mm, thp: fix infinite loop on memcg OOM
Masayoshi Mizuma reported a bug with the hang of an application under
the memcg limit. It happens on write-protection fault to huge zero page
If we successfully allocate a huge page to replace zero page but hit the
memcg limit we need to split the zero page with split_huge_page_pmd()
and fallback to small pages.
The other part of the problem is that VM_FAULT_OOM has special meaning
in do_huge_pmd_wp_page() context. __handle_mm_fault() expects the page
to be split if it sees VM_FAULT_OOM and it will will retry page fault
handling. This causes an infinite loop if the page was not split.
do_huge_pmd_wp_zero_page_fallback() can return VM_FAULT_OOM if it failed
to allocate one small page, so fallback to small pages will not help.
The solution for this part is to replace VM_FAULT_OOM with
VM_FAULT_FALLBACK is fallback required.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reported-by: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/memory.c b/mm/memory.c
index 5f2001a..22dfa61 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3704,7 +3704,6 @@
if (unlikely(is_vm_hugetlb_page(vma)))
return hugetlb_fault(mm, vma, address, flags);
-retry:
pgd = pgd_offset(mm, address);
pud = pud_alloc(mm, pgd, address);
if (!pud)
@@ -3742,20 +3741,13 @@
if (dirty && !pmd_write(orig_pmd)) {
ret = do_huge_pmd_wp_page(mm, vma, address, pmd,
orig_pmd);
- /*
- * If COW results in an oom, the huge pmd will
- * have been split, so retry the fault on the
- * pte for a smaller charge.
- */
- if (unlikely(ret & VM_FAULT_OOM))
- goto retry;
- return ret;
+ if (!(ret & VM_FAULT_FALLBACK))
+ return ret;
} else {
huge_pmd_set_accessed(mm, vma, address, pmd,
orig_pmd, dirty);
+ return 0;
}
-
- return 0;
}
}