From: Nick Piggin <npiggin@suse.de>

Add a bugcheck for Andrea's pagefault vs invalidate race.  This is triggerable
for both linear and nonlinear pages with a userspace test harness (using
direct IO and truncate, respectively).

Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/filemap.c |    1 +
 1 file changed, 1 insertion(+)

diff -puN mm/filemap.c~mm-debug-check-for-the-fault-vs-invalidate-race mm/filemap.c
--- a/mm/filemap.c~mm-debug-check-for-the-fault-vs-invalidate-race
+++ a/mm/filemap.c
@@ -120,6 +120,7 @@ void __remove_from_page_cache(struct pag
 	page->mapping = NULL;
 	mapping->nrpages--;
 	__dec_zone_page_state(page, NR_FILE_PAGES);
+	BUG_ON(page_mapped(page));
 }
 
 void remove_from_page_cache(struct page *page)
_