# CCed Andrew, and linux-mm
On Thu, Jul 17, 2014 at 11:59:36PM +0200, Guillaume Morin wrote:
> On 17 Jul 17:33, Naoya Horiguchi wrote:
...
> > And it seems that this also happens on v3.16-rc5.
> > So it might be an upstream bug, not a stable-specific matter.
>
> That's my understanding as well. I just reported it for 3.4 and 3.14
> since these were the kernels I could easily try my original test with.
OK. I've checked the fix you suggested below on mainline, and
it passed our test program.
> > It looks strange to me that the problem is gone by removing the commit
> > 4a705fef98 (although I confirmed it is,) because the kernel's behavior
> > shouldn't change unless (is_hugetlb_entry_migration(entry) ||
> > is_hugetlb_entry_hwpoisoned(entry)) is true. And I checked with systemtap
> > that both these check returned false in the above test program.
> > So I'm wondering why the commit makes difference for this test program.
>
> I don't know why I am just thinking about that now. Isn't this the fact
> that your patch moved the huge_ptep_get() before
> huge_ptep_set_wrprotect() in the pte_present() cow case?
Ah, right. I was really blind :(
>
> Actually, I've just tried to re-add the huge_ptep_get call for that
> case and it's fixing the problem for me...
>
> Hmm, want a patch?
Thanks, but it's just a oneliner, so I wrote the one.
Naoya Horiguchi
---
From: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Date: Thu, 17 Jul 2014 18:11:22 -0400
Subject: [PATCH] mm: hugetlb: fix copy_hugetlb_page_range()
commit 4a705fef98 ("hugetlb: fix copy_hugetlb_page_range() to handle
migration/hwpoisoned entry") changed the order of huge_ptep_set_wrprotect()
and huge_ptep_get(), which leads to break some workload like hugepage-backed
heap allocation via libhugetlbfs. This patch fixes it.
The test program for the problem is shown below:
$ cat heap.c
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#define HPS 0x200000
int main() {
int i;
char *p = malloc(HPS);
memset(p, '1', HPS);
for (i = 0; i < 5; i++) {
if (!fork()) {
memset(p, '2', HPS);
p = malloc(HPS);
memset(p, '3', HPS);
free(p);
return 0;
}
}
sleep(1);
free(p);
return 0;
}
$ export HUGETLB_MORECORE=yes ; export HUGETLB_NO_PREFAULT= ; hugectl --heap ./heap
Reported-by: Guillaume Morin <guillaume@xxxxxxxxxxx>
Suggested-by: Guillaume Morin <guillaume@xxxxxxxxxxx>
Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
mm/hugetlb.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index a8d4155eb019..7263c770e9b3 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2597,6 +2597,7 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
} else {
if (cow)
huge_ptep_set_wrprotect(src, addr, src_pte);
+ entry = huge_ptep_get(src_pte);
ptepage = pte_page(entry);
get_page(ptepage);
page_dup_rmap(ptepage);
--
1.9.3
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