From: Peter Zijlstra <peterz@infradead.org>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Corey Minyard <cminyard@mvista.com>,
Thomas Gleixner <tglx@linutronix.de>,
Steven Rostedt <rostedt@goodmis.org>,
linux-rt-users <linux-rt-users@vger.kernel.org>,
linux-kernel <linux-kernel@vger.kernel.org>,
Tejun Heo <tj@kernel.org>
Subject: Re: Warning from swake_up_all in 4.14.15-rt13 non-RT
Date: Fri, 9 Mar 2018 18:46:05 +0100 [thread overview]
Message-ID: <20180309174605.GC4064@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20180309110418.lwtennjqwqcxh422@linutronix.de>
On Fri, Mar 09, 2018 at 12:04:18PM +0100, Sebastian Andrzej Siewior wrote:
> +void swake_add_all_wq(struct swait_queue_head *q, struct wake_q_head *wq)
> {
> struct swait_queue *curr;
>
> while (!list_empty(&q->task_list)) {
>
> curr = list_first_entry(&q->task_list, typeof(*curr),
> task_list);
> list_del_init(&curr->task_list);
> + wake_q_add(wq, curr->task);
> }
> }
> +EXPORT_SYMBOL(swake_add_all_wq);
>
> void swake_up(struct swait_queue_head *q)
> {
> @@ -66,25 +62,14 @@ EXPORT_SYMBOL(swake_up);
> */
> void swake_up_all(struct swait_queue_head *q)
> {
> + unsigned long flags;
> + DEFINE_WAKE_Q(wq);
>
> + raw_spin_lock_irqsave(&q->lock, flags);
> + swake_add_all_wq(q, &wq);
> + raw_spin_unlock_irqrestore(&q->lock, flags);
>
> + wake_up_q(&wq);
> }
> EXPORT_SYMBOL(swake_up_all);
This is fundamentally wrong. The whole point of wake_up_all() is that
_all_ is unbounded and should not ever land in a single critical
section, be it IRQ or PREEMPT disabled. The above does both.
Yes, wake_up_all() is crap, it is also fundamentally incompatible with
in-*irq usage. Nothing to be done about that.
So NAK on this.
next prev parent reply other threads:[~2018-03-09 17:46 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-05 15:08 Warning from swake_up_all in 4.14.15-rt13 non-RT Corey Minyard
2018-03-06 17:46 ` Sebastian Andrzej Siewior
2018-03-06 22:51 ` Corey Minyard
2018-03-07 15:45 ` Corey Minyard
2018-03-08 17:41 ` Sebastian Andrzej Siewior
2018-03-08 19:54 ` Corey Minyard
2018-03-09 11:04 ` Sebastian Andrzej Siewior
2018-03-09 13:29 ` Corey Minyard
2018-03-09 14:58 ` Sebastian Andrzej Siewior
2018-03-09 16:03 ` Corey Minyard
2018-03-09 17:46 ` Peter Zijlstra [this message]
2018-03-09 20:25 ` Sebastian Andrzej Siewior
2018-03-09 22:26 ` Peter Zijlstra
2018-03-12 10:51 ` Sebastian Andrzej Siewior
2018-03-12 13:27 ` Peter Zijlstra
2018-03-12 14:11 ` Sebastian Andrzej Siewior
2018-03-12 14:29 ` Peter Zijlstra
2018-03-12 19:51 ` Sebastian Andrzej Siewior
2018-03-13 18:40 ` [RT PATCH 1/2] Revert "block: blk-mq: Use swait" Sebastian Andrzej Siewior
2018-03-13 18:42 ` [RT PATCH 2/2] block: blk-mq: move blk_queue_usage_counter_release() into process context Sebastian Andrzej Siewior
2018-03-13 20:10 ` Peter Zijlstra
2018-03-14 15:23 ` Sebastian Andrzej Siewior
2018-03-09 22:02 ` Warning from swake_up_all in 4.14.15-rt13 non-RT Corey Minyard
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