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

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Date: Wed, 10 Jan 2024 09:28:16 -0500
From: Waiman Long <longman@...hat.com>
To: Xuewen Yan <xuewen.yan@...soc.com>, tj@...nel.org
Cc: 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

On 1/9/24 22:27, Xuewen Yan wrote:
> 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();
>   	}

This can be a useful additional sanity test.

Reviewed-by: Waiman Long <longman@...hat.com>