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@xxxxxxxxxx>
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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