From: Nick Piggin <npiggin@suse.de>

As per the comment here, we can only use that shortcut if rcu_read_lock
disabled preemption.  It would be somewhat annoying to have to put
preempt_disable/preempt_enable around all callers in order to support
this, but preempt RCU isn't going to be hugely performance critical
anyway (and actually it actively trades performance for fewer preempt
off sections), so it can use the slightly slower path quite happily.

Cc: Jeff Garzik <jeff@garzik.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Hugh Dickins <hugh@veritas.com>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/pagemap.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff -puN include/linux/pagemap.h~mm-speculative-page-references-fix include/linux/pagemap.h
--- a/include/linux/pagemap.h~mm-speculative-page-references-fix
+++ a/include/linux/pagemap.h
@@ -111,7 +111,7 @@ static inline int page_cache_get_specula
 {
 	VM_BUG_ON(in_interrupt());
 
-#ifndef CONFIG_SMP
+#if !defined(CONFIG_SMP) && defined(CONFIG_CLASSIC_RCU)
 # ifdef CONFIG_PREEMPT
 	VM_BUG_ON(!in_atomic());
 # endif
_