6 files changed, 83 insertions, 57 deletions

diff --git a/drivers/s390/char/con3215.c b/drivers/s390/char/con3215.c
index f356607835d8..4ae07c7e2175 100644
--- a/drivers/s390/char/con3215.c
+++ b/drivers/s390/char/con3215.c
@@ -771,35 +771,36 @@ static struct tty_driver *con3215_device(struct console *c, int *index)
 }
 
 /*
- * panic() calls con3215_flush through a panic_notifier
- * before the system enters a disabled, endless loop.
+ * The below function is called as a panic/reboot notifier before the
+ * system enters a disabled, endless loop.
+ *
+ * Notice we must use the spin_trylock() alternative, to prevent lockups
+ * in atomic context (panic routine runs with secondary CPUs, local IRQs
+ * and preemption disabled).
  */
-static void con3215_flush(void)
+static int con3215_notify(struct notifier_block *self,
+			  unsigned long event, void *data)
 {
 	struct raw3215_info *raw;
 	unsigned long flags;
 
 	raw = raw3215[0];  /* console 3215 is the first one */
-	spin_lock_irqsave(get_ccwdev_lock(raw->cdev), flags);
+	if (!spin_trylock_irqsave(get_ccwdev_lock(raw->cdev), flags))
+		return NOTIFY_DONE;
 	raw3215_make_room(raw, RAW3215_BUFFER_SIZE);
 	spin_unlock_irqrestore(get_ccwdev_lock(raw->cdev), flags);
-}
 
-static int con3215_notify(struct notifier_block *self,
-			  unsigned long event, void *data)
-{
-	con3215_flush();
-	return NOTIFY_OK;
+	return NOTIFY_DONE;
 }
 
 static struct notifier_block on_panic_nb = {
 	.notifier_call = con3215_notify,
-	.priority = 0,
+	.priority = INT_MIN + 1, /* run the callback late */
 };
 
 static struct notifier_block on_reboot_nb = {
 	.notifier_call = con3215_notify,
-	.priority = 0,
+	.priority = INT_MIN + 1, /* run the callback late */
 };
 
 /*
diff --git a/drivers/s390/char/con3270.c b/drivers/s390/char/con3270.c
index e4592890f20a..10f6a37fb153 100644
--- a/drivers/s390/char/con3270.c
+++ b/drivers/s390/char/con3270.c
@@ -535,20 +535,26 @@ con3270_wait_write(struct con3270 *cp)
 }
 
 /*
- * panic() calls con3270_flush through a panic_notifier
- * before the system enters a disabled, endless loop.
+ * The below function is called as a panic/reboot notifier before the
+ * system enters a disabled, endless loop.
+ *
+ * Notice we must use the spin_trylock() alternative, to prevent lockups
+ * in atomic context (panic routine runs with secondary CPUs, local IRQs
+ * and preemption disabled).
  */
-static void
-con3270_flush(void)
+static int con3270_notify(struct notifier_block *self,
+			  unsigned long event, void *data)
 {
 	struct con3270 *cp;
 	unsigned long flags;
 
 	cp = condev;
 	if (!cp->view.dev)
-		return;
-	raw3270_activate_view(&cp->view);
-	spin_lock_irqsave(&cp->view.lock, flags);
+		return NOTIFY_DONE;
+	if (!raw3270_view_lock_unavailable(&cp->view))
+		raw3270_activate_view(&cp->view);
+	if (!spin_trylock_irqsave(&cp->view.lock, flags))
+		return NOTIFY_DONE;
 	con3270_wait_write(cp);
 	cp->nr_up = 0;
 	con3270_rebuild_update(cp);
@@ -560,23 +566,18 @@ con3270_flush(void)
 		con3270_wait_write(cp);
 	}
 	spin_unlock_irqrestore(&cp->view.lock, flags);
-}
 
-static int con3270_notify(struct notifier_block *self,
-			  unsigned long event, void *data)
-{
-	con3270_flush();
-	return NOTIFY_OK;
+	return NOTIFY_DONE;
 }
 
 static struct notifier_block on_panic_nb = {
 	.notifier_call = con3270_notify,
-	.priority = 0,
+	.priority = INT_MIN + 1, /* run the callback late */
 };
 
 static struct notifier_block on_reboot_nb = {
 	.notifier_call = con3270_notify,
-	.priority = 0,
+	.priority = INT_MIN + 1, /* run the callback late */
 };
 
 /*
diff --git a/drivers/s390/char/raw3270.c b/drivers/s390/char/raw3270.c
index dfde0d941c3c..4e2b3a1a3b2e 100644
--- a/drivers/s390/char/raw3270.c
+++ b/drivers/s390/char/raw3270.c
@@ -831,6 +831,21 @@ raw3270_create_device(struct ccw_device *cdev)
 }
 
