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

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Message-Id: <20200331163513.674653275@goodmis.org>
Date:   Tue, 31 Mar 2020 12:34:55 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     linux-kernel@...r.kernel.org,
        linux-rt-users <linux-rt-users@...r.kernel.org>
Cc:     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>,
        Daniel Wagner <wagi@...om.org>,
        Tom Zanussi <zanussi@...nel.org>,
        "Srivatsa S. Bhat" <srivatsa@...il.mit.edu>,
        Pavel Machek <pavel@...x.de>
Subject: [PATCH RT 2/3] irq_work: Fix checking of IRQ_WORK_LAZY flag set on non PREEMPT_RT

4.19.106-rt46-rc1 stable review patch.
If anyone has any objections, please let me know.

------------------

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>
---
 kernel/irq_work.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/kernel/irq_work.c b/kernel/irq_work.c
index 2940622da5b3..b6d9d35941ac 100644
--- a/kernel/irq_work.c
+++ b/kernel/irq_work.c
@@ -70,6 +70,12 @@ static void __irq_work_queue_local(struct irq_work *work, struct llist_head *lis
 		arch_irq_work_raise();
 }
 
+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);
+}
+
 /* Enqueue the irq work @work on the current CPU */
 bool irq_work_queue(struct irq_work *work)
 {
@@ -81,11 +87,10 @@ bool irq_work_queue(struct irq_work *work)
 
 	/* Queue the entry and raise the IPI if needed. */
 	preempt_disable();
-	if (IS_ENABLED(CONFIG_PREEMPT_RT_FULL) && !(work->flags & IRQ_WORK_HARD_IRQ))
+	if (use_lazy_list(work))
 		list = this_cpu_ptr(&lazy_list);
 	else
 		list = this_cpu_ptr(&raised_list);
-
 	__irq_work_queue_local(work, list);
 	preempt_enable();
 
@@ -106,7 +111,6 @@ bool irq_work_queue_on(struct irq_work *work, int cpu)
 
 #else /* CONFIG_SMP: */
 	struct llist_head *list;
-	bool lazy_work, realtime = IS_ENABLED(CONFIG_PREEMPT_RT_FULL);
 
 	/* All work should have been flushed before going offline */
 	WARN_ON_ONCE(cpu_is_offline(cpu));
@@ -116,10 +120,7 @@ bool irq_work_queue_on(struct irq_work *work, int cpu)
 		return false;
 
 	preempt_disable();
-
-	lazy_work = work->flags & IRQ_WORK_LAZY;
-
-	if (lazy_work || (realtime && !(work->flags & IRQ_WORK_HARD_IRQ)))
+	if (use_lazy_list(work))
 		list = &per_cpu(lazy_list, cpu);
 	else
 		list = &per_cpu(raised_list, cpu);
-- 
2.25.1