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+

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 43d18cb46308385865d14ce40906c4646d378063..f699122dab321793bffa596da732d793d23d379b 100644 (file)
--- 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();