[patch 1/7] mm: debug check for the fault vs invalidate race

[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>

Index: linux-2.6/mm/filemap.c
===================================================================
--- linux-2.6.orig/mm/filemap.c
+++ linux-2.6/mm/filemap.c
@@ -120,6 +120,8 @@ 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)
-
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