lib: cpu_rmap: Add irq_cpu_rmap_remove to complement irq_cpu_rmap_add

Add a function to complement irq_cpu_rmap_add(). It removes the irq from
the reverse mapping by setting the notifier to NULL. The function calls
irq_set_affinity_notifier() with NULL at the notify argument which then
cancel any pending notifier work and decrement reference on the
notifier. When ref count reaches zero, the glue pointer is kfree and the
rmap entry is set to NULL serving both to avoid second attempt to
release it and also making the rmap entry available for subsequent
mapping.

It should be noted the drivers usually creates the reverse mapping at
initialization time and remove it at unload time so we do not expect
failures in allocating rmap due to kref holding the glue entry.

Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Eli Cohen <elic@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>

include/linux/cpu_rmap.h

@@ -60,6 +60,7 @@ static inline struct cpu_rmap *alloc_irq_cpu_rmap(unsigned int size)
 }
 extern void free_irq_cpu_rmap(struct cpu_rmap *rmap);
 
+int irq_cpu_rmap_remove(struct cpu_rmap *rmap, int irq);
 extern int irq_cpu_rmap_add(struct cpu_rmap *rmap, int irq);
 
 #endif /* __LINUX_CPU_RMAP_H */

lib/cpu_rmap.c

@@ -285,6 +285,17 @@ static void irq_cpu_rmap_release(struct kref *ref)
 	kfree(glue);
 }
 
+/**
+ * irq_cpu_rmap_remove - remove an IRQ from a CPU affinity reverse-map
+ * @rmap: The reverse-map
+ * @irq: The IRQ number
+ */
+int irq_cpu_rmap_remove(struct cpu_rmap *rmap, int irq)
+{
+	return irq_set_affinity_notifier(irq, NULL);
+}
+EXPORT_SYMBOL(irq_cpu_rmap_remove);
+
 /**
  * irq_cpu_rmap_add - add an IRQ to a CPU affinity reverse-map
  * @rmap: The reverse-map