linux-kernel - Re: [PATCH] workqueue: replace call_rcu with kfree

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Message-ID: <20201026134010.GA73258@mtj.duckdns.org>
Date:   Mon, 26 Oct 2020 09:41:14 -0400
From:   Tejun Heo <tj@...nel.org>
To:     qiang.zhang@...driver.com
Cc:     jiangshanlai@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] workqueue: replace call_rcu with kfree_rcu

On Wed, Oct 14, 2020 at 04:31:45PM +0800, qiang.zhang@...driver.com wrote:
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index ac088ce6059b..8d4fe649631a 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -3653,11 +3653,6 @@ static struct worker_pool *get_unbound_pool(const struct workqueue_attrs *attrs)
>  	return NULL;
>  }
>  
> -static void rcu_free_pwq(struct rcu_head *rcu)
> -{
> -	kmem_cache_free(pwq_cache,
> -			container_of(rcu, struct pool_workqueue, rcu));
> -}
>  
>  /*
>   * Scheduled on system_wq by put_pwq() when an unbound pwq hits zero refcnt
> @@ -3683,7 +3678,7 @@ static void pwq_unbound_release_workfn(struct work_struct *work)
>  	put_unbound_pool(pool);
>  	mutex_unlock(&wq_pool_mutex);
>  
> -	call_rcu(&pwq->rcu, rcu_free_pwq);
> +	kfree_rcu(pwq, rcu);

kfree_rcu() eventually calls kfree() which is different from
kmem_cache_free(). It can only be used for kmalloc'd areas, not
kmem_cache_alloc'd ones.

Thanks.

-- 
tejun