genirq: Provide irq_fixup_move_pending()

If an CPU goes offline, the interrupts are migrated away, but a eventually
pending interrupt move, which has not yet been made effective is kept
pending even if the outgoing CPU is the sole target of the pending affinity
mask. What's worse is, that the pending affinity mask is discarded even if
it would contain a valid subset of the online CPUs.

Implement a helper function which allows to avoid these issues.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Keith Busch <keith.busch@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Christoph Hellwig <hch@lst.de>
Link: http://lkml.kernel.org/r/20170619235444.691345468@linutronix.de

diff --git a/include/linux/irq.h b/include/linux/irq.h
index 7e62e10..d008065 100644
--- a/include/linux/irq.h
+++ b/include/linux/irq.h
@@ -491,9 +491,14 @@ extern void irq_migrate_all_off_this_cpu(void);
 #if defined(CONFIG_SMP) && defined(CONFIG_GENERIC_PENDING_IRQ)
 void irq_move_irq(struct irq_data *data);
 void irq_move_masked_irq(struct irq_data *data);
+bool irq_fixup_move_pending(struct irq_desc *desc, bool force_clear);
 #else
 static inline void irq_move_irq(struct irq_data *data) { }
 static inline void irq_move_masked_irq(struct irq_data *data) { }
+static inline bool irq_fixup_move_pending(struct irq_desc *desc, bool fclear)
+{
+	return false;
+}
 #endif
 
 extern int no_irq_affinity;