Re: [PATCH] userfaultfd/shmem: fix minor fault page leak

On Mon, Mar 22, 2021 at 01:48:35PM -0700, Axel Rasmussen wrote:

This fix is analogous to Peter Xu's fix for hugetlb [0]. If we don't put_page() after getting the page out of the page cache, we leak the reference.

The fix can be verified by checking /proc/meminfo and running the userfaultfd selftest in shmem mode. Without the fix, we see MemFree / MemAvailable steadily decreasing with each run of the test. With the fix, memory is correctly freed after the test program exits.

Fixes: 00da60b9d0a0 ("userfaultfd: support minor fault handling for shmem") Signed-off-by: Axel Rasmussen axelrasmussen@google.com

Reviewed-by: Peter Xu peterx@redhat.com