disk/aio: Cancel AIO thread on cleanup

If the AIO thread is still calling io_getevents() while the exit path
calls io_destroy(), it will segfault. Wait for the thread to finish before
destroying the context.
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

disk/aio.c

@@ -99,7 +99,6 @@ static void *disk_aio_thread(void *param)
 int disk_aio_setup(struct disk_image *disk)
 {
 	int r;
-	pthread_t thread;
 
 	/* No need to setup AIO if the disk ops won't make use of it */
 	if (!disk->ops->async)
@@ -110,7 +109,7 @@ int disk_aio_setup(struct disk_image *disk)
 		return -errno;
 
 	io_setup(AIO_MAX, &disk->ctx);
-	r = pthread_create(&thread, NULL, disk_aio_thread, disk);
+	r = pthread_create(&disk->thread, NULL, disk_aio_thread, disk);
 	if (r) {
 		r = -errno;
 		close(disk->evt);
@@ -126,6 +125,8 @@ void disk_aio_destroy(struct disk_image *disk)
 	if (!disk->async)
 		return;
 
+	pthread_cancel(disk->thread);
+	pthread_join(disk->thread, NULL);
 	close(disk->evt);
 	io_destroy(disk->ctx);
 }

include/kvm/disk-image.h

@@ -69,6 +69,7 @@ struct disk_image {
 #ifdef CONFIG_HAS_AIO
 	io_context_t			ctx;
 	int				evt;
+	pthread_t			thread;
 #endif /* CONFIG_HAS_AIO */
 	const char			*wwpn;
 	const char			*tpgt;