Patch "workqueue: avoid hard lockups in show_workqueue_state()" has been added to the 4.9-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    workqueue: avoid hard lockups in show_workqueue_state()

to the 4.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     workqueue-avoid-hard-lockups-in-show_workqueue_state.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>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: workqueue: avoid hard lockups in show_workqueue_state()

From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>

commit 62635ea8c18f0f62df4cc58379e4f1d33afd5801 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 kernel/workqueue.c |   13 +++++++++++++
 1 file changed, 13 insertions(+)

--- 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"
 
@@ -4424,6 +4425,12 @@ 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();
 		}
 	}
 
@@ -4451,6 +4458,12 @@ 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();


Patches currently in stable-queue which might be from sergey.senozhatsky.work@gmail.com are

queue-4.9/workqueue-avoid-hard-lockups-in-show_workqueue_state.patch