[PATCH] hrtimers: fixup itimer conversion

The itimer conversion removed the locking which protects the timer and
variables in the shared signal structure.  Steven Rostedt found the problem in
the latest -rt patches.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

kernel/itimer.c

@@ -49,9 +49,11 @@ int do_getitimer(int which, struct itimerval *value)
 
 	switch (which) {
 	case ITIMER_REAL:
+		spin_lock_irq(&tsk->sighand->siglock);
 		value->it_value = itimer_get_remtime(&tsk->signal->real_timer);
 		value->it_interval =
 			ktime_to_timeval(tsk->signal->it_real_incr);
+		spin_unlock_irq(&tsk->sighand->siglock);
 		break;
 	case ITIMER_VIRTUAL:
 		read_lock(&tasklist_lock);
@@ -150,8 +152,14 @@ int do_setitimer(int which, struct itimerval *value, struct itimerval *ovalue)
 
 	switch (which) {
 	case ITIMER_REAL:
+again:
+		spin_lock_irq(&tsk->sighand->siglock);
 		timer = &tsk->signal->real_timer;
-		hrtimer_cancel(timer);
+		/* We are sharing ->siglock with it_real_fn() */
+		if (hrtimer_try_to_cancel(timer) < 0) {
+			spin_unlock_irq(&tsk->sighand->siglock);
+			goto again;
+		}
 		if (ovalue) {
 			ovalue->it_value = itimer_get_remtime(timer);
 			ovalue->it_interval
@@ -162,6 +170,7 @@ int do_setitimer(int which, struct itimerval *value, struct itimerval *ovalue)
 		expires = timeval_to_ktime(value->it_value);
 		if (expires.tv64 != 0)
 			hrtimer_start(timer, expires, HRTIMER_REL);
+		spin_unlock_irq(&tsk->sighand->siglock);
 		break;
 	case ITIMER_VIRTUAL:
 		nval = timeval_to_cputime(&value->it_value);