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

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Date:   Tue, 9 Jun 2020 18:38:32 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Tom Zanussi <zanussi@...nel.org>
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

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

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

Sebastian