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mm/hwpoison: fix race against poison thp

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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);

Signed-off-by: Wanpeng Li <liwanp@linux.vnet.ibm.com>
Suggested-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Tony Luck <tony.luck@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Wanpeng Li 2013-09-11 14:22:53 -07:00 committed by Linus Torvalds
parent f9121153fd
commit 0cea3fdc41
1 changed files with 10 additions and 0 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

10
mm/memory-failure.c
View file

@ -1342,6 +1342,16 @@ 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)) {