linux-kernel - Re: [PATCH v3] softirq: Prevent looping on disabled tasklets

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Date:   Fri, 17 Feb 2017 12:55:56 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Chris Wilson <chris@...is-wilson.co.uk>
cc:     linux-kernel@...r.kernel.org, intel-gfx@...ts.freedesktop.org,
        Tvrtko Ursulin <tvrtko.ursulin@...el.com>,
        Hannes Reinecke <hare@...e.com>, Jens Axboe <axboe@...nel.dk>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        Chen Fan <chen.fan.fnst@...fujitsu.com>,
        Ingo Molnar <mingo@...nel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Johannes Thumshirn <jthumshirn@...e.de>,
        Emese Revfy <re.emese@...il.com>,
        Sagi Grimberg <sagi@...mberg.me>,
        Eric Dumazet <edumazet@...gle.com>,
        Tom Herbert <therbert@...gle.com>,
        Ben Hutchings <bhutchings@...arflare.com>
Subject: Re: [PATCH v3] softirq: Prevent looping on disabled tasklets

On Sun, 12 Feb 2017, Chris Wilson wrote:

> On Sun, Feb 12, 2017 at 03:46:09PM +0000, Chris Wilson wrote:
> > +void tasklet_enable(struct tasklet_struct *t)
> > +{
> > +	if (!atomic_dec_and_test(&t->count))
> > +		return;
> > +
> > +	if (test_bit(TASKLET_STATE_SCHED, &t->state))
> > +		raise_softirq(HI_SOFTIRQ | TASKLET_SOFTIRQ);
> 
> And of course this can't work as raise_softirq() is local to the cpu.

Indeed. tasklets are a horror by design. We rather should make them go away.

Thanks,

	tglx