linux-kernel - [PATCH] x86: irq: Check for valid irq descriptor in check_irq_vectors_for_cpu

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Date:	Wed, 4 Feb 2015 14:27:54 +0100
From:	Joerg Roedel <jroedel@...e.de>
To:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Prarit Bhargava <prarit@...hat.com>,
	Yinghai Lu <yinghai@...nel.org>,
	Jiang Liu <jiang.liu@...ux.intel.com>
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org, alnovak@...e.com,
	jroedel@...e.de, joro@...tes.org
Subject: [PATCH] x86: irq: Check for valid irq descriptor in
 check_irq_vectors_for_cpu_disable

Hi,

here is a patch to fix a kernel panic at shutdown we have seen recently.
The issue is hard to reproduce, so the patch description about the root
cause of the bug comes only from review and my current understanding of
x86 irq code.

So if what I wrote in the patch description doesn't make sense, please
let me know.

Constructive comments and feedback welcome.

Thanks,

	Joerg

>From 153e8f6cf39c42dd9767eb49a27eacfb69738fb0 Mon Sep 17 00:00:00 2001
From: Joerg Roedel <jroedel@...e.de>
Date: Wed, 4 Feb 2015 13:33:33 +0100
Subject: [PATCH] x86: irq: Check for valid irq descriptor in
 check_irq_vectors_for_cpu_disable

When an interrupt is migrated away from a cpu it will stay
in its vector_irq array until smp_irq_move_cleanup_interrupt
succeeded. The cfg->move_in_progress flag is cleared already
when the IPI was sent.

When the interrupt is destroyed after migration its 'struct
irq_desc' is freed and the vector_irq arrays are cleaned up.
But since cfg->move_in_progress is already 0 the references
at cpus before the last migration will not be cleared. So
this would leave a reference to an already destroyed irq
alive.

When the cpu is taken down at this point, the
check_irq_vectors_for_cpu_disable function finds a valid irq
number in the vector_irq array, but gets NULL for its
descriptor and dereferences it, causing a kernel panic.

This has been observed on real systems at shutdown. Add a
check to check_irq_vectors_for_cpu_disable for a valid
'struct irq_desc' to prevent this issue.

Signed-off-by: Joerg Roedel <jroedel@...e.de>
---
 arch/x86/kernel/irq.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kernel/irq.c b/arch/x86/kernel/irq.c
index 705ef8d..67b1cbe 100644
--- a/arch/x86/kernel/irq.c
+++ b/arch/x86/kernel/irq.c
@@ -302,6 +302,9 @@ int check_irq_vectors_for_cpu_disable(void)
 		irq = __this_cpu_read(vector_irq[vector]);
 		if (irq >= 0) {
 			desc = irq_to_desc(irq);
+			if (!desc)
+				continue;
+
 			data = irq_desc_get_irq_data(desc);
 			cpumask_copy(&affinity_new, data->affinity);
 			cpu_clear(this_cpu, affinity_new);
-- 
1.8.4.5

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