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 --- mm/shmem.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/mm/shmem.c b/mm/shmem.c index ef8c9f5e92fc..d2e0e81b7d2e 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -1831,6 +1831,7 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
if (page && vma && userfaultfd_minor(vma)) { unlock_page(page); + put_page(page); *fault_type = handle_userfault(vmf, VM_UFFD_MINOR); return 0; }