorman
2012-07-27 10:23 ` Mel Gorman
2012-07-27 10:36 ` Larry Woodman
2012-07-27 10:36 ` Larry Woodman
2012-07-30 19:11 ` Larry Woodman
2012-07-30 19:11 ` Larry Woodman
2012-07-31 12:16 ` Hillf Danton
2012-07-31 12:16 ` Hillf Danton
2012-07-31 12:46 ` Mel Gorman
2012-07-31 12:46 ` Mel Gorman
2012-07-31 13:07 ` Larry Woodman
2012-07-31 13:07 ` Larry Woodman
2012-07-31 13:29 ` Mel Gorman
2012-07-31 13:29 ` Mel Gorman
2012-07-31 13:21 ` Michal Hocko
2012-07-31 13:21 ` Michal Hocko
2012-07-31 17:49 ` Larry Woodman
2012-07-31 17:49 ` Larry Woodman
2012-07-31 20:06 ` Michal Hocko
2012-07-31 20:06 ` Michal Hocko
2012-07-31 20:57 ` Larry Woodman
2012-07-31 20:57 ` Larry Woodman
2012-08-01 2:45 ` Larry Woodman
2012-08-01 2:45 ` Larry Woodman
2012-08-01 8:20 ` Michal Hocko
2012-08-01 8:20 ` Michal Hocko
2012-08-01 12:32 ` Michal Hocko
2012-08-01 12:32 ` Michal Hocko
2012-08-01 15:06 ` Larry Woodman
2012-08-01 15:06 ` Larry Woodman
2012-08-02 7:19 ` Michal Hocko
2012-08-02 7:19 ` Michal Hocko
2012-08-02 7:37 ` Mel Gorman
2012-08-02 7:37 ` Mel Gorman
2012-08-02 12:36 ` Michal Hocko
2012-08-02 12:36 ` Michal Hocko
2012-08-02 13:33 ` Mel Gorman
2012-08-02 13:33 ` Mel Gorman
2012-08-02 13:53 ` Michal Hocko
2012-08-02 13:53 ` Michal Hocko
2012-07-31 18:03 ` Rik van Riel
2012-07-31 18:03 ` Rik van Riel
2012-07-26 18:31 ` Rik van Riel
2012-07-26 18:31 ` Rik van Riel
2012-07-27 9:02 ` Michal Hocko
2012-07-27 9:02 ` Michal Hocko
2012-07-26 16:01 ` [PATCH] mm: hugetlbfs: Close race during teardown of hugetlbfs shared page tables v2 Larry Woodman
2012-07-26 16:01 ` Larry Woodman
2012-07-27 8:47 ` Mel Gorman
2012-07-27 8:47 ` Mel Gorman
2012-07-26 21:00 ` Rik van Riel
2012-07-26 21:00 ` Rik van Riel
2012-07-26 21:54 ` Hugh Dickins
2012-07-26 21:54 ` Hugh Dickins
2012-07-27 8:52 ` Mel Gorman
2012-07-27 8:52 ` Mel Gorman
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