mm/memory-failure.c: fix memory leak by race between poison and unpoison

When a memory error happens on an in-use page or (free and in-use)
hugepage, the victim page is isolated with its refcount set to one.

When you try to unpoison it later, unpoison_memory() calls put_page()
for it twice in order to bring the page back to free page pool (buddy or
free hugepage list).  However, if another memory error occurs on the
page which we are unpoisoning, memory_failure() returns without
releasing the refcount which was incremented in the same call at first,
which results in memory leak and unconsistent num_poisoned_pages
statistics.  This patch fixes it.

Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: <stable@vger.kernel.org>    [2.6.32+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index dbf8922216ade6c88bbf1855cca60e881abc6b47..9ccef39a9de261c96f4e5775d7dca48b63d4d133 100644 (file)
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1153,6 +1153,8 @@ int memory_failure(unsigned long pfn, int trapno, int flags)
         */
        if (!PageHWPoison(p)) {
                printk(KERN_ERR "MCE %#lx: just unpoisoned\n", pfn);
+               atomic_long_sub(nr_pages, &num_poisoned_pages);
+               put_page(hpage);
                res = 0;
                goto out;
        }