linux-kernel - Re: [PATCH v3 1/2] livepatch: send a fake signal to all blocking tasks

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Date:   Thu, 2 Nov 2017 15:08:53 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     Miroslav Benes <mbenes@...e.cz>
Cc:     Petr Mladek <pmladek@...e.com>, jpoimboe@...hat.com,
        jeyu@...nel.org, jikos@...nel.org, lpechacek@...e.cz, pavel@....cz,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
        Michael Ellerman <mpe@...erman.id.au>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        linuxppc-dev@...ts.ozlabs.org, x86@...nel.org
Subject: Re: [PATCH v3 1/2] livepatch: send a fake signal to all blocking
 tasks

On 11/02, Miroslav Benes wrote:
>
> On Wed, 1 Nov 2017, Oleg Nesterov wrote:
>
> > Note also that wake_up_state(TASK_INTERRUPTIBLE) won't wakeup the TASK_IDLE
> > kthreads, and most of the kthreads which use TASK_INTERRUPTIBLE should use
> > TASK_IDLE today, because in most cases TASK_INTERRUPTIBLE was used to not
> > contribute to loadavg.
>
> Yes. Unfortunately, we have TASK_IDLE for more than two years now and
> nothing much has happened yet. TASK_IDLE is still used sporadically. I'd
> like to be on the safe side with livepatch

OK, as I said I won't argue,

> and given that
> TASK_INTERRUPTIBLE loops should be prepared for spurious wakeups by
> definition,

Not really when it comes to kthreads.

Once again, unless kthread does allow_signal() TASK_INTERRUPTIBLE does
not really differ from TASK_UNINTERRUPTIBLE except the latter contributes
to loadavg. And that is why TASK_INTERRUPTIBLE was commonly used instead
of TASK_UNINTERRUPTIBLE, so I do not think that TASK_INTERRUPTIBLE loops
are more ready in general than TASK_UNINTERRUPTIBLE.

Oleg.