From: Steven Rostedt <rostedt@goodmis.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>,
linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org,
Thomas Gleixner <tglx@linutronix.de>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: Re: [PATCH 3/7] wait.[ch]: Introduce the simple waitqueue (swait) implementation
Date: Wed, 14 Jan 2015 09:18:49 -0500 [thread overview]
Message-ID: <20150114091849.501a0a72@gandalf.local.home> (raw)
In-Reply-To: <20150114103834.GN23965@worktop.programming.kicks-ass.net>
On Wed, 14 Jan 2015 11:38:34 +0100
Peter Zijlstra <peterz@infradead.org> wrote:
>
>
> So I had a look at this yesterday and came up with the below --
> completely untested etc.
>
> Now in order to compile test I meant to convert the completion code and
> ran head first into complete_all; it uses spin_lock_irqsave() which
> means it can be used from IRQ context. Now if you look at
> __swake_up_all() you'll find a comment on how we cannot have this.
>
> Now I can't remember how important that all was for RT but I figured I'd
> post it and let other people stare at it for a bit.
>
> +/*
> + * Does not allow usage from IRQ disabled, since we must be able to
> + * release IRQs to guarantee bounded hold time.
Actually we (-rt people) don't care if it's done with irq disabled, as
long is it was disabled via spin_lock_irq*() and not
raw_spin_lock_irq() or local_irq_save/disable().
Because in that case, in -rt, irqs would not be disabled. We could add a
check in -rt that makes sure that's the case. I would think this is OK
to call from an interrupt handler as long as it is a thread in -rt.
But, we can keep this restriction for now and change it if we find that
the restriction is preventing us from using it someplace where its
needed for -rt.
> + */
> +void __swake_up_all(struct swait_queue_head *q, unsigned int state)
> +{
> + struct swait_queue *curr, *next;
> + LIST_HEAD(tmp);
> +
> + __swait_wakeup_debug(q, state);
> +
> + if (!swait_active(q))
> + return;
> +
> + raw_spin_lock_irq(&q->lock);
> + list_splice_init(&q->task_list, &tmp);
> + while (!list_empty(&tmp)) {
> + curr = list_first_entry(&tmp, typeof(curr), task_list);
> +
> + wake_up_state(curr->task, state);
> + list_del_init(&curr->task_list);
What happens if curr->task does not match state? We just removed it
from the list and never woke it up, didn't we?
-- Steve
> +
> + if (list_empty(&tmp))
> + break;
> +
> + raw_spin_unlock_irq(&q->lock);
> + raw_spin_lock_irq(&q->lock);
> + }
> + raw_spin_unlock_irq(&q->lock);
> +}
> +EXPORT_SYMBOL(__swake_up_all);
> +
next prev parent reply other threads:[~2015-01-14 14:18 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-18 0:22 [PATCH v2 0/7] simple wait queue support (from -rt) Paul Gortmaker
2014-10-18 0:22 ` [PATCH 1/7] wait.h: mark complex wait functions to prepare for simple wait Paul Gortmaker
2014-10-18 0:22 ` [PATCH 2/7] wait.c: " Paul Gortmaker
2014-10-18 0:22 ` [PATCH 3/7] wait.[ch]: Introduce the simple waitqueue (swait) implementation Paul Gortmaker
2014-10-18 21:34 ` Peter Zijlstra
2014-10-18 23:05 ` Steven Rostedt
2014-10-20 15:21 ` Paul Gortmaker
2014-10-20 15:40 ` Steven Rostedt
2014-10-20 16:05 ` Paul Gortmaker
2014-10-20 16:47 ` Steven Rostedt
2014-10-20 13:44 ` Paul Gortmaker
2015-01-14 10:38 ` Peter Zijlstra
2015-01-14 14:18 ` Steven Rostedt [this message]
2015-01-14 14:31 ` Peter Zijlstra
2015-01-14 15:01 ` Steven Rostedt
2015-01-14 15:29 ` Peter Zijlstra
2014-10-18 0:22 ` [PATCH 4/7] sched/completion: convert completions to use simple wait queues Paul Gortmaker
2014-10-18 0:23 ` [PATCH 5/7] rcu: use simple wait queues where possible in rcutree Paul Gortmaker
2014-10-18 0:23 ` [PATCH 6/7] simplewait: don't run a possibly infinite number of wake under raw lock Paul Gortmaker
2014-10-18 0:23 ` [PATCH 7/7] simplewait: do we make barriers reflect what was in use in -rt? Paul Gortmaker
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