From 9845cbbd113fbb5b769a45d8e88dc47bc12df4e0 Mon Sep 17 00:00:00 2001 From: Kirill A. Shutemov Date: Tue, 25 Feb 2014 15:01:42 -0800 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 Reported-by: Masayoshi Mizuma Reviewed-by: Michal Hocko Cc: Johannes Weiner Cc: Andrea Arcangeli Cc: David Rientjes Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/huge_memory.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) (limited to 'mm/huge_memory.c') diff --git a/mm/huge_memory.c b/mm/huge_memory.c index da23eb96779f..4df39b1bde91 100644 --- a/mm/huge_memory.c +++ b/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; } -- cgit v1.2.3-55-g7522