mshv: clear eventfd counter on irqfd shutdown

While unhooking from the irqfd waitqueue, clear the internal eventfd
counter by using eventfd_ctx_remove_wait_queue() instead of
remove_wait_queue(), preventing potential spurious interrupts. This
removes the need to store a pointer into the workqueue, as the eventfd
already keeps track of it.

This mimicks what other similar subsystems do on their equivalent paths
with their irqfds (KVM, Xen, ACRN support, etc).

Signed-off-by: Carlos López <[e-mail]>
Signed-off-by: Wei Liu <[e-mail]>

drivers/hv/mshv_eventfd.c

···
 {
 	struct mshv_irqfd *irqfd =
 			container_of(work, struct mshv_irqfd, irqfd_shutdown);
+	u64 cnt;
 
 	/*
 	 * Synchronize with the wait-queue and unhook ourselves to prevent
 	 * further events.
 	 */
-	remove_wait_queue(irqfd->irqfd_wqh, &irqfd->irqfd_wait);
+	eventfd_ctx_remove_wait_queue(irqfd->irqfd_eventfd_ctx, &irqfd->irqfd_wait, &cnt);
 
 	if (irqfd->irqfd_resampler) {
 		mshv_irqfd_resampler_shutdown(irqfd);
···
 {
 	struct mshv_irqfd *irqfd =
 			container_of(polltbl, struct mshv_irqfd, irqfd_polltbl);
-
-	irqfd->irqfd_wqh = wqh;
 
 	/*
 	 * TODO: Ensure there isn't already an exclusive, priority waiter, e.g.

drivers/hv/mshv_eventfd.h

···
 	struct mshv_lapic_irq		     irqfd_lapic_irq;
 	struct hlist_node		     irqfd_hnode;
 	poll_table			     irqfd_polltbl;
-	wait_queue_head_t		    *irqfd_wqh;
 	wait_queue_entry_t		     irqfd_wait;
 	struct work_struct		     irqfd_shutdown;
 	struct mshv_irqfd_resampler	    *irqfd_resampler;