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Subject[PATCH 4.9 36/47] workqueue: avoid hard lockups in show_workqueue_state()
Date
4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

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();

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