linux-kernel - Re: [PATCH v2] workqueue: Add rcu lock check after work execute end

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Date: Tue, 16 Jan 2024 10:22:18 -1000
From: Tejun Heo <tj@...nel.org>
To: Xuewen Yan <xuewen.yan@...soc.com>
Cc: longman@...hat.com, jiangshanlai@...il.com, ke.wang@...soc.com,
	xuewen.yan94@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] workqueue: Add rcu lock check after work execute end

Hello,

I massaged the description for clarity and applied to wq/for-6.9.

Thanks.

>From 1a65a6d17cbc58e1aeffb2be962acce49efbef9c Mon Sep 17 00:00:00 2001
From: Xuewen Yan <xuewen.yan@...soc.com>
Date: Wed, 10 Jan 2024 11:27:24 +0800
Subject: [PATCH] workqueue: Add rcu lock check at the end of work item
 execution

Currently the workqueue just checks the atomic and locking states after work
execution ends. However, sometimes, a work item may not unlock rcu after
acquiring rcu_read_lock(). And as a result, it would cause rcu stall, but
the rcu stall warning can not dump the work func, because the work has
finished.

In order to quickly discover those works that do not call rcu_read_unlock()
after rcu_read_lock(), add the rcu lock check.

Use rcu_preempt_depth() to check the work's rcu status. Normally, this value
is 0. If this value is bigger than 0, it means the work are still holding
rcu lock. If so, print err info and the work func.

tj: Reworded the description for clarity. Minor formatting tweak.

Signed-off-by: Xuewen Yan <xuewen.yan@...soc.com>
Reviewed-by: Lai Jiangshan <jiangshanlai@...il.com>
Reviewed-by: Waiman Long <longman@...hat.com>
Signed-off-by: Tejun Heo <tj@...nel.org>
---
 kernel/workqueue.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index ed442cefea7c..aec3efbaaf93 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -2640,11 +2640,12 @@ __acquires(&pool->lock)
 	lock_map_release(&lockdep_map);
 	lock_map_release(&pwq->wq->lockdep_map);

-	if (unlikely(in_atomic() || lockdep_depth(current) > 0)) {
-		pr_err("BUG: workqueue leaked lock or atomic: %s/0x%08x/%d\n"
+	if (unlikely(in_atomic() || lockdep_depth(current) > 0 ||
+		     rcu_preempt_depth() > 0)) {
+		pr_err("BUG: workqueue leaked lock or atomic: %s/0x%08x/%d/%d\n"
 		       "     last function: %ps\n",
-		       current->comm, preempt_count(), task_pid_nr(current),
-		       worker->current_func);
+		       current->comm, preempt_count(), rcu_preempt_depth(),
+		       task_pid_nr(current), worker->current_func);
 		debug_show_held_locks(current);
 		dump_stack();
 	}
-- 
2.43.0