NVMe: Correctly handle IOCTL_SUBMIT_IO when cpus > online queues

nvme_submit_io_cmd() uses smp_processor_id() to pick an IO queue index.
This patch fixes the case where there are more cpus from which the ioctl
call can originate than online queues, which can happen when a device
supports or was allocated fewer interrupt vectors than exist cpu cores.

Thanks to Keith Busch for the implementation suggestion.
Signed-off-by: Sam Bradshaw <sbradshaw@micron.com>
Signed-off-by: Matthew Wilcox <matthew.r.wilcox@intel.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

drivers/block/nvme-core.c

@@ -984,8 +984,8 @@ int nvme_submit_admin_cmd(struct nvme_dev *dev, struct nvme_command *cmd,
 int nvme_submit_io_cmd(struct nvme_dev *dev, struct nvme_command *cmd,
 								u32 *result)
 {
-	return nvme_submit_sync_cmd(dev, smp_processor_id() + 1, cmd, result,
-							NVME_IO_TIMEOUT);
+	return nvme_submit_sync_cmd(dev, this_cpu_read(*dev->io_queue), cmd,
+						result,	NVME_IO_TIMEOUT);
 }
 
 static int nvme_submit_admin_cmd_async(struct nvme_dev *dev,