Patch "workqueue: Fix hung time report of worker pools" has been added to the 5.15-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

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

    workqueue: Fix hung time report of worker pools

to the 5.15-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-fix-hung-time-report-of-worker-pools.patch
and it can be found in the queue-5.15 subdirectory.

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



commit e9a11e7ee14b232be482322fac960ea989f4b3cd
Author: Petr Mladek <pmladek@xxxxxxxx>
Date:   Tue Mar 7 13:53:31 2023 +0100

    workqueue: Fix hung time report of worker pools
    
    [ Upstream commit 335a42ebb0ca8ee9997a1731aaaae6dcd704c113 ]
    
    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.
    
    Fixes: 82607adcf9cdf40fb7b ("workqueue: implement lockup detector")
    Signed-off-by: Petr Mladek <pmladek@xxxxxxxx>
    Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index de6463b931762..2d27bed9881dd 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -4857,10 +4857,16 @@ static void show_one_worker_pool(struct worker_pool *pool)
 	struct worker *worker;
 	bool first = true;
 	unsigned long flags;
+	unsigned long hung = 0;
 
 	raw_spin_lock_irqsave(&pool->lock, flags);
 	if (pool->nr_workers == pool->nr_idle)
 		goto next_pool;
+
+	/* How long the first pending work is waiting for a worker. */
+	if (!list_empty(&pool->worklist))
+		hung = jiffies_to_msecs(jiffies - pool->watchdog_ts) / 1000;
+
 	/*
 	 * Defer printing to avoid deadlocks in console drivers that
 	 * queue work while holding locks also taken in their write
@@ -4869,9 +4875,7 @@ static void show_one_worker_pool(struct worker_pool *pool)
 	printk_deferred_enter();
 	pr_info("pool %d:", pool->id);
 	pr_cont_pool_info(pool);
-	pr_cont(" hung=%us workers=%d",
-		jiffies_to_msecs(jiffies - pool->watchdog_ts) / 1000,
-		pool->nr_workers);
+	pr_cont(" hung=%lus workers=%d", hung, pool->nr_workers);
 	if (pool->manager)
 		pr_cont(" manager: %d",
 			task_pid_nr(pool->manager->task));