linux-kernel - Re: [PATCH v3 1/3] workqueue: Provide a handshake for canceling BH workers

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Message-ID: <aLnMVqcHFQPnKHyi@slm.duckdns.org>
Date: Thu, 4 Sep 2025 07:28:54 -1000
From: Tejun Heo <tj@...nel.org>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: linux-rt-devel@...ts.linux.dev, linux-kernel@...r.kernel.org,
	Clark Williams <clrkwllms@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v3 1/3] workqueue: Provide a handshake for canceling BH
 workers

On Thu, Sep 04, 2025 at 04:25:23PM +0200, Sebastian Andrzej Siewior wrote:
> While a BH work item is canceled, the core code spins until it
> determines that the item completed. On PREEMPT_RT the spinning relies on
> a lock in local_bh_disable() to avoid a live lock if the canceling
> thread has higher priority than the BH-worker and preempts it. This lock
> ensures that the BH-worker makes progress by PI-boosting it.
> 
> This lock in local_bh_disable() is a central per-CPU BKL and about to be
> removed.
> 
> To provide the required synchronisation add a per pool lock. The lock is
> acquired by the bh_worker at the begin while the individual callbacks
> are invoked. To enforce progress in case of interruption, __flush_work()
> needs to acquire the lock.
> This will flush all BH-work items assigned to that pool.
> 
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>

Applied to wq/for-6.18.

Thanks.

-- 
tejun