[PATCH] workqueue: add cmdline parameter workqueue.panic_on_watchdog/max_watchdog_to_panic

[Sangmoon Kim]

When we want to debug the workqueue stall, we can immediately make
a panic to get the information we want.

In some systems, it may be necessary to quickly reboot the system to
escape from a workqueue lockup situation. In this case, we can control
the number of stall detections to generate panic.

Signed-off-by: Sangmoon Kim <sangmoon.kim@xxxxxxxxxxx>
---
 kernel/workqueue.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index dfd42c28e404..893310ce23be 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -7406,6 +7406,11 @@ static struct timer_list wq_watchdog_timer;
 static unsigned long wq_watchdog_touched = INITIAL_JIFFIES;
 static DEFINE_PER_CPU(unsigned long, wq_watchdog_touched_cpu) = INITIAL_JIFFIES;
 
+static bool wq_panic_on_watchdog;
+module_param_named(panic_on_watchdog, wq_panic_on_watchdog, bool, 0644);
+static unsigned int wq_max_watchdog_to_panic;
+module_param_named(max_watchdog_to_panic, wq_max_watchdog_to_panic, uint, 0644);
+
 /*
  * Show workers that might prevent the processing of pending work items.
  * The only candidates are CPU-bound workers in the running state.
@@ -7457,6 +7462,16 @@ static void show_cpu_pools_hogs(void)
 	rcu_read_unlock();
 }
 
+static void panic_on_wq_watchdog(void)
+{
+	static unsigned int wq_busy;
+
+	if (wq_panic_on_watchdog) {
+		wq_busy++;
+		BUG_ON(wq_busy >= wq_max_watchdog_to_panic);
+	}
+}
+
 static void wq_watchdog_reset_touched(void)
 {
 	int cpu;
@@ -7529,6 +7544,9 @@ static void wq_watchdog_timer_fn(struct timer_list *unused)
 	if (cpu_pool_stall)
 		show_cpu_pools_hogs();
 
+	if (lockup_detected)
+		panic_on_wq_watchdog();
+
 	wq_watchdog_reset_touched();
 	mod_timer(&wq_watchdog_timer, jiffies + thresh);
 }
-- 
2.34.1