kpagecount: add slab page checking because _mapcount is in a union

Add a PageSlab() check before adding the _mapcount value to /kpagecount.
page->_mapcount is in a union with the SLAB structure so for pages
controlled by SLAB, page_mapcount() returns nonsense.

Signed-off-by: Petr Holasek <pholasek@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Matt Mackall <mpm@selenic.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/proc/page.c b/fs/proc/page.c
index 3b8b456603318f1ff017056cdeda40129d559ab4..b06c674624e6af3691cbe00d51c7b1a2b5aa7a8a 100644 (file)
--- a/fs/proc/page.c
+++ b/fs/proc/page.c
@@ -40,7 +40,7 @@ static ssize_t kpagecount_read(struct file *file, char __user *buf,
                        ppage = pfn_to_page(pfn);
                else
                        ppage = NULL;
-               if (!ppage)
+               if (!ppage || PageSlab(ppage))
                        pcount = 0;
                else
                        pcount = page_mapcount(ppage);