rcu: Use wrapper function instead of exporting tasklist_lock

Lockdep-RCU commit d11c563d exported tasklist_lock, which is not
a good thing.  This patch instead exports a function that uses
lockdep to check whether tasklist_lock is held.

Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
Cc: Christoph Hellwig <hch@lst.de>
LKML-Reference: <1267631219-8713-1-git-send-email-paulmck@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/exit.c b/kernel/exit.c
index 45ed043..fed3a4d 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -87,7 +87,7 @@
 
 	sighand = rcu_dereference_check(tsk->sighand,
 					rcu_read_lock_held() ||
-					lockdep_is_held(&tasklist_lock));
+					lockdep_tasklist_lock_is_held());
 	spin_lock(&sighand->siglock);
 
 	posix_cpu_timers_exit(tsk);