On 7/30/19 5:44 PM, Mike Kravetz wrote:
> A SIGBUS is the normal behavior for a hugetlb page fault failure due to
> lack of huge pages. Ugly, but that is the design. I do not believe this
> test should not be experiencing this due to reservations taken at mmap
> time. However, the test is combining faults, soft offline and page
> migrations, so the there are lots of moving parts.
>
> I'll continue to investigate.
There appears to be a race with hugetlb_fault and try_to_unmap_one of
the migration path.
Can you try this patch in your environment? I am not sure if it will
be the final fix, but just wanted to see if it addresses issue for you.
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index ede7e7f5d1ab..f3156c5432e3 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -3856,6 +3856,20 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm,
page = alloc_huge_page(vma, haddr, 0);
if (IS_ERR(page)) {
+ /*
+ * We could race with page migration (try_to_unmap_one)
+ * which is modifying page table with lock. However,
+ * we are not holding lock here. Before returning
+ * error that will SIGBUS caller, get ptl and make
+ * sure there really is no entry.
+ */
+ ptl = huge_pte_lock(h, mm, ptep);
+ if (!huge_pte_none(huge_ptep_get(ptep))) {
+ ret = 0;
+ spin_unlock(ptl);
+ goto out;
+ }
+ spin_unlock(ptl);
ret = vmf_error(PTR_ERR(page));
goto out;
}
