linux-kernel - Re: [PATCH RT 2/3] irq_work: Fix checking of IRQ_WORK_LAZY flag set on non PREEMPT

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Message-ID: <20200403215504.GA30386@duo.ucw.cz>
Date:   Fri, 3 Apr 2020 23:55:05 +0200
From:   Pavel Machek <pavel@...x.de>
To:     Daniel Wagner <wagi@...om.org>
Cc:     Pavel Machek <pavel@...x.de>, Steven Rostedt <rostedt@...dmis.org>,
        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>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        John Kacur <jkacur@...hat.com>,
        Julia Cartwright <julia@...com>,
        Tom Zanussi <zanussi@...nel.org>,
        "Srivatsa S. Bhat" <srivatsa@...il.mit.edu>
Subject: Re: [PATCH RT 2/3] irq_work: Fix checking of IRQ_WORK_LAZY flag set
 on non PREEMPT_RT

Hi!

> On Thu, Apr 02, 2020 at 07:22:49PM +0200, Pavel Machek wrote:
> > I'm currently playing with 4.4.X branch, but I'll eventually test it.
> > 
> > Is it possible that 4.4.X branch needs similar patch? My code review
> > suggests so...
> 
> I was waiting for Steven to post the final patch. I'll pick it up for
> the next v4.4-rt release.

It will not apply cleanly...

Here is version that applies to 4.4, and should compile. Not sure what
other branches it should be applied to.

Best regards,
								Pavel

-- cut --

From: "Steven Rostedt (VMware)" <rostedt@...dmis.org>
    
When CONFIG_PREEMPT_RT_FULL is not set, some of the checks for using
lazy_list are not properly made as the IRQ_WORK_LAZY is not checked. There's
two locations that need this update, so a use_lazy_list() helper function is
added and used in both locations.
    
Link: https://lore.kernel.org/r/20200321230028.GA22058@duo.ucw.cz
Reported-by: Pavel Machek <pavel@...x.de>
Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
[ported to 4.4]
Signed-off-by: Pavel Machek <pavel@...x.de>

diff --git a/kernel/irq_work.c b/kernel/irq_work.c
index 2899ba0d23d1..abc65de5d793 100644
--- a/kernel/irq_work.c
+++ b/kernel/irq_work.c
@@ -57,6 +57,12 @@ void __weak arch_irq_work_raise(void)
 	 */
 }
 
+static inline bool use_lazy_list(struct irq_work *work)
+{
+	return (IS_ENABLED(CONFIG_PREEMPT_RT_FULL) && !(work->flags & IRQ_WORK_HARD_IRQ))
+		|| (work->flags & IRQ_WORK_LAZY);
+}
+
 #ifdef CONFIG_SMP
 /*
  * Enqueue the irq_work @work on @cpu unless it's already pending
@@ -78,7 +84,7 @@ bool irq_work_queue_on(struct irq_work *work, int cpu)
 	if (!irq_work_claim(work))
 		return false;
 
-	if (IS_ENABLED(CONFIG_PREEMPT_RT_FULL) && !(work->flags & IRQ_WORK_HARD_IRQ))
+	if (use_lazy_list(work))
 		list = &per_cpu(lazy_list, cpu);
 	else
 		list = &per_cpu(raised_list, cpu);
@@ -95,7 +101,7 @@ EXPORT_SYMBOL_GPL(irq_work_queue_on);
 bool irq_work_queue(struct irq_work *work)
 {
 	struct llist_head *list;
-	bool lazy_work, realtime = IS_ENABLED(CONFIG_PREEMPT_RT_FULL);
+	int lazy_work;
 
 	/* Only queue if not already pending */
 	if (!irq_work_claim(work))
@@ -106,7 +112,7 @@ bool irq_work_queue(struct irq_work *work)
 
 	lazy_work = work->flags & IRQ_WORK_LAZY;
 
-	if (lazy_work || (realtime && !(work->flags & IRQ_WORK_HARD_IRQ)))
+	if (use_lazy_list(work))
 		list = this_cpu_ptr(&lazy_list);
 	else
 		list = this_cpu_ptr(&raised_list);

-- 
DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany

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