workqueue: Provide a handshake for canceling BH workers

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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@linutronix.de>
Signed-off-by: Tejun Heo <tj@kernel.org>

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Sebastian Andrzej Siewior 2025-09-04 16:25:23 +02:00 • committed by Tejun Heo

parent cda2b2d647

commit ad7c7f4b9c

1 changed files with 41 additions and 9 deletions

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kernel/workqueue.c

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