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

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Date: Wed, 10 Jan 2024 11:27:24 +0800
From: Xuewen Yan <xuewen.yan@...soc.com>
To: <tj@...nel.org>, <longman@...hat.com>
CC: <jiangshanlai@...il.com>, <ke.wang@...soc.com>, <xuewen.yan94@...il.com>,
        <linux-kernel@...r.kernel.org>
Subject: [PATCH v2] workqueue: Add rcu lock check after work execute end

Now the workqueue just check the atomic and lock after
work execute end. However, sometimes, drivers's work
may don't unlock rcu after call 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.
At this time, we print err info and print the work func.

Signed-off-by: Xuewen Yan <xuewen.yan@...soc.com>
---
V2:
- move check to unlikely() helper (Longman)
---
 kernel/workqueue.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 2989b57e154a..c2a73364f5ad 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -2634,11 +2634,12 @@ __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();
 	}
-- 
2.25.1