linux-kernel - Re: [RESEND][PATCH v21 2/6] sched/locking: Add blocked_on_state to provide necessary tri-state for proxy return-migration

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Message-ID: <CANDhNCrPeJpNYtHEZY46etXb_c4H4dALELf2LbC1R8PnWJW97w@mail.gmail.com>
Date: Tue, 23 Sep 2025 16:34:13 -0700
From: John Stultz <jstultz@...gle.com>
To: K Prateek Nayak <kprateek.nayak@....com>
Cc: LKML <linux-kernel@...r.kernel.org>, Joel Fernandes <joelagnelf@...dia.com>, 
	Qais Yousef <qyousef@...alina.io>, Ingo Molnar <mingo@...hat.com>, 
	Peter Zijlstra <peterz@...radead.org>, Juri Lelli <juri.lelli@...hat.com>, 
	Vincent Guittot <vincent.guittot@...aro.org>, Dietmar Eggemann <dietmar.eggemann@....com>, 
	Valentin Schneider <vschneid@...hat.com>, Steven Rostedt <rostedt@...dmis.org>, 
	Ben Segall <bsegall@...gle.com>, Zimuzo Ezeozue <zezeozue@...gle.com>, Mel Gorman <mgorman@...e.de>, 
	Will Deacon <will@...nel.org>, Waiman Long <longman@...hat.com>, Boqun Feng <boqun.feng@...il.com>, 
	"Paul E. McKenney" <paulmck@...nel.org>, Metin Kaya <Metin.Kaya@....com>, 
	Xuewen Yan <xuewen.yan94@...il.com>, Thomas Gleixner <tglx@...utronix.de>, 
	Daniel Lezcano <daniel.lezcano@...aro.org>, Suleiman Souhlal <suleiman@...gle.com>, 
	kuyo chang <kuyo.chang@...iatek.com>, hupu <hupu.gm@...il.com>, kernel-team@...roid.com
Subject: Re: [RESEND][PATCH v21 2/6] sched/locking: Add blocked_on_state to
 provide necessary tri-state for proxy return-migration

On Thu, Sep 18, 2025 at 8:28 PM K Prateek Nayak <kprateek.nayak@....com> wrote:
> On 9/19/2025 4:27 AM, John Stultz wrote:
> >> I didn't know that was possible! Neat. Since cleanup.h has a note
> >> reading:
> >>
> >>     ... the expectation is that usage of "goto" and cleanup helpers is
> >>     never mixed in the same function.
> >>
> >> are there any concerns w.r.t. compiler versions etc. or am I just being
> >> paranoid?
> >
> > Hrrrrmmmm.  I hadn't seen that detail. :/   I guess I was just lucky
> > it worked with my toolchain.
>
> I have been too. Maybe it is okay to use a goto if folks know what
> they are doing ¯\_(ツ)_/¯
>
> Another idea is to have:
>
>     bool deactivate_donor = false;
>
>     for (p = donor; task_is_blocked(p); p = owner) {
>         guard(raw_spinlock)(...);
>         ...
>         if (<condition> {
>             deactivate_donor = true;
>             break;
>         }
>         ...
>     }
>     if (deactivate_donor)
>         return proxy_deactivate(rq, donor);
>
> Can that work?

Yeah, I've reworked the logic to switch() on an action enum, which
will let us do something similar without gotos.

thanks
-john