workqueue: avoid hard lockups in show_workqueue_state()

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+

1 files changed, 13 insertions, 0 deletions

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 43d18cb46308..f699122dab32 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -48,6 +48,7 @@
 #include <linux/moduleparam.h>
 #include <linux/uaccess.h>
 #include <linux/sched/isolation.h>
+#include <linux/nmi.h>
 
 #include "workqueue_internal.h"
 
@@ -4463,6 +4464,12 @@ 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();
                 }
         }
 
@@ -4490,6 +4497,12 @@ 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();