signal: turn dequeue_signal_lock() into kernel_dequeue_signal()

1. Rename dequeue_signal_lock() to kernel_dequeue_signal(). This
   matches another "for kthreads only" kernel_sigaction() helper.

2. Remove the "tsk" and "mask" arguments, they are always current
   and current->blocked. And it is simply wrong if tsk != current.

3. We could also remove the 3rd "siginfo_t *info" arg but it looks
   potentially useful. However we can simplify the callers if we
   change kernel_dequeue_signal() to accept info => NULL.

4. Remove _irqsave, it is never called from atomic context.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Tejun Heo <tj@kernel.org>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Felipe Balbi <balbi@ti.com>
Cc: Markus Pargmann <mpa@pengutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/block/nbd.c

@@ -444,9 +444,7 @@ static int nbd_thread_recv(struct nbd_device *nbd)
 	spin_unlock_irqrestore(&nbd->tasks_lock, flags);
 
 	if (signal_pending(current)) {
-		siginfo_t info;
+		ret = kernel_dequeue_signal(NULL);
-
-		ret = dequeue_signal_lock(current, &current->blocked, &info);
 		dev_warn(nbd_to_dev(nbd), "pid %d, %s, got signal %d\n",
 			 task_pid_nr(current), current->comm, ret);
 		mutex_lock(&nbd->tx_lock);
@@ -560,11 +558,8 @@ static int nbd_thread_send(void *data)
 					 !list_empty(&nbd->waiting_queue));
 
 		if (signal_pending(current)) {
-			siginfo_t info;
+			int ret = kernel_dequeue_signal(NULL);
-			int ret;
 
-			ret = dequeue_signal_lock(current, &current->blocked,
-						  &info);
 			dev_warn(nbd_to_dev(nbd), "pid %d, %s, got signal %d\n",
 				 task_pid_nr(current), current->comm, ret);
 			mutex_lock(&nbd->tx_lock);
@@ -592,10 +587,8 @@ static int nbd_thread_send(void *data)
 	spin_unlock_irqrestore(&nbd->tasks_lock, flags);
 
 	/* Clear maybe pending signals */
-	if (signal_pending(current)) {
+	if (signal_pending(current))
-		siginfo_t info;
+		kernel_dequeue_signal(NULL);
-		dequeue_signal_lock(current, &current->blocked, &info);
-	}
 
 	return 0;
 }

drivers/usb/gadget/function/f_mass_storage.c

@@ -2345,7 +2345,6 @@ static void fsg_disable(struct usb_function *f)
 
 static void handle_exception(struct fsg_common *common)
 {
-	siginfo_t		info;
 	int			i;
 	struct fsg_buffhd	*bh;
 	enum fsg_state		old_state;
@@ -2357,8 +2356,7 @@ static void handle_exception(struct fsg_common *common)
 	 * into a high-priority EXIT exception.
 	 */
 	for (;;) {
-		int sig =
+		int sig = kernel_dequeue_signal(NULL);
-			dequeue_signal_lock(current, &current->blocked, &info);
 		if (!sig)
 			break;
 		if (sig != SIGUSR1) {

fs/jffs2/background.c

@@ -121,13 +121,12 @@ static int jffs2_garbage_collect_thread(void *_c)
 		/* Put_super will send a SIGKILL and then wait on the sem.
 		 */
 		while (signal_pending(current) || freezing(current)) {
-			siginfo_t info;
 			unsigned long signr;
 
 			if (try_to_freeze())
 				goto again;
 
-			signr = dequeue_signal_lock(current, &current->blocked, &info);
+			signr = kernel_dequeue_signal(NULL);
 
 			switch(signr) {
 			case SIGSTOP:

include/linux/sched.h

@@ -2462,14 +2462,15 @@ 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 *tsk, sigset_t *mask, siginfo_t *info);
 
-static inline int dequeue_signal_lock(struct task_struct *tsk, sigset_t *mask, siginfo_t *info)
+static inline int kernel_dequeue_signal(siginfo_t *info)
 {
-	unsigned long flags;
+	struct task_struct *tsk = current;
+	siginfo_t __info;
 	int ret;
 
-	spin_lock_irqsave(&tsk->sighand->siglock, flags);
+	spin_lock_irq(&tsk->sighand->siglock);
-	ret = dequeue_signal(tsk, mask, info);
+	ret = dequeue_signal(tsk, &tsk->blocked, info ?: &__info);
-	spin_unlock_irqrestore(&tsk->sighand->siglock, flags);
+	spin_unlock_irq(&tsk->sighand->siglock);
 
 	return ret;
 }