linux-kernel - Re: [PATCH workqueue/for-4.14-fixes] workqueue: replace pool->manager

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Message-ID: <20171009150808.GD3301751@devbig577.frc2.facebook.com>
Date:   Mon, 9 Oct 2017 08:08:08 -0700
From:   Tejun Heo <tj@...nel.org>
To:     Lai Jiangshan <jiangshanlai@...il.com>
Cc:     Boqun Feng <boqun.feng@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Josef Bacik <josef@...icpanda.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH workqueue/for-4.14-fixes] workqueue: replace
 pool->manager_arb mutex with a flag

Hello,

On Mon, Oct 09, 2017 at 11:02:34PM +0800, Lai Jiangshan wrote:
> I was also thinking alternative code when reviewing.
> The first is quite obvious. Testing POOL_MANAGER_ACTIVE
> can be replaced by testing pool->manager.
> And POOL_MANAGER_ACTIVE  is not needed. Isn't it?

put_unbound_pool() doesn't have to be called from a kworker context
and we don't really have a kworker pointer to set pool->manager to.
We can use a bogus value and then update pool->manager dereferences
accordingly but I think it's cleaner to simply use a separate flag.

> The second thing is to make manage_workers()
> and put_unbound_pool() exclusive.
> Waiting event on POOL_MANAGER_ACTIVE(or pool->manager)
> is one way. However, the pool's refcnt is not possible to
> be dropped to zero now since the caller still hold the pool->lock

wait_event_lock_irq() drops the lock if the condition is not met
before going to sleep (otherwise it wouldn't be able to sleep).

> and some pwds of the works in the worklist. So the other way
> to enforce the exclusive could be just doing
> get_pwq(the first pwd of the worklist) and put_pwq() when
> the manage_workers() done. And the code about
> pool->manager_arb in put_unbound_pool() can be
> simply removed.

Yeah, that part is removed.

Thanks!

-- 
tejun