signals: cleanup the usage of t/current in do_sigaction()

The usage of "task_struct *t" and "current" in do_sigaction() looks really
annoying and chaotic.  Initially "t" is used as a cached value of current
but not consistently, then it is reused as a loop variable and we have to
use "current" again.

Clean up this mess and also convert the code to use for_each_thread().

Signed-off-by: Oleg Nesterov <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Al Viro <[email protected]>
Cc: David Woodhouse <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Cc: Geert Uytterhoeven <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Mathieu Desnoyers <[email protected]>
Cc: Richard Weinberger <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Tejun Heo <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

kernel/signal.c

@@ -3068,16 +3068,16 @@ COMPAT_SYSCALL_DEFINE4(rt_tgsigqueueinfo,
 
 int do_sigaction(int sig, struct k_sigaction *act, struct k_sigaction *oact)
 {
-	struct task_struct *t = current;
+	struct task_struct *p = current, *t;
 	struct k_sigaction *k;
 	sigset_t mask;
 
 	if (!valid_signal(sig) || sig < 1 || (act && sig_kernel_only(sig)))
 		return -EINVAL;
 
-	k = &t->sighand->action[sig-1];
+	k = &p->sighand->action[sig-1];
 
-	spin_lock_irq(&current->sighand->siglock);
+	spin_lock_irq(&p->sighand->siglock);
 	if (oact)
 		*oact = *k;
 
@@ -3096,17 +3096,16 @@ int do_sigaction(int sig, struct k_sigaction *act, struct k_sigaction *oact)
 		 *   (for example, SIGCHLD), shall cause the pending signal to
 		 *   be discarded, whether or not it is blocked"
 		 */
-		if (sig_handler_ignored(sig_handler(t, sig), sig)) {
+		if (sig_handler_ignored(sig_handler(p, sig), sig)) {
 			sigemptyset(&mask);
 			sigaddset(&mask, sig);
-			flush_sigqueue_mask(&mask, &t->signal->shared_pending);
-			do {
+			flush_sigqueue_mask(&mask, &p->signal->shared_pending);
+			for_each_thread(p, t)
 				flush_sigqueue_mask(&mask, &t->pending);
-			} while_each_thread(current, t);
 		}
 	}
 
-	spin_unlock_irq(&current->sighand->siglock);
+	spin_unlock_irq(&p->sighand->siglock);
 	return 0;
 }