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From:   Shanker Donthineni <sdonthineni@nvidia.com>
To:     Thomas Gleixner <tglx@linutronix.de>, Marc Zyngier <maz@kernel.org>
CC:     Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Michael Walle <michael@walle.cc>,
        Shanker Donthineni <sdonthineni@nvidia.com>,
        <linux-kernel@vger.kernel.org>, Vikram Sethi <vsethi@nvidia.com>,
        "Liam R . Howlett" <Liam.Howlett@oracle.com>
Subject: [PATCH v2 1/3] genirq: Use hlist for managing resend handlers
Date:   Sat, 8 Apr 2023 12:15:24 -0500
Message-ID: <20230408171526.3059039-2-sdonthineni@nvidia.com>
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The current implementation utilizes a bitmap for managing IRQ resend
handlers, which is allocated based on the SPARSE_IRQ/NR_IRQS macros.
However, this method may not efficiently utilize memory during runtime,
particularly when IRQ_BITMAP_BITS is large.

This proposed patch aims to address this issue by using hlist to manage
IRQ resend handlers instead of relying on static memory allocation.
Additionally, a new function, clear_irq_resend(), is introduced and
called from irq_shutdown to ensure a graceful teardown of IRQD.

Signed-off-by: Shanker Donthineni <sdonthineni@nvidia.com>
---
 include/linux/irqdesc.h |  3 +++
 kernel/irq/chip.c       |  1 +
 kernel/irq/internals.h  |  1 +
 kernel/irq/irqdesc.c    |  6 ++++++
 kernel/irq/resend.c     | 41 ++++++++++++++++++++++++-----------------
 5 files changed, 35 insertions(+), 17 deletions(-)

diff --git a/include/linux/irqdesc.h b/include/linux/irqdesc.h
index 844a8e30e6de..d9451d456a73 100644
--- a/include/linux/irqdesc.h
+++ b/include/linux/irqdesc.h
@@ -102,6 +102,9 @@ struct irq_desc {
 	int			parent_irq;
 	struct module		*owner;
 	const char		*name;
+#ifdef CONFIG_HARDIRQS_SW_RESEND
+	struct hlist_node	resend_node;
+#endif
 } ____cacheline_internodealigned_in_smp;
 
 #ifdef CONFIG_SPARSE_IRQ
diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
index 49e7bc871fec..2eac5532c3c8 100644
--- a/kernel/irq/chip.c
+++ b/kernel/irq/chip.c
@@ -306,6 +306,7 @@ static void __irq_disable(struct irq_desc *desc, bool mask);
 void irq_shutdown(struct irq_desc *desc)
 {
 	if (irqd_is_started(&desc->irq_data)) {
+		clear_irq_resend(desc);
 		desc->depth = 1;
 		if (desc->irq_data.chip->irq_shutdown) {
 			desc->irq_data.chip->irq_shutdown(&desc->irq_data);
diff --git a/kernel/irq/internals.h b/kernel/irq/internals.h
index 5fdc0b557579..2fd17057ed4b 100644
--- a/kernel/irq/internals.h
+++ b/kernel/irq/internals.h
@@ -113,6 +113,7 @@ irqreturn_t handle_irq_event(struct irq_desc *desc);
 
 /* Resending of interrupts :*/
 int check_irq_resend(struct irq_desc *desc, bool inject);
+void clear_irq_resend(struct irq_desc *desc);
 bool irq_wait_for_poll(struct irq_desc *desc);
 void __irq_wake_thread(struct irq_desc *desc, struct irqaction *action);
 
diff --git a/kernel/irq/irqdesc.c b/kernel/irq/irqdesc.c
index 240e145e969f..47543b5a0edb 100644
--- a/kernel/irq/irqdesc.c
+++ b/kernel/irq/irqdesc.c
@@ -415,6 +415,9 @@ static struct irq_desc *alloc_desc(int irq, int node, unsigned int flags,
 	desc_set_defaults(irq, desc, node, affinity, owner);
 	irqd_set(&desc->irq_data, flags);
 	kobject_init(&desc->kobj, &irq_kobj_type);
+#ifdef CONFIG_HARDIRQS_SW_RESEND
+	INIT_HLIST_NODE(&desc->resend_node);
+#endif
 
 	return desc;
 
