mm/hwpoison: fix race against poison thp
authorWanpeng Li <liwanp@linux.vnet.ibm.com>
Wed, 11 Sep 2013 21:22:53 +0000 (14:22 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Wed, 11 Sep 2013 22:58:08 +0000 (15:58 -0700)
commit0cea3fdc416d593072c602725ed2ca02b889f31b
tree11249ad6aa5e61fd8dbc42d277d733061f1b15e4
parentf9121153fdfbfaa930bf65077a5597e20d3ac608
mm/hwpoison: fix race against poison thp

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>
mm/memory-failure.c