On Mon, May 31, 2021 at 5:37 PM Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > > On Thu, 27 May 2021 17:46:49 -0700 Mina Almasry <almasrymina@xxxxxxxxxx> wrote: > > > The userfaultfd hugetlb tests detect 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 > > 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 > > Do we have a Fixes: for this, or is it an always-been-there issue? This reproduces as far back as 4.15 kernel. Looks like always-been-there issue.
