Allow CONFIG_DEBUG_VM to switch off the prefaulting logic, to simulate the
difficult race where the page may be unmapped before calling copy_from_user.
Makes the race much easier to hit.
This is useful for demonstration and testing purposes, but is removed in a
subsequent patch.
Signed-off-by: Nick Piggin <npiggin@xxxxxxx>
Index: linux-2.6/mm/filemap.c
===================================================================
--- linux-2.6.orig/mm/filemap.c
+++ linux-2.6/mm/filemap.c
@@ -1894,6 +1894,7 @@ generic_file_buffered_write(struct kiocb
if (maxlen > bytes)
maxlen = bytes;
+#ifndef CONFIG_DEBUG_VM
/*
* Bring in the user page that we will copy from _first_.
* Otherwise there's a nasty deadlock on copying from the
@@ -1901,6 +1902,7 @@ generic_file_buffered_write(struct kiocb
* up-to-date.
*/
fault_in_pages_readable(buf, maxlen);
+#endif
page = __grab_cache_page(mapping,index,&cached_page,&lru_pvec);
if (!page) {
-
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