linux-kernel - Re: [PATCH] softirq: Reserve a bit in tasklet.state for the user

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Date:   Mon, 23 Jan 2017 16:59:32 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Jens Axboe <axboe@...nel.dk>
cc:     Chris Wilson <chris@...is-wilson.co.uk>,
        LKML <linux-kernel@...r.kernel.org>,
        Hannes Reinecke <hare@...e.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Chen Fan <chen.fan.fnst@...fujitsu.com>,
        Alexander Potapenko <glider@...gle.com>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] softirq: Reserve a bit in tasklet.state for the user

On Mon, 23 Jan 2017, Jens Axboe wrote:

> On 01/23/2017 08:33 AM, Chris Wilson wrote:
> > Allow the user to communicate with the tasklet through the atomic state
> > field by assigning a bit for their use. This can be used, for example,
> > to differentiate between a tasklet called following an irq or from
> > process context, where some hardware state may only be valid after the
> > irq.
> > 
> > Signed-off-by: Chris Wilson <chris@...is-wilson.co.uk>
> > Cc: Thomas Gleixner <tglx@...utronix.de>
> > Cc: Jens Axboe <axboe@...nel.dk>
> > Cc: Hannes Reinecke <hare@...e.com>
> > Cc: Bjorn Helgaas <bhelgaas@...gle.com>
> > Cc: Chen Fan <chen.fan.fnst@...fujitsu.com>
> > Cc: Alexander Potapenko <glider@...gle.com>
> > ---
> >  include/linux/interrupt.h | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
> > index 53144e78a369..ab321552089b 100644
> > --- a/include/linux/interrupt.h
> > +++ b/include/linux/interrupt.h
> > @@ -542,7 +542,8 @@ struct tasklet_struct name = { NULL, 0, ATOMIC_INIT(1), func, data }
> >  enum
> >  {
> >  	TASKLET_STATE_SCHED,	/* Tasklet is scheduled for execution */
> > -	TASKLET_STATE_RUN	/* Tasklet is running (SMP only) */
> > +	TASKLET_STATE_RUN,	/* Tasklet is running (SMP only) */
> > +	TASKLET_STATE_USER	/* Reserved for use by the owner */
> >  };
> 
> I have no problem making that distinction, but it's impossible to ack
> this patch without having seen how you plan to utilize it, as the patch
> is meaningless on its own.

Right and w/o well defined semantics of this bit it's not at all
acceptable. tasklets have vagely semantics already, we really don't need to
increase that horror.

Thanks,

	tglx