From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Lai Jiangshan <laijs@linux.alibaba.com>
Cc: linux-kernel@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@kernel.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Tejun Heo <tj@kernel.org>, Lai Jiangshan <jiangshanlai@gmail.com>
Subject: Re: [PATCH 1/2] workqueue: pin the pool while it is managing
Date: Thu, 28 May 2020 10:08:44 +0200 [thread overview]
Message-ID: <20200528080844.37wgxcy77uu7pmmz@linutronix.de> (raw)
In-Reply-To: <20200528030657.1690-1-laijs@linux.alibaba.com>
On 2020-05-28 03:06:55 [+0000], Lai Jiangshan wrote:
> So that put_unbound_pool() can ensure all workers in idle,
> no unfinished manager. And it doens't need to wait any manager
> and can go to delete all the idle workers straight away.
>
> Also removes manager waitqueue, because it is unneeded and as
> Sebastian Andrzej Siewior said:
>
> The workqueue code has it's internal spinlock (pool::lock) and also
> implicit spinlock usage in the wq_manager waitqueue. These spinlocks
> are converted to 'sleeping' spinlocks on a RT-kernel.
>
> Workqueue functions can be invoked from contexts which are truly atomic
> even on a PREEMPT_RT enabled kernel. Taking sleeping locks from such
> contexts is forbidden.
>
> pool::lock can be converted to a raw spinlock as the lock held times
> are short. But the workqueue manager waitqueue is handled inside of
> pool::lock held regions which again violates the lock nesting rules
> of raw and regular spinlocks.
This seems to work for my test case I had test my chance. And lockdep
didn't complain so…
If you prefer this over my 1/2 what do we do about 2/2? Do you want me
to repost it?
Sebastian
next prev parent reply other threads:[~2020-05-28 8:08 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-27 19:46 [PATCH v2 0/2] workqueue: Make the workqueue code PREEMPT_RT safe Sebastian Andrzej Siewior
2020-05-27 19:46 ` [PATCH v2 1/2] workqueue: Use rcuwait for wq_manager_wait Sebastian Andrzej Siewior
2020-05-28 3:06 ` [PATCH 1/2] workqueue: pin the pool while it is managing Lai Jiangshan
2020-05-28 3:06 ` [PATCH 2/2] workqueue: remove useless POOL_MANAGER_ACTIVE Lai Jiangshan
2020-05-28 8:08 ` Sebastian Andrzej Siewior [this message]
2020-05-28 8:35 ` [PATCH 1/2] workqueue: pin the pool while it is managing Lai Jiangshan
2020-05-28 14:35 ` Tejun Heo
2020-05-29 5:33 ` Lai Jiangshan
2020-05-27 19:46 ` [PATCH v2 2/2] workqueue: Convert the pool::lock and wq_mayday_lock to raw_spinlock_t Sebastian Andrzej Siewior
2020-05-28 0:33 ` Lai Jiangshan
2020-05-29 14:04 ` Tejun Heo
2020-05-27 22:57 ` [PATCH v2 0/2] workqueue: Make the workqueue code PREEMPT_RT safe Linus Torvalds
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