HWPOISON: Stop shrinking at right page count

When we call the slab shrinker to free a page we need to stop at
page count one because the caller always holds a single reference, not zero.

This avoids useless looping over slab shrinkers and freeing too much
memory.
Reviewed-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Andi Kleen <ak@linux.intel.com>

mm/memory-failure.c

@@ -235,7 +235,7 @@ void shake_page(struct page *p, int access)
 		int nr;
 		do {
 			nr = shrink_slab(1000, GFP_KERNEL, 1000);
-			if (page_count(p) == 0)
+			if (page_count(p) == 1)
 				break;
 		} while (nr > 10);
 	}