[PATCH] x86/ioapic: Fix NULL pointer dereference on CPU hotplug after disabling irqs

[Tomoki Sekiyama <tomoki.sekiyama.qu@hitachi.com>]

Hi,

In current Linux, percpu variable `vector_irq' is not always cleared when
a CPU is offlined. If the cpu that has the disabled irqs in vector_irq is
hotplugged again, __setup_vector_irq() hits invalid irq vector and may
crash.

Commit f6175f5bfb4c partially fixes this, but was not enough in
environments with IOMMU IRQ remapper.

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 __fixup_irqs() when
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: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: Alexander Gordeev <agordeev@redhat.com>
---
 arch/x86/kernel/irq.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/irq.c b/arch/x86/kernel/irq.c
index 3dafc60..d27b27d 100644
--- a/arch/x86/kernel/irq.c
+++ b/arch/x86/kernel/irq.c
@@ -328,6 +328,7 @@ void fixup_irqs(void)
 				chip->irq_retrigger(data);
 			raw_spin_unlock(&desc->lock);
 		}
+		__this_cpu_write(vector_irq[vector], -1);
 	}
 }
 #endif
-- 
1.7.7.6
-- 
Tomoki Sekiyama <tomoki.sekiyama.qu@hitachi.com>
Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory