linux-kernel - Re: [Intel-gfx] signal: break out of wait loops on kthread

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Message-ID: <Y1Bby6FEEWiFIjjD@zx2c4.com>
Date:   Wed, 19 Oct 2022 14:19:23 -0600
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>
Cc:     "Intel-gfx@...ts.freedesktop.org" <Intel-gfx@...ts.freedesktop.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        linux-kernel@...r.kernel.org, sultan@...neltoast.com
Subject: Re: [Intel-gfx] signal: break out of wait loops on kthread_stop()

On Wed, Oct 19, 2022 at 09:09:28PM +0100, Tvrtko Ursulin wrote:
> Hm why is kthread_stop() after kthread_run() abuse? I don't see it in 
> kerneldoc that it must not be used for stopping threads.

Because you don't want it to stop. You want to wait until it's done. If
you call stop right after run, it will even stop it before it even
begins to run. That's why you wind up sprinkling your msleeps
everywhere, indicating that clearly this is not meant to work that way.

> Yep the yields and sleeps are horrible and will go. But they are also 
> not relevant for the topic at hand.

Except they very much are. The reason you need these is because you're
using kthread_stop() for something it's not meant to do.

> Never mind, I was not looking for anything more than a suggestion on how 
> to maybe work around it in piece as someone is dealing with the affected 
> call sites.

Sultan's kthread_work idea is probably the right direction. This would
seem to have what you need.

Jason