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

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Message-ID: <xhsmhpmblc7my.mognet@vschneid.remote.csb>
Date:   Wed, 11 Jan 2023 17:18:13 +0000
From:   Valentin Schneider <vschneid@...hat.com>
To:     Tejun Heo <tj@...nel.org>
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 11/01/23 06:55, Tejun Heo wrote:
> 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?
>

For sure :-)

> Thanks.
>
> -- 
> tejun