From 62635ea8c18f0f62df4cc58379e4f1d33afd5801 Mon Sep 17 00:00:00 2001
From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Date: Thu, 11 Jan 2018 09:53:35 +0900
Subject: [PATCH] workqueue: avoid hard lockups in show_workqueue_state()

References: bsc#1085474
Patch-mainline: v4.15-rc9
Git-commit: 62635ea8c18f0f62df4cc58379e4f1d33afd5801

show_workqueue_state() can print out a lot of messages while being in
atomic context, e.g. sysrq-t -> show_workqueue_state(). If the console
device is slow it may end up triggering NMI hard lockup watchdog.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: stable@vger.kernel.org # v4.5+
Acked-by: Michal Suchanek <msuchanek@suse.de>
---
 kernel/workqueue.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index f48983413342..a52543506037 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -48,6 +48,7 @@
 #include <linux/nodemask.h>
 #include <linux/moduleparam.h>
 #include <linux/uaccess.h>
+#include <linux/nmi.h>
 
 #include "workqueue_internal.h"
 
@@ -4439,6 +4440,12 @@ void show_workqueue_state(void)
 			if (pwq->nr_active || !list_empty(&pwq->delayed_works))
 				show_pwq(pwq);
 			spin_unlock_irqrestore(&pwq->pool->lock, flags);
+			/*
+			 * We could be printing a lot from atomic context, e.g.
+			 * sysrq-t -> show_workqueue_state(). Avoid triggering
+			 * hard lockup.
+			 */
+			touch_nmi_watchdog();
 		}
 	}
 
@@ -4466,6 +4473,12 @@ void show_workqueue_state(void)
 		pr_cont("\n");
 	next_pool:
 		spin_unlock_irqrestore(&pool->lock, flags);
+		/*
+		 * We could be printing a lot from atomic context, e.g.
+		 * sysrq-t -> show_workqueue_state(). Avoid triggering
+		 * hard lockup.
+		 */
+		touch_nmi_watchdog();
 	}
 
 	rcu_read_unlock_sched();
-- 
2.13.6