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@xxxxxxxxxx> > Cc: Axel Rasmussen <axelrasmussen@xxxxxxxxxx> > Cc: Peter Xu <peterx@xxxxxxxxxx> > Cc: linux-mm@xxxxxxxxx > Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > Cc: linux-mm@xxxxxxxxx > Cc: linux-kernel@xxxxxxxxxxxxxxx > Cc: stable@xxxxxxxxxxxxxxx > > --- > mm/hugetlb.c | 14 ++++++++++++-- > 1 file changed, 12 insertions(+), 2 deletions(-) Code changes are fine. Thanks, Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx> -- Mike Kravetz
