Add SIGSTOP and SIGTSTP handling to issig

This change adds SIGSTOP and SIGTSTP handling to the issig function; 
this mirrors its behavior on Solaris. This way, long running kernel 
tasks can be stopped with the appropriate signals. Note that doing 
so with ctrl-z on the command line doesn't return control of the tty 
to the shell, because tty handling is done separately from stopping 
the process. That can be future work, if people feel that it is a 
necessary addition.

Reviewed-by: Brian Behlendorf <[email protected]>
Reviewed-by: Matthew Ahrens <[email protected]>
Signed-off-by: Paul Dagnelie <[email protected]>
Issue #810 
Issue #10843 
Closes #11801 

1 files changed, 51 insertions, 0 deletions

diff --git a/module/os/linux/spl/spl-thread.c b/module/os/linux/spl/spl-thread.c
index db23fb64a..834c52711 100644
--- a/module/os/linux/spl/spl-thread.c
+++ b/module/os/linux/spl/spl-thread.c
@@ -158,3 +158,54 @@ spl_kthread_create(int (*func)(void *), void *data, const char namefmt[], ...)
 	} while (1);
 }
 EXPORT_SYMBOL(spl_kthread_create);
+
+/*
+ * The "why" argument indicates the allowable side-effects of the call:
+ *
+ * FORREAL:  Extract the next pending signal from p_sig into p_cursig;
+ * stop the process if a stop has been requested or if a traced signal
+ * is pending.
+ *
+ * JUSTLOOKING:  Don't stop the process, just indicate whether or not
+ * a signal might be pending (FORREAL is needed to tell for sure).
+ */
+int
+issig(int why)
+{
+	ASSERT(why == FORREAL || why == JUSTLOOKING);
+
+	if (!signal_pending(current))
+		return (0);
+
+	if (why != FORREAL)
+		return (1);
+
+	struct task_struct *task = current;
+	spl_kernel_siginfo_t __info;
+	sigset_t set;
+	siginitsetinv(&set, 1ULL << (SIGSTOP - 1) | 1ULL << (SIGTSTP - 1));
+	sigorsets(&set, &task->blocked, &set);
+
+	spin_lock_irq(&task->sighand->siglock);
+	int ret;
+	if ((ret = dequeue_signal(task, &set, &__info)) != 0) {
+#ifdef HAVE_SIGNAL_STOP
+		spin_unlock_irq(&task->sighand->siglock);
+		kernel_signal_stop();
+#else
+		if (current->jobctl & JOBCTL_STOP_DEQUEUED)
+			spl_set_special_state(TASK_STOPPED);
+
+		spin_unlock_irq(&current->sighand->siglock);
+
+		schedule();
+#endif
+		return (0);
+	}
+
+	spin_unlock_irq(&task->sighand->siglock);
+
+	return (1);
+}
+
+EXPORT_SYMBOL(issig);