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 <[e-mail]>
Acked-by: Roland McGrath <[e-mail]>
Cc: Steven Rostedt <[e-mail]>
Cc: Andrew Morton <[e-mail]>
Cc: Jason Baron <[e-mail]>
Cc: Masami Hiramatsu <[e-mail]>
Cc: 2.6.33.x-2.6.34.x <[e-mail]>
LKML-Reference: <[e-mail]>
Signed-off-by: Frederic Weisbecker <[e-mail]>

include/trace/events/signal.h

···
 
 #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) {		\