workqueue: Fix hung time report of worker pools

The workqueue watchdog prints a warning when there is no progress in a worker pool. Where the progress means that the pool started processing a pending work item. Note that it is perfectly fine to process work items much longer. The progress should be guaranteed by waking up or creating idle workers. show_one_worker_pool() prints state of non-idle worker pool. It shows a delay since the last pool->watchdog_ts. The timestamp is updated when a first pending work is queued in __queue_work(). Also it is updated when a work is dequeued for processing in worker_thread() and rescuer_thread(). The delay is misleading when there is no pending work item. In this case it shows how long the last work item is being proceed. Show zero instead. There is no stall if there is no pending work.

Petr Mladek committed 3 years ago

Commit 335a42e1 parent a8ec5881 file · +7 −3Browse files

Showing the changes to kernel/workqueue.c (1 of 1 file). Show all

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kernel/workqueue.c+7−3

@@ -5000,10 +5000,16 @@ static void show_one_worker_pool(struct worker_pool *pool) · 4999 unmodified lines
5000	5000	struct worker *worker;
5001	5001	bool first = true;
5002	5002	unsigned long flags;
	5003	+ unsigned long hung = 0;
5003	5004
5004	5005	raw_spin_lock_irqsave(&pool->lock, flags);
5005	5006	if (pool->nr_workers == pool->nr_idle)
5006	5007	goto next_pool;
	5008	+
	5009	+ /* How long the first pending work is waiting for a worker. */
	5010	+ if (!list_empty(&pool->worklist))
	5011	+ hung = jiffies_to_msecs(jiffies - pool->watchdog_ts) / 1000;
	5012	+
5007	5013	/*
5008	5014	* Defer printing to avoid deadlocks in console drivers that
5009	5015	* queue work while holding locks also taken in their write
@@ -5012,9 +5018,7 @@ static void show_one_worker_pool(struct worker_pool *pool) · 2 unmodified lines
5012	5018	printk_deferred_enter();
5013	5019	pr_info("pool %d:", pool->id);
5014	5020	pr_cont_pool_info(pool);
5015		− pr_cont(" hung=%us workers=%d",
5016		− jiffies_to_msecs(jiffies - pool->watchdog_ts) / 1000,
5017		− pool->nr_workers);
	5021	+ pr_cont(" hung=%lus workers=%d", hung, pool->nr_workers);
5018	5022	if (pool->manager)
5019	5023	pr_cont(" manager: %d",
5020	5024	task_pid_nr(pool->manager->task));