From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Subject: 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@xxxxxxxxxxxxxxx>
Reported-by: Masayoshi Mizuma <m.mizuma@xxxxxxxxxxxxxx>
Reviewed-by: Michal Hocko <mhocko@xxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/huge_memory.c | 9 ++++++---
mm/memory.c | 14 +++-----------
2 files changed, 9 insertions(+), 14 deletions(-)
diff -puN mm/huge_memory.c~mm-thp-fix-infinite-loop-on-memcg-oom mm/huge_memory.c
--- a/mm/huge_memory.c~mm-thp-fix-infinite-loop-on-memcg-oom
+++ a/mm/huge_memory.c
@@ -1166,8 +1166,10 @@ alloc:
} else {
ret = do_huge_pmd_wp_page_fallback(mm, vma, address,
pmd, orig_pmd, page, haddr);
- if (ret & VM_FAULT_OOM)
+ if (ret & VM_FAULT_OOM) {
split_huge_page(page);
+ ret |= VM_FAULT_FALLBACK;
+ }
put_page(page);
}
count_vm_event(THP_FAULT_FALLBACK);
@@ -1179,9 +1181,10 @@ alloc:
if (page) {
split_huge_page(page);
put_page(page);
- }
+ } else
+ split_huge_page_pmd(vma, address, pmd);
+ ret |= VM_FAULT_FALLBACK;
count_vm_event(THP_FAULT_FALLBACK);
- ret |= VM_FAULT_OOM;
goto out;
}
diff -puN mm/memory.c~mm-thp-fix-infinite-loop-on-memcg-oom mm/memory.c
--- a/mm/memory.c~mm-thp-fix-infinite-loop-on-memcg-oom
+++ a/mm/memory.c
@@ -3704,7 +3704,6 @@ static int __handle_mm_fault(struct mm_s
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 @@ retry:
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;
}
}
_
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