linux-kernel - Re: [PATCH] workqueue: flush all pending jobs in destroy

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Message-ID: <aAqXw3t9UVU8pF8_@slm.duckdns.org>
Date: Thu, 24 Apr 2025 09:57:55 -1000
From: Tejun Heo <tj@...nel.org>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: Lai Jiangshan <jiangshanlai@...il.com>,
	Philipp Stanner <phasta@...lbox.org>,
	Danilo Krummrich <dakr@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] workqueue: flush all pending jobs in destroy_workqueue()

Hello, Alice.

On Wed, Apr 23, 2025 at 05:51:27PM +0000, Alice Ryhl wrote:
...
> @@ -367,6 +367,8 @@ struct workqueue_struct {
>  	struct lockdep_map	__lockdep_map;
>  	struct lockdep_map	*lockdep_map;
>  #endif
> +	raw_spinlock_t		delayed_lock;	/* protects pending_list */
> +	struct list_head	delayed_list;	/* list of pending delayed jobs */

I think we'll have to make this per-CPU or per-pwq. There can be a lot of
delayed work items being queued on, e.g., system_wq. Imagine that happening
on a multi-socket NUMA system. That cacheline is going to be bounced around
pretty hard.

Thanks.

-- 
tejun