diff options
authorJoonsoo Kim <iamjoonsoo.kim@lge.com>2013-09-11 14:21:06 -0700
committerSteve Capper <steve.capper@linaro.org>2014-06-12 08:48:10 +0100
commitf3e2c9ea1c5576bfd5fbcc55b6f84f44ec150e49 (patch)
parent8d043fc5b9b5ff16b16bb352feb7bd07d3262446 (diff)
mm, hugetlb: add VM_NORESERVE check in vma_has_reserves()
If we map the region with MAP_NORESERVE and MAP_SHARED, we can skip to check reserve counting and eventually we cannot be ensured to allocate a huge page in fault time. With following example code, you can easily find this situation. Assume 2MB, nr_hugepages = 100 fd = hugetlbfs_unlinked_fd(); if (fd < 0) return 1; size = 200 * MB; flag = MAP_SHARED; p = mmap(NULL, size, PROT_READ|PROT_WRITE, flag, fd, 0); if (p == MAP_FAILED) { fprintf(stderr, "mmap() failed: %s\n", strerror(errno)); return -1; } size = 2 * MB; flag = MAP_ANONYMOUS | MAP_SHARED | MAP_HUGETLB | MAP_NORESERVE; p = mmap(NULL, size, PROT_READ|PROT_WRITE, flag, -1, 0); if (p == MAP_FAILED) { fprintf(stderr, "mmap() failed: %s\n", strerror(errno)); } p[0] = '0'; sleep(10); During executing sleep(10), run 'cat /proc/meminfo' on another process. HugePages_Free: 99 HugePages_Rsvd: 100 Number of free should be higher or equal than number of reserve, but this aren't. This represent that non reserved shared mapping steal a reserved page. Non reserved shared mapping should not eat into reserve space. If we consider VM_NORESERVE in vma_has_reserve() and return 0 which mean that we don't have reserved pages, then we check that we have enough free pages in dequeue_huge_page_vma(). This prevent to steal a reserved page. With this change, above test generate a SIGBUG which is correct, because all free pages are reserved and non reserved shared mapping can't get a free page. Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com> Reviewed-by: Wanpeng Li <liwanp@linux.vnet.ibm.com> Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com> Acked-by: Hillf Danton <dhillf@gmail.com> Acked-by: Michal Hocko <mhocko@suse.cz> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Cc: Rik van Riel <riel@redhat.com> Cc: Mel Gorman <mgorman@suse.de> Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Hugh Dickins <hughd@google.com> Cc: Davidlohr Bueso <davidlohr.bueso@hp.com> Cc: David Gibson <david@gibson.dropbear.id.au> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 files changed, 2 insertions, 0 deletions
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index ebd3cc8aa2f..8b5b6a08a1a 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -465,6 +465,8 @@ void reset_vma_resv_huge_pages(struct vm_area_struct *vma)
/* Returns true if the VMA has associated reserve pages */
static int vma_has_reserves(struct vm_area_struct *vma)
+ if (vma->vm_flags & VM_NORESERVE)
+ return 0;
if (vma->vm_flags & VM_MAYSHARE)
return 1;
if (is_vma_resv_set(vma, HPAGE_RESV_OWNER))