[PATCH] mm, hugetlbfs: Fix new warning in fault-time huge page allocation

[Dave Hansen]

From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>

Kirill reported that he hit:
>> +	if (vma || addr) {
>> +		WARN_ON_ONCE(!addr || addr == -1);
>
> Trinity triggered the WARN for me:

This was just a dumb mistake. I put the WARN_ON() in and planned to
have addr=0 mean "use nid". But, I realized pretty quickly that addr=0
_is_ a valid place to fault. So I made it addr=-1 in
__alloc_buddy_huge_page_no_mpol(), but I did not fix up the WARN_ON().

So hitting the warning in this case was harmless.  But, fix up the
warning condition.

Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Hillf Danton <hillf.zj@xxxxxxxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>

---

 b/mm/hugetlb.c |   10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff -puN mm/hugetlb.c~hugetlbfs-fix-warn mm/hugetlb.c
--- a/mm/hugetlb.c~hugetlbfs-fix-warn	2015-10-21 14:40:15.809961389 -0700
+++ b/mm/hugetlb.c	2015-10-21 14:40:15.814961616 -0700
@@ -1520,8 +1520,14 @@ static struct page *__alloc_buddy_huge_p
 	if (hstate_is_gigantic(h))
 		return NULL;
 
-	if (vma || addr) {
-		VM_WARN_ON_ONCE(!addr || addr == -1);
+	/*
+	 * Make sure that anyone specifying 'nid' is not also
+	 * specifying a VMA.  This makes sure the caller is
+	 * picking _one_ of the modes with which we can call this
+	 * function, not both.
+	 */
+	if (vma || (addr != -1)) {
+		VM_WARN_ON_ONCE(addr == -1);
 		VM_WARN_ON_ONCE(nid != NUMA_NO_NODE);
 	}
 	/*
_
--
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