linux-kernel - Re: [4.19 stable-rt PATCH] tasklet: Fix UP case for tasklet CHAINED state

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Message-ID: <5ed2c074f367c2939d0cce494b85f9f5d74d4234.camel@kernel.org>
Date:   Tue, 09 Jun 2020 11:59:11 -0500
From:   Tom Zanussi <zanussi@...nel.org>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     linux-rt-users <linux-rt-users@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [4.19 stable-rt PATCH] tasklet: Fix UP case for tasklet CHAINED
 state

Hi Sebastian,

On Tue, 2020-06-09 at 18:38 +0200, Sebastian Andrzej Siewior wrote:
> On 2020-06-09 11:21:44 [-0500], Tom Zanussi wrote:
> > index 73dae64bfc9c..4f37a6173ab9 100644
> > --- a/kernel/softirq.c
> > +++ b/kernel/softirq.c
> > @@ -947,10 +947,12 @@ static void __tasklet_schedule_common(struct
> > tasklet_struct *t,
> >  	 * is locked before adding it to the list.
> >  	 */
> >  	if (test_bit(TASKLET_STATE_SCHED, &t->state)) {
> > +#if defined(CONFIG_SMP)
> >  		if (test_and_set_bit(TASKLET_STATE_CHAINED, &t->state)) 
> > {
> >  			tasklet_unlock(t);
> >  			return;
> >  		}
> > +#endif
> >  		t->next = NULL;
> >  		*head->tail = t;
> >  		head->tail = &(t->next);
> > @@ -1044,7 +1046,11 @@ static void tasklet_action_common(struct
> > softirq_action *a,
> >  again:
> >  		t->func(t->data);
> >  
> > +#if !defined(CONFIG_SMP)
> > +		while (!tasklet_tryunlock(t)) {
> > +#else
> >  		while (cmpxchg(&t->state, TASKLET_STATEF_RC, 0) !=
> > TASKLET_STATEF_RC) {
> > +#endif
> 
> This is still needed for RT && !SMP
> 

Yes, you're right - I'll change this and repost after testing all
cases.

Thanks,

Tom

> >  			/*
> >  			 * If it got disabled meanwhile, bail out:
> >  			 */
> 
> Sebastian