@@ -581,6 +584,9 @@ int __init early_irq_init(void)
 		mutex_init(&desc[i].request_mutex);
 		init_waitqueue_head(&desc[i].wait_for_threads);
 		desc_set_defaults(i, &desc[i], node, NULL, NULL);
+#ifdef CONFIG_HARDIRQS_SW_RESEND
+		INIT_HLIST_NODE(&desc->resend_node);
+#endif
 	}
 	return arch_early_irq_init();
 }
diff --git a/kernel/irq/resend.c b/kernel/irq/resend.c
index 0c46e9fe3a89..d3db2628a720 100644
--- a/kernel/irq/resend.c
+++ b/kernel/irq/resend.c
@@ -21,8 +21,9 @@
 
 #ifdef CONFIG_HARDIRQS_SW_RESEND
 
-/* Bitmap to handle software resend of interrupts: */
-static DECLARE_BITMAP(irqs_resend, IRQ_BITMAP_BITS);
+/* hlist_head to handle software resend of interrupts: */
+static HLIST_HEAD(irq_resend_list);
+static DEFINE_RAW_SPINLOCK(irq_resend_lock);
 
 /*
  * Run software resends of IRQ's
@@ -30,18 +31,17 @@ static DECLARE_BITMAP(irqs_resend, IRQ_BITMAP_BITS);
 static void resend_irqs(struct tasklet_struct *unused)
 {
 	struct irq_desc *desc;
-	int irq;
-
-	while (!bitmap_empty(irqs_resend, nr_irqs)) {
-		irq = find_first_bit(irqs_resend, nr_irqs);
-		clear_bit(irq, irqs_resend);
-		desc = irq_to_desc(irq);
-		if (!desc)
-			continue;
-		local_irq_disable();
+
+	raw_spin_lock_irq(&irq_resend_lock);
+	while (!hlist_empty(&irq_resend_list)) {
+		desc = hlist_entry(irq_resend_list.first, struct irq_desc,
+				   resend_node);
+		hlist_del_init(&desc->resend_node);
+		raw_spin_unlock(&irq_resend_lock);
 		desc->handle_irq(desc);
-		local_irq_enable();
+		raw_spin_lock(&irq_resend_lock);
 	}
+	raw_spin_unlock_irq(&irq_resend_lock);
 }
 
 /* Tasklet to handle resend: */
@@ -49,8 +49,6 @@ static DECLARE_TASKLET(resend_tasklet, resend_irqs);
 
 static int irq_sw_resend(struct irq_desc *desc)
 {
-	unsigned int irq = irq_desc_get_irq(desc);
-
 	/*
 	 * Validate whether this interrupt can be safely injected from
 	 * non interrupt context
@@ -70,16 +68,25 @@ static int irq_sw_resend(struct irq_desc *desc)
 		 */
 		if (!desc->parent_irq)
 			return -EINVAL;
-		irq = desc->parent_irq;
 	}
 
-	/* Set it pending and activate the softirq: */
-	set_bit(irq, irqs_resend);
+	/* Add to resend_list and activate the softirq: */
+	raw_spin_lock(&irq_resend_lock);
+	hlist_add_head(&desc->resend_node, &irq_resend_list);
+	raw_spin_unlock(&irq_resend_lock);
 	tasklet_schedule(&resend_tasklet);
 	return 0;
 }
 
+void clear_irq_resend(struct irq_desc *desc)
+{
+	raw_spin_lock(&irq_resend_lock);
+	hlist_del_init(&desc->resend_node);
+	raw_spin_unlock(&irq_resend_lock);
+}
 #else
+void clear_irq_resend(struct irq_desc *desc) {}
+
 static int irq_sw_resend(struct irq_desc *desc)
 {
 	return -EINVAL;
-- 
2.25.1