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Subject[PATCH] x86: Fix NULL pointer dereference on CPU hotplug after disabling irqs
In current Linux, percpu variable `vector_irq' is not cleared on offlined
cpus while disabling devices' irqs. If the cpu that has the disabled irqs
in vector_irq is hotplugged, __setup_vector_irq() hits invalid irq vector
and may crash.

This bug can be reproduced as following;
# echo 0 > /sys/devices/system/cpu/cpu7/online
# modprobe -r some_driver_using_interrupts # vector_irq@cpu7 uncleared
# echo 1 > /sys/devices/system/cpu/cpu7/online # kernel may crash
This patch fixes this bug by clearing vector_irq in __clear_irq_vector()
even if the cpu is offlined.

Signed-off-by: Tomoki Sekiyama <tomoki.sekiyama.qu@hitachi.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: linux-kernel@vger.kernel.org
---
arch/x86/kernel/apic/io_apic.c | 4 ++--
1 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
index ac96561..5f0ff59 100644
--- a/arch/x86/kernel/apic/io_apic.c
+++ b/arch/x86/kernel/apic/io_apic.c
@@ -1195,7 +1195,7 @@ static void __clear_irq_vector(int irq, struct irq_cfg *cfg)
BUG_ON(!cfg->vector);
vector = cfg->vector;
- for_each_cpu_and(cpu, cfg->domain, cpu_online_mask)
+ for_each_cpu(cpu, cfg->domain)
per_cpu(vector_irq, cpu)[vector] = -1;
cfg->vector = 0;
@@ -1203,7 +1203,7 @@ static void __clear_irq_vector(int irq, struct irq_cfg *cfg)
if (likely(!cfg->move_in_progress))
return;
- for_each_cpu_and(cpu, cfg->old_domain, cpu_online_mask) {
+ for_each_cpu(cpu, cfg->old_domain) {
for (vector = FIRST_EXTERNAL_VECTOR; vector < NR_VECTORS;
vector++) {
if (per_cpu(vector_irq, cpu)[vector] != irq)
--
1.7.7.6


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