tracing: Fix null pointer deref with SEND_SIG_FORCED

BUG: unable to handle kernel NULL pointer dereference at
	0000000000000006
IP: [<ffffffff8107bd37>] ftrace_raw_event_signal_generate+0x87/0x140

TP_STORE_SIGINFO() forgets about SEND_SIG_FORCED, fix.

We should probably export is_si_special() and change TP_STORE_SIGINFO()
to use it in the longer term.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Roland McGrath <roland@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jason Baron <jbaron@redhat.com>
Cc: Masami Hiramatsu <mhiramat@redhat.com>
Cc: 2.6.33.x-2.6.34.x <stable@kernel.org>
LKML-Reference: <20100603213409.GA8307@redhat.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>

include/trace/events/signal.h

@@ -10,7 +10,8 @@
 
 #define TP_STORE_SIGINFO(__entry, info)				\
 	do {							\
-		if (info == SEND_SIG_NOINFO) {			\
+		if (info == SEND_SIG_NOINFO ||			\
+		    info == SEND_SIG_FORCED) {			\
 			__entry->errno	= 0;			\
 			__entry->code	= SI_USER;		\
 		} else if (info == SEND_SIG_PRIV) {		\