linux-kernel - Re: [PATCH v2] signal: break out of wait loops on kthread

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Date:   Tue, 28 Jun 2022 17:59:11 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     linux-kernel@...r.kernel.org, mingo@...hat.com,
        peterz@...radead.org,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        Kalle Valo <kvalo@...nel.org>,
        Johannes Berg <johannes@...solutions.net>
Subject: Re: [PATCH v2] signal: break out of wait loops on kthread_stop()

Hi Eric,

On Mon, Jun 27, 2022 at 02:16:08PM -0500, Eric W. Biederman wrote:
> Semantically this makes a lot of sense.
> 
> Bloating up signal_pending which is mainly called in non-kthread
> contexts is undesirable.

I guess I understand that concern, but does it really matter here? This
is called by code that waits anyway, so it's not like performance
matters at all, right?

> Instead could you modify kthread_stop to call set_notify_signal().
> 
> That is exactly what set_notify_signal is there for.  When you don't
> actually have a signal but you want to break out of an interruptible
> loop.  My last round of work in the area decoupled set_notify_signal
> from any other semantics.

This sounds like the best option here, if in fact it does work. I'll
send in a patch for that and we can see how it interacts with the other
work you're doing.

Jason