free_irq() does not disable/mask the irq, in case disable or shutdown in struct 
irq_chip is left uninitilazied.

/**
 * struct irq_chip - hardware interrupt chip descriptor
 *
 * @name:               name for /proc/interrupts
 * @startup:            start up the interrupt (defaults to ->enable if NULL)
 * @shutdown:           shut down the interrupt (defaults to ->disable if NULL)
 * @enable:             enable the interrupt (defaults to chip->unmask if NULL)
 * @disable:            disable the interrupt (defaults to chip->mask if NULL)


According to linux/irq.h struct irq_chip information,
chip->disable should default to chip->mask if NULL.
However irq_chip_set_defaults(struct irq_chip *chip) will set it to 
default_disable a empty function.


Looking through various architectures, it's pretty common that disable and 
shutdown is NULL.
So this bug affects many architectures.

This patch fixes the issue.

Best regards,
Michael

Index: irq/chip.c
===================================================================
--- irq/chip.c  (revision 4276)
+++ irq/chip.c  (working copy)
@@ -233,6 +233,10 @@
  */
 static void default_disable(unsigned int irq)
 {
+       struct irq_desc *desc = irq_desc + irq;
+
+       desc->chip->mask(irq);
+       desc->status |= IRQ_MASKED;
 }

 /*


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