linux-kernel - Re: [PATCH v7 4/4] workqueue: Unbind kworkers before sending them to exit()

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Message-ID: <Y77qEu1fQHMWr6F1@slm.duckdns.org>
Date:   Wed, 11 Jan 2023 06:55:46 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Valentin Schneider <vschneid@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Phil Auld <pauld@...hat.com>,
        Marcelo Tosatti <mtosatti@...hat.com>
Subject: Re: [PATCH v7 4/4] workqueue: Unbind kworkers before sending them to
 exit()

On Wed, Jan 11, 2023 at 12:49:49PM +0000, Valentin Schneider wrote:
> While we're here, for my own education I was trying to figure out in what
> scenarios we can hit this manager-already-active condition. When sending
> out v6 I had convinced myself it could happen during failed
> initialization of a new unbound pool, but having another look at it now I'm
> not so sure anymore.
> 
> The only scenario I can think of now is around maybe_create_worker()'s
> release of pool->lock, as that implies another worker can drain the
> pool->worklist and thus let pool->refcnt reach 0 while another worker is
> being the pool manager. Am I looking at the right thing?

To be frank, I'm not sure and can't remember why the code is like that off
the top of my head. It could well be that I was just habitually thinking
that MANAGER can be contended while in practice the scenario can never
happen in this particular case. I'll need to look harder at it but maybe we
can leave that to another day?

Thanks.

-- 
tejun