signal: Remove task argument from dequeue_signal()

The task pointer which is handed to dequeue_signal() is always current. The
argument along with the first comment about signalfd in that function is
confusing at best. Remove it and use current internally.

Update the stale comment for dequeue_signal() while at it.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

fs/signalfd.c

@@ -159,7 +159,7 @@ static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, kernel_siginfo_t *info
 	DECLARE_WAITQUEUE(wait, current);
 
 	spin_lock_irq(&current->sighand->siglock);
-	ret = dequeue_signal(current, &ctx->sigmask, info, &type);
+	ret = dequeue_signal(&ctx->sigmask, info, &type);
 	switch (ret) {
 	case 0:
 		if (!nonblock)
@@ -174,7 +174,7 @@ static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, kernel_siginfo_t *info
 	add_wait_queue(&current->sighand->signalfd_wqh, &wait);
 	for (;;) {
 		set_current_state(TASK_INTERRUPTIBLE);
-		ret = dequeue_signal(current, &ctx->sigmask, info, &type);
+		ret = dequeue_signal(&ctx->sigmask, info, &type);
 		if (ret != 0)
 			break;
 		if (signal_pending(current)) {

include/linux/sched/signal.h

@@ -276,8 +276,7 @@ static inline void signal_set_stop_flags(struct signal_struct *sig,
 extern void flush_signals(struct task_struct *);
 extern void ignore_signals(struct task_struct *);
 extern void flush_signal_handlers(struct task_struct *, int force_default);
-extern int dequeue_signal(struct task_struct *task, sigset_t *mask,
-			  kernel_siginfo_t *info, enum pid_type *type);
+extern int dequeue_signal(sigset_t *mask, kernel_siginfo_t *info, enum pid_type *type);
 
 static inline int kernel_dequeue_signal(void)
 {
@@ -287,7 +286,7 @@ static inline int kernel_dequeue_signal(void)
 	int ret;
 
 	spin_lock_irq(&task->sighand->siglock);
-	ret = dequeue_signal(task, &task->blocked, &__info, &__type);
+	ret = dequeue_signal(&task->blocked, &__info, &__type);
 	spin_unlock_irq(&task->sighand->siglock);
 
 	return ret;

kernel/signal.c

@@ -618,20 +618,18 @@ static int __dequeue_signal(struct sigpending *pending, sigset_t *mask,
 }
 
 /*
- * Dequeue a signal and return the element to the caller, which is
- * expected to free it.
- *
- * All callers have to hold the siglock.
+ * Try to dequeue a signal. If a deliverable signal is found fill in the
+ * caller provided siginfo and return the signal number. Otherwise return
+ * 0.
  */
-int dequeue_signal(struct task_struct *tsk, sigset_t *mask,
-		   kernel_siginfo_t *info, enum pid_type *type)
+int dequeue_signal(sigset_t *mask, kernel_siginfo_t *info, enum pid_type *type)
 {
+	struct task_struct *tsk = current;
 	bool resched_timer = false;
 	int signr;
 
-	/* We only dequeue private signals from ourselves, we don't let
-	 * signalfd steal them
-	 */
+	lockdep_assert_held(&tsk->sighand->siglock);
+
 	*type = PIDTYPE_PID;
 	signr = __dequeue_signal(&tsk->pending, mask, info, &resched_timer);
 	if (!signr) {
@@ -2793,8 +2791,7 @@ bool get_signal(struct ksignal *ksig)
 		type = PIDTYPE_PID;
 		signr = dequeue_synchronous_signal(&ksig->info);
 		if (!signr)
-			signr = dequeue_signal(current, &current->blocked,
-					       &ksig->info, &type);
+			signr = dequeue_signal(&current->blocked, &ksig->info, &type);
 
 		if (!signr)
 			break; /* will return 0 */
@@ -3648,7 +3645,7 @@ static int do_sigtimedwait(const sigset_t *which, kernel_siginfo_t *info,
 	signotset(&mask);
 
 	spin_lock_irq(&tsk->sighand->siglock);
-	sig = dequeue_signal(tsk, &mask, info, &type);
+	sig = dequeue_signal(&mask, info, &type);
 	if (!sig && timeout) {
 		/*
 		 * None ready, temporarily unblock those we're interested
@@ -3667,7 +3664,7 @@ static int do_sigtimedwait(const sigset_t *which, kernel_siginfo_t *info,
 		spin_lock_irq(&tsk->sighand->siglock);
 		__set_task_blocked(tsk, &tsk->real_blocked);
 		sigemptyset(&tsk->real_blocked);
-		sig = dequeue_signal(tsk, &mask, info, &type);
+		sig = dequeue_signal(&mask, info, &type);
 	}
 	spin_unlock_irq(&tsk->sighand->siglock);