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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: linux-kernel@vger.kernel.org,
	linux-rt-users <linux-rt-users@vger.kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Carsten Emde <C.Emde@osadl.org>, John Kacur <jkacur@redhat.com>,
	Daniel Wagner <wagi@monom.org>, Tom Zanussi <zanussi@kernel.org>,
	"Srivatsa S . Bhat" <srivatsa@csail.mit.edu>,
	Clark Williams <williams@redhat.com>,
	Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
	bigeasy@linutronix.de
Subject: [PATCH RT 1/3] irq_work: Allow irq_work_sync() to sleep if irq_work() no IRQ support.
Date: Wed, 24 Nov 2021 17:12:19 +0100	[thread overview]
Message-ID: <20211124161221.2224005-2-bigeasy@linutronix.de> (raw)
In-Reply-To: <20211124161221.2224005-1-bigeasy@linutronix.de>

irq_work() triggers instantly an interrupt if supported by the
architecture. Otherwise the work will be processed on the next timer
tick. In worst case irq_work_sync() could spin up to a jiffy.

irq_work_sync() is usually used in tear down context which is fully
preemptible. Based on review irq_work_sync() is invoked from preemptible
context and there is one waiter at a time. This qualifies it to use
rcuwait for synchronisation.

Let irq_work_sync() synchronize with rcuwait if the architecture
processes irqwork via the timer tick.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20211006111852.1514359-3-bigeasy@linutronix.de
---
 include/linux/irq_work.h | 10 +++++++++-
 kernel/irq_work.c        | 10 ++++++++++
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/include/linux/irq_work.h b/include/linux/irq_work.h
index f941f2d7d71ce..3c6d3a96bca0f 100644
--- a/include/linux/irq_work.h
+++ b/include/linux/irq_work.h
@@ -3,6 +3,7 @@
 #define _LINUX_IRQ_WORK_H
 
 #include <linux/smp_types.h>
+#include <linux/rcuwait.h>
 
 /*
  * An entry can be in one of four states:
@@ -22,6 +23,7 @@ struct irq_work {
 		};
 	};
 	void (*func)(struct irq_work *);
+	struct rcuwait irqwait;
 };
 
 static inline
@@ -29,13 +31,19 @@ void init_irq_work(struct irq_work *work, void (*func)(struct irq_work *))
 {
 	atomic_set(&work->flags, 0);
 	work->func = func;
+	rcuwait_init(&work->irqwait);
 }
 
 #define DEFINE_IRQ_WORK(name, _f) struct irq_work name = {	\
 		.flags = ATOMIC_INIT(0),			\
-		.func  = (_f)					\
+		.func  = (_f),					\
+		.irqwait = __RCUWAIT_INITIALIZER(irqwait),	\
 }
 
+static inline bool irq_work_is_busy(struct irq_work *work)
+{
+	return atomic_read(&work->flags) & IRQ_WORK_BUSY;
+}
 
 bool irq_work_queue(struct irq_work *work);
 bool irq_work_queue_on(struct irq_work *work, int cpu);
diff --git a/kernel/irq_work.c b/kernel/irq_work.c
index 8183d30e1bb1c..8969aff790e21 100644
--- a/kernel/irq_work.c
+++ b/kernel/irq_work.c
@@ -165,6 +165,9 @@ void irq_work_single(void *arg)
 	 */
 	flags &= ~IRQ_WORK_PENDING;
 	(void)atomic_cmpxchg(&work->flags, flags, flags & ~IRQ_WORK_BUSY);
+
+	if (!arch_irq_work_has_interrupt())
+		rcuwait_wake_up(&work->irqwait);
 }
 
 static void irq_work_run_list(struct llist_head *list)
@@ -231,6 +234,13 @@ void irq_work_tick_soft(void)
 void irq_work_sync(struct irq_work *work)
 {
 	lockdep_assert_irqs_enabled();
+	might_sleep();
+
+	if (!arch_irq_work_has_interrupt()) {
+		rcuwait_wait_event(&work->irqwait, !irq_work_is_busy(work),
+				   TASK_UNINTERRUPTIBLE);
+		return;
+	}
 
 	while (atomic_read(&work->flags) & IRQ_WORK_BUSY)
 		cpu_relax();
-- 
2.34.0


  reply	other threads:[~2021-11-24 16:12 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-11-22 20:38 [PATCH RT 00/10] Linux 5.10.78-rt56-rc2 Steven Rostedt
2021-11-22 20:38 ` [PATCH RT 01/10] mm, zsmalloc: Convert zsmalloc_handle.lock to spinlock_t Steven Rostedt
2021-11-22 20:38 ` [PATCH RT 02/10] sched: Fix get_push_task() vs migrate_disable() Steven Rostedt
2021-11-22 20:38 ` [PATCH RT 03/10] sched: Switch wait_task_inactive to HRTIMER_MODE_REL_HARD Steven Rostedt
2021-11-22 20:38 ` [PATCH RT 04/10] preempt: Move preempt_enable_no_resched() to the RT block Steven Rostedt
2021-11-22 20:38 ` [PATCH RT 05/10] mm: Disable NUMA_BALANCING_DEFAULT_ENABLED and TRANSPARENT_HUGEPAGE on PREEMPT_RT Steven Rostedt
2021-11-22 20:38 ` [PATCH RT 06/10] fscache: Use only one fscache_object_cong_wait Steven Rostedt
2021-11-22 20:38 ` [PATCH RT 07/10] fscache: Use only one fscache_object_cong_wait (2) Steven Rostedt
2021-11-22 20:38 ` [PATCH RT 08/10] locking: Drop might_resched() from might_sleep_no_state_check() Steven Rostedt
2021-11-22 20:38 ` [PATCH RT 09/10] drm/i915/gt: Queue and wait for the irq_work item Steven Rostedt
2021-11-23  8:25   ` Sebastian Andrzej Siewior
2021-11-23 15:37     ` Steven Rostedt
2021-11-24 16:12       ` Sebastian Andrzej Siewior
2021-11-24 16:12         ` Sebastian Andrzej Siewior [this message]
2021-11-24 16:12         ` [PATCH RT 2/3] irq_work: Handle some irq_work in a per-CPU thread on PREEMPT_RT Sebastian Andrzej Siewior
2021-11-24 16:12         ` [PATCH RT 3/3] irq_work: Also rcuwait for !IRQ_WORK_HARD_IRQ " Sebastian Andrzej Siewior
2021-11-22 20:38 ` [PATCH RT 10/10] Linux 5.10.78-rt56-rc2 Steven Rostedt

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