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Date: Mon, 26 Aug 2013 16:46:07 +0800 From: Wanpeng Li <liwanp@...ux.vnet.ibm.com> To: Andrew Morton <akpm@...ux-foundation.org> Cc: Andi Kleen <andi@...stfloor.org>, Fengguang Wu <fengguang.wu@...el.com>, Naoya Horiguchi <n-horiguchi@...jp.nec.com>, Tony Luck <tony.luck@...el.com>, gong.chen@...ux.intel.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org, Wanpeng Li <liwanp@...ux.vnet.ibm.com> Subject: [PATCH v4 3/10] mm/hwpoison: fix race against poison thp v1 -> v2: * unpoison thp fail There is a race between hwpoison page and unpoison page, memory_failure set the page hwpoison and increase num_poisoned_pages without hold page lock, and one page count will be accounted against thp for num_poisoned_pages. However, unpoison can occur before memory_failure hold page lock and split transparent hugepage, unpoison will decrease num_poisoned_pages by 1 << compound_order since memory_failure has not yet split transparent hugepage with page lock held. That means we account one page for hwpoison and 1 << compound_order for unpoison. This patch fix it by inserting a PageTransHuge check before doing TestClearPageHWPoison, unpoison failed without clearing PageHWPoison and decreasing num_poisoned_pages. A B memory_failue TestSetPageHWPoison(p); if (PageHuge(p)) nr_pages = 1 << compound_order(hpage); else nr_pages = 1; atomic_long_add(nr_pages, &num_poisoned_pages); unpoison_memory nr_pages = 1<< compound_trans_order(page); if(TestClearPageHWPoison(p)) atomic_long_sub(nr_pages, &num_poisoned_pages); lock page if (!PageHWPoison(p)) unlock page and return hwpoison_user_mappings if (PageTransHuge(hpage)) split_huge_page(hpage); Suggested-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com> Signed-off-by: Wanpeng Li <liwanp@...ux.vnet.ibm.com> --- mm/memory-failure.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/mm/memory-failure.c b/mm/memory-failure.c index 5a4f4d6..a6c4752 100644 --- a/mm/memory-failure.c +++ b/mm/memory-failure.c @@ -1339,6 +1339,16 @@ int unpoison_memory(unsigned long pfn) return 0; } + /* + * unpoison_memory() can encounter thp only when the thp is being + * worked by memory_failure() and the page lock is not held yet. + * In such case, we yield to memory_failure() and make unpoison fail. + */ + if (PageTransHuge(page)) { + pr_info("MCE: Memory failure is now running on %#lx\n", pfn); + return 0; + } + nr_pages = 1 << compound_order(page); if (!get_page_unless_zero(page)) { -- 1.8.1.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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