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Subject[PATCH 4.4 324/342] x86/irq: Validate that irq descriptor is still active
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4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Thomas Gleixner <tglx@linutronix.de>

commit 36f34c8c63da3e272fd66f91089228c22d2b6e8b upstream.

In fixup_irqs() we unconditionally dereference the irq chip of an irq
descriptor. The descriptor might still be valid, but already cleaned up,
i.e. the chip removed. Add a check for this condition.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Jiang Liu <jiang.liu@linux.intel.com>
Cc: Joe Lawrence <joe.lawrence@stratus.com>
Cc: Jeremiah Mahler <jmmahler@gmail.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: andy.shevchenko@gmail.com
Cc: Guenter Roeck <linux@roeck-us.net>
Link: http://lkml.kernel.org/r/20151231160106.236423282@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kernel/irq.c b/arch/x86/kernel/irq.c
index f8062aaf5df9..c0b58dd1ca04 100644
--- a/arch/x86/kernel/irq.c
+++ b/arch/x86/kernel/irq.c
@@ -470,6 +470,15 @@ void fixup_irqs(void)
}

chip = irq_data_get_irq_chip(data);
+ /*
+ * The interrupt descriptor might have been cleaned up
+ * already, but it is not yet removed from the radix tree
+ */
+ if (!chip) {
+ raw_spin_unlock(&desc->lock);
+ continue;
+ }
+
if (!irqd_can_move_in_process_context(data) && chip->irq_mask)
chip->irq_mask(data);
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