On 5/27/21 5:46 PM, Mina Almasry wrote:
The userfaultfd hugetlb tests detect a resv_huge_pages underflow. This
Perhaps say, The userfaultfd hugetlb tests cause a resv_huge_pages underflow. This
happens when hugetlb_mcopy_atomic_pte() is called with !is_continue on an index for which we already have a page in the cache. When this happens, we allocate a second page, double consuming the reservation, and then fail to insert the page into the cache and return -EEXIST.
To fix this, we first if there exists a page in the cache which already
To fix this, we first check if there is a page in the cache which already
To fix this, we first if there exists a page in the cache which already consumed the reservation, and return -EEXIST immediately if so.
There is still a rare condition where we fail to copy the page contents AND race with a call for hugetlb_no_page() for this index and again we will underflow resv_huge_pages. That is fixed in a more complicated patch not targeted for -stable.
Test: Hacked the code locally such that resv_huge_pages underflows produce a warning, then:
./tools/testing/selftests/vm/userfaultfd hugetlb_shared 10 2 /tmp/kokonut_test/huge/userfaultfd_test && echo test success ./tools/testing/selftests/vm/userfaultfd hugetlb 10 2 /tmp/kokonut_test/huge/userfaultfd_test && echo test success
Both tests succeed and produce no warnings. After the test runs number of free/resv hugepages is correct.
Signed-off-by: Mina Almasry almasrymina@google.com Cc: Axel Rasmussen axelrasmussen@google.com Cc: Peter Xu peterx@redhat.com Cc: linux-mm@kvack.org Cc: Mike Kravetz mike.kravetz@oracle.com Cc: Andrew Morton akpm@linux-foundation.org Cc: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org Cc: stable@vger.kernel.org
mm/hugetlb.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-)
Code changes are fine. Thanks,
Reviewed-by: Mike Kravetz mike.kravetz@oracle.com