linux-kernel - [PATCH 3/4] workqueue: Show in-flight work item duration in stall diagnostics

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Message-Id: <20260211-wqstall_start-at-v1-3-bd9499a18c19@debian.org>
Date: Wed, 11 Feb 2026 04:29:17 -0800
From: Breno Leitao <leitao@...ian.org>
To: Tejun Heo <tj@...nel.org>, Lai Jiangshan <jiangshanlai@...il.com>, 
 Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org, Omar Sandoval <osandov@...ndov.com>, 
 kernel-team@...a.com, Breno Leitao <leitao@...ian.org>
Subject: [PATCH 3/4] workqueue: Show in-flight work item duration in stall
 diagnostics

When diagnosing workqueue stalls, knowing how long each in-flight work
item has been executing is valuable. Add a current_start timestamp
(jiffies) to struct worker, set it when a work item begins execution in
process_one_work(), and print the elapsed wall-clock time in show_pwq().

Unlike current_at (which tracks CPU runtime and resets on wakeup for
CPU-intensive detection), current_start is never reset because the
diagnostic cares about total wall-clock time including sleeps.

Before: in-flight: 165:stall_work_fn [wq_stall]
After:  in-flight: 165:stall_work_fn [wq_stall] for 100s

Signed-off-by: Breno Leitao <leitao@...ian.org>
---
 kernel/workqueue.c          | 3 +++
 kernel/workqueue_internal.h | 1 +
 2 files changed, 4 insertions(+)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index b3ba739cf493a..e527e763162e6 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -3204,6 +3204,7 @@ __acquires(&pool->lock)
 	worker->current_pwq = pwq;
 	if (worker->task)
 		worker->current_at = worker->task->se.sum_exec_runtime;
+	worker->current_start = jiffies;
 	work_data = *work_data_bits(work);
 	worker->current_color = get_work_color(work_data);
 
@@ -6359,6 +6360,8 @@ static void show_pwq(struct pool_workqueue *pwq)
 			pr_cont(" %s", comma ? "," : "");
 			pr_cont_worker_id(worker);
 			pr_cont(":%ps", worker->current_func);
+			pr_cont(" for %us",
+				jiffies_to_msecs(jiffies - worker->current_start) / 1000);
 			list_for_each_entry(work, &worker->scheduled, entry)
 				pr_cont_work(false, work, &pcws);
 			pr_cont_work_flush(comma, (work_func_t)-1L, &pcws);
diff --git a/kernel/workqueue_internal.h b/kernel/workqueue_internal.h
index f6275944ada77..8def1ddc5a1bf 100644
--- a/kernel/workqueue_internal.h
+++ b/kernel/workqueue_internal.h
@@ -32,6 +32,7 @@ struct worker {
 	work_func_t		current_func;	/* K: function */
 	struct pool_workqueue	*current_pwq;	/* K: pwq */
 	u64			current_at;	/* K: runtime at start or last wakeup */
+	unsigned long		current_start;	/* K: start time of current work item */
 	unsigned int		current_color;	/* K: color */
 
 	int			sleeping;	/* S: is worker sleeping? */

-- 
2.47.3