mm/hugetlb: vma_has_reserves() needs to handle fallocate hole punch

In vma_has_reserves(), the current assumption is that reserves are
always present for shared mappings.  However, this will not be the case
with fallocate hole punch.  When punching a hole, the present page will
be deleted as well as the region/reserve map entry (and hence any
reservation).  vma_has_reserves is passed "chg" which indicates whether
or not a region/reserve map is present.  Use this to determine if
reserves are actually present or were removed via hole punch.

Signed-off-by: Mike Kravetz <[email protected]>
Reviewed-by: Naoya Horiguchi <[email protected]>
Acked-by: Hillf Danton <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: Aneesh Kumar <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Michal Hocko <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

1 files changed, 13 insertions, 2 deletions

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 61c52cd5f77b..bd12e8c8bc7b 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -801,8 +801,19 @@ static bool vma_has_reserves(struct vm_area_struct *vma, long chg)
 	}
 
 	/* Shared mappings always use reserves */
-	if (vma->vm_flags & VM_MAYSHARE)
-		return true;
+	if (vma->vm_flags & VM_MAYSHARE) {
+		/*
+		 * We know VM_NORESERVE is not set.  Therefore, there SHOULD
+		 * be a region map for all pages.  The only situation where
+		 * there is no region map is if a hole was punched via
+		 * fallocate.  In this case, there really are no reverves to
+		 * use.  This situation is indicated if chg != 0.
+		 */
+		if (chg)
+			return false;
+		else
+			return true;
+	}
 
 	/*
 	 * Only the process that called mmap() has reserves for