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

Orabug: 21652814

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 <mike.kravetz@oracle.com>
Reviewed-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Acked-by: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Aneesh Kumar <aneesh.kumar@linux.vnet.ibm.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
(cherry picked from commit 320fb799e7cedc1edb96fd69c686547c731d5fc8)
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index aafb704cb69029827705a81ffcff7e3355374a08..70d1a213a6a83e6c904ef7f3cdb4f43246a2972b 100644 (file)
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -796,8 +796,19 @@ 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