 /*
+ * This helper just validates that it is safe to activate a
+ * view in the panic() context, due to locking restrictions.
+ */
+int raw3270_view_lock_unavailable(struct raw3270_view *view)
+{
+	struct raw3270 *rp = view->dev;
+
+	if (!rp)
+		return -ENODEV;
+	if (spin_is_locked(get_ccwdev_lock(rp->cdev)))
+		return -EBUSY;
+	return 0;
+}
+
+/*
  * Activate a view.
  */
 int
diff --git a/drivers/s390/char/raw3270.h b/drivers/s390/char/raw3270.h
index c6645167cd2b..4cb6b5ee44ca 100644
--- a/drivers/s390/char/raw3270.h
+++ b/drivers/s390/char/raw3270.h
@@ -160,6 +160,7 @@ struct raw3270_view {
 };
 
 int raw3270_add_view(struct raw3270_view *, struct raw3270_fn *, int, int);
+int raw3270_view_lock_unavailable(struct raw3270_view *view);
 int raw3270_activate_view(struct raw3270_view *);
 void raw3270_del_view(struct raw3270_view *);
 void raw3270_deactivate_view(struct raw3270_view *);
diff --git a/drivers/s390/char/sclp_con.c b/drivers/s390/char/sclp_con.c
index fe5ee2646fcf..e5d947c763ea 100644
--- a/drivers/s390/char/sclp_con.c
+++ b/drivers/s390/char/sclp_con.c
@@ -220,30 +220,34 @@ sclp_console_device(struct console *c, int *index)
 }
 
 /*
- * Make sure that all buffers will be flushed to the SCLP.
+ * This panic/reboot notifier makes sure that all buffers
+ * will be flushed to the SCLP.
  */
-static void
-sclp_console_flush(void)
+static int sclp_console_notify(struct notifier_block *self,
+			       unsigned long event, void *data)
 {
+	/*
+	 * Perform the lock check before effectively getting the
+	 * lock on sclp_conbuf_emit() / sclp_console_sync_queue()
+	 * to prevent potential lockups in atomic context.
+	 */
+	if (spin_is_locked(&sclp_con_lock))
+		return NOTIFY_DONE;
+
 	sclp_conbuf_emit();
 	sclp_console_sync_queue();
-}
 
-static int sclp_console_notify(struct notifier_block *self,
-			       unsigned long event, void *data)
-{
-	sclp_console_flush();
-	return NOTIFY_OK;
+	return NOTIFY_DONE;
 }
 
 static struct notifier_block on_panic_nb = {
 	.notifier_call = sclp_console_notify,
-	.priority = 1,
+	.priority = INT_MIN + 1, /* run the callback late */
 };
 
 static struct notifier_block on_reboot_nb = {
 	.notifier_call = sclp_console_notify,
-	.priority = 1,
+	.priority = INT_MIN + 1, /* run the callback late */
 };
 
 /*
diff --git a/drivers/s390/char/sclp_vt220.c b/drivers/s390/char/sclp_vt220.c
index 3b4e7e5d9b71..a32f34a1c6d2 100644
--- a/drivers/s390/char/sclp_vt220.c
+++ b/drivers/s390/char/sclp_vt220.c
@@ -769,21 +769,6 @@ __initcall(sclp_vt220_tty_init);
 
 #ifdef CONFIG_SCLP_VT220_CONSOLE
 
-static void __sclp_vt220_flush_buffer(void)
-{
-	unsigned long flags;
-
-	sclp_vt220_emit_current();
-	spin_lock_irqsave(&sclp_vt220_lock, flags);
-	del_timer(&sclp_vt220_timer);
-	while (sclp_vt220_queue_running) {
-		spin_unlock_irqrestore(&sclp_vt220_lock, flags);
-		sclp_sync_wait();
-		spin_lock_irqsave(&sclp_vt220_lock, flags);
-	}
-	spin_unlock_irqrestore(&sclp_vt220_lock, flags);
-}
-
 static void
 sclp_vt220_con_write(struct console *con, const char *buf, unsigned int count)
 {
@@ -797,22 +782,41 @@ sclp_vt220_con_device(struct console *c, int *index)
 	return sclp_vt220_driver;
 }
 
+/*
+ * This panic/reboot notifier runs in atomic context, so
+ * locking restrictions apply to prevent potential lockups.
+ */
 static int
 sclp_vt220_notify(struct notifier_block *self,
 			  unsigned long event, void *data)
 {
-	__sclp_vt220_flush_buffer();
-	return NOTIFY_OK;
+	unsigned long flags;
+
+	if (spin_is_locked(&sclp_vt220_lock))
+		return NOTIFY_DONE;
+
+	sclp_vt220_emit_current();
+
+	spin_lock_irqsave(&sclp_vt220_lock, flags);
+	del_timer(&sclp_vt220_timer);
+	while (sclp_vt220_queue_running) {
+		spin_unlock_irqrestore(&sclp_vt220_lock, flags);
+		sclp_sync_wait();
+		spin_lock_irqsave(&sclp_vt220_lock, flags);
+	}
+	spin_unlock_irqrestore(&sclp_vt220_lock, flags);
+
+	return NOTIFY_DONE;
 }
 
 static struct notifier_block on_panic_nb = {
 	.notifier_call = sclp_vt220_notify,
-	.priority = 1,
+	.priority = INT_MIN + 1, /* run the callback late */
 };
 
 static struct notifier_block on_reboot_nb = {
 	.notifier_call = sclp_vt220_notify,
-	.priority = 1,
+	.priority = INT_MIN + 1, /* run the callback late */
 };
 
 /* Structure needed to register with printk */