linux-kernel - [PATCH 5/9] x86/irq: place for_each_active

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Date:   Wed, 20 Apr 2022 22:05:17 +0800
From:   Pingfan Liu <kernelfans@...il.com>
To:     x86@...nel.org
Cc:     Pingfan Liu <kernelfans@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "Maciej W. Rozycki" <macro@...am.me.uk>,
        Marc Zyngier <maz@...nel.org>, linux-kernel@...r.kernel.org
Subject: [PATCH 5/9] x86/irq: place for_each_active_irq() in rcu read section

Since there are access to irq_desc, and no preemption is provided at the
involved, it requires rcu read lock to protect irq_desc.

Signed-off-by: Pingfan Liu <kernelfans@...il.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: "Maciej W. Rozycki" <macro@...am.me.uk>
Cc: Marc Zyngier <maz@...nel.org>
Cc: linux-kernel@...r.kernel.org
To: x86@...nel.org
---
 arch/x86/kernel/apic/io_apic.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
index c1bb384935b0..4bb16edcbe4d 100644
--- a/arch/x86/kernel/apic/io_apic.c
+++ b/arch/x86/kernel/apic/io_apic.c
@@ -1333,6 +1333,7 @@ void __init print_IO_APICs(void)
 		print_IO_APIC(ioapic_idx);
 
 	printk(KERN_DEBUG "IRQ to pin mappings:\n");
+	rcu_read_lock();
 	for_each_active_irq(irq) {
 		struct irq_pin_list *entry;
 		struct irq_chip *chip;
@@ -1352,6 +1353,7 @@ void __init print_IO_APICs(void)
 			pr_cont("-> %d:%d", entry->apic, entry->pin);
 		pr_cont("\n");
 	}
+	rcu_read_unlock();
 
 	printk(KERN_INFO ".................................... done.\n");
 }
@@ -2009,6 +2011,7 @@ static inline void init_IO_APIC_traps(void)
 	struct irq_cfg *cfg;
 	unsigned int irq;
 
+	/* The early boot stage is free of irq_desc release */
 	for_each_active_irq(irq) {
 		cfg = irq_cfg(irq);
 		if (IO_APIC_IRQ(irq) && cfg && !cfg->vector) {
-- 
2.31.1