linux-kernel - [RFC PATCH] workqueue: introduce WORK_STRUCT_TIMER_PENDING

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Message-Id: <20241230064500.1404206-1-imran.f.khan@oracle.com>
Date: Mon, 30 Dec 2024 17:45:00 +1100
From: Imran Khan <imran.f.khan@...cle.com>
To: tj@...nel.org, jiangshanlai@...il.com
Cc: linux-kernel@...r.kernel.org
Subject: [RFC PATCH] workqueue: introduce WORK_STRUCT_TIMER_PENDING_BIT.

Currently WORK_STRUCT_PENDING_BIT can indicate a work_struct that is
already made it to work list of a worker_pool or a work_struct that has
not yet made it there because it comes from a delayed_work whose timer
has not expired yet.

Use WORK_STRUCT_TIMER_PENDING_BIT to distinguish between these two
states of work_struct.

Signed-off-by: Imran Khan <imran.f.khan@...cle.com>
---
I have kept the patch as RFC, because this change is not fixing a bug.
It makes WORK_STRUCT_PENDING_BIT less ambiguous and helps in debugging,
by indicating where one should look for this pending work.

 include/linux/workqueue.h | 1 +
 kernel/workqueue.c        | 2 ++
 2 files changed, 3 insertions(+)

diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index b0dc957c3e560..2d327d9e9b53a 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -27,6 +27,7 @@ enum work_bits {
 	WORK_STRUCT_INACTIVE_BIT,	/* work item is inactive */
 	WORK_STRUCT_PWQ_BIT,		/* data points to pwq */
 	WORK_STRUCT_LINKED_BIT,		/* next work is linked to this one */
+	WORK_STRUCT_TIMER_PENDING_BIT,	/* timer pending for delayed work */
 #ifdef CONFIG_DEBUG_OBJECTS_WORK
 	WORK_STRUCT_STATIC_BIT,		/* static initializer (debugobjects) */
 #endif
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index eb71e3d9d16dd..454382a9a1585 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -2481,6 +2481,7 @@ void delayed_work_timer_fn(struct timer_list *t)
 {
 	struct delayed_work *dwork = from_timer(dwork, t, timer);
 
+	clear_bit(WORK_STRUCT_TIMER_PENDING_BIT, work_data_bits(&dwork->work));
 	/* should have been called from irqsafe timer with irq already off */
 	__queue_work(dwork->cpu, dwork->wq, &dwork->work);
 }
@@ -2511,6 +2512,7 @@ static void __queue_delayed_work(int cpu, struct workqueue_struct *wq,
 	dwork->wq = wq;
 	dwork->cpu = cpu;
 	timer->expires = jiffies + delay;
+	set_bit(WORK_STRUCT_TIMER_PENDING_BIT, work_data_bits(work));
 
 	if (housekeeping_enabled(HK_TYPE_TIMER)) {
 		/* If the current cpu is a housekeeping cpu, use it. */

base-commit: 8155b4ef3466f0e289e8fcc9e6e62f3f4dceeac2
-- 
2.34.1