linux-kernel - Re: [PATCH RT 09/10] drm/i915/gt: Queue and wait for the irq

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Date:   Tue, 23 Nov 2021 10:37:55 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     linux-kernel@...r.kernel.org,
        linux-rt-users <linux-rt-users@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Carsten Emde <C.Emde@...dl.org>,
        John Kacur <jkacur@...hat.com>, Daniel Wagner <wagi@...om.org>,
        Tom Zanussi <zanussi@...nel.org>,
        "Srivatsa S. Bhat" <srivatsa@...il.mit.edu>,
        Clark Williams <williams@...hat.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
Subject: Re: [PATCH RT 09/10] drm/i915/gt: Queue and wait for the irq_work
 item.

On Tue, 23 Nov 2021 09:25:00 +0100
Sebastian Andrzej Siewior <bigeasy@...utronix.de> wrote:

> On 2021-11-22 15:38:56 [-0500], Steven Rostedt wrote:
> > 5.10.78-rt56-rc2 stable review patch.
> > If anyone has any objections, please let me know.  
> 
> I don't mind releasing this as it is but could you please add the
> following irq-work patches:
> 
> * 09089db79859c irq_work: Also rcuwait for !IRQ_WORK_HARD_IRQ on PREEMPT_RT

Is there something else missing here, as this gives the following rejects in
irq_work.c:

--- kernel/irq_work.c
+++ kernel/irq_work.c
@@ -217,7 +217,8 @@ void irq_work_single(void *arg)
         */
        (void)atomic_cmpxchg(&work->node.a_flags, flags, flags & ~IRQ_WORK_BUSY);
 
-       if (!arch_irq_work_has_interrupt())
+       if ((IS_ENABLED(CONFIG_PREEMPT_RT) && !irq_work_is_hard(work)) ||
+           !arch_irq_work_has_interrupt())
                rcuwait_wake_up(&work->irqwait);
 }
 
@@ -277,7 +278,8 @@ void irq_work_sync(struct irq_work *work)
        lockdep_assert_irqs_enabled();
        might_sleep();
 
-       if (!arch_irq_work_has_interrupt()) {
+       if ((IS_ENABLED(CONFIG_PREEMPT_RT) && !irq_work_is_hard(work)) ||
+           !arch_irq_work_has_interrupt()) {
                rcuwait_wait_event(&work->irqwait, !irq_work_is_busy(work),
                                   TASK_UNINTERRUPTIBLE);
                return;

And there's no test here, and no irq_work_is_hard() in 5.10-rt.

This is why I didn't add them.

-- Steve



> * b4c6f86ec2f64 irq_work: Handle some irq_work in a per-CPU thread on PREEMPT_RT
> * 810979682ccc9 irq_work: Allow irq_work_sync() to sleep if irq_work() no IRQ support.
> 
> in a follow-up release?
> 
> Sebastian