mmc: core: block: fix sloppy typing in mmc_blk_ioctl_multi_cmd()

Despite mmc_ioc_multi_cmd::num_of_cmds is a 64-bit field, its maximum
value is limited to MMC_IOC_MAX_CMDS (only 255); using a 64-bit local
variable to hold a copy of that field leads to gcc generating ineffective
loop code: despite the source code using an *int* variable for the loop
counters, the 32-bit object code uses 64-bit unsigned counters. Also,
gcc has to drop the most significant word of that 64-bit variable when
calling kcalloc() and assigning to mmc_queue_req::ioc_count anyway.
Using the *unsigned int* variable instead results in a better code.

Found by Linux Verification Center (linuxtesting.org) with the SVACE static
analysis tool.

Signed-off-by: Sergey Shtylyov <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Ulf Hansson <[e-mail]>

drivers/mmc/core/block.c

···
 	struct mmc_ioc_cmd __user *cmds = user->cmds;
 	struct mmc_card *card;
 	struct mmc_queue *mq;
-	int i, err = 0, ioc_err = 0;
+	int err = 0, ioc_err = 0;
 	__u64 num_of_cmds;
+	unsigned int i, n;
 	struct request *req;
 
 	if (copy_from_user(&num_of_cmds, &user->num_of_cmds,
···
 	if (num_of_cmds > MMC_IOC_MAX_CMDS)
 		return -EINVAL;
 
-	idata = kcalloc(num_of_cmds, sizeof(*idata), GFP_KERNEL);
+	n = num_of_cmds;
+	idata = kcalloc(n, sizeof(*idata), GFP_KERNEL);
 	if (!idata)
 		return -ENOMEM;
 
-	for (i = 0; i < num_of_cmds; i++) {
+	for (i = 0; i < n; i++) {
 		idata[i] = mmc_blk_ioctl_copy_from_user(&cmds[i]);
 		if (IS_ERR(idata[i])) {
 			err = PTR_ERR(idata[i]);
-			num_of_cmds = i;
+			n = i;
 			goto cmd_err;
 		}
 		/* This will be NULL on non-RPMB ioctl():s */
···
 	req_to_mmc_queue_req(req)->drv_op =
 		rpmb ? MMC_DRV_OP_IOCTL_RPMB : MMC_DRV_OP_IOCTL;
 	req_to_mmc_queue_req(req)->drv_op_data = idata;
-	req_to_mmc_queue_req(req)->ioc_count = num_of_cmds;
+	req_to_mmc_queue_req(req)->ioc_count = n;
 	blk_execute_rq(req, false);
 	ioc_err = req_to_mmc_queue_req(req)->drv_op_result;
 
 	/* copy to user if data and response */
-	for (i = 0; i < num_of_cmds && !err; i++)
+	for (i = 0; i < n && !err; i++)
 		err = mmc_blk_ioctl_copy_to_user(&cmds[i], idata[i]);
 
 	blk_mq_free_request(req);
 
 cmd_err:
-	for (i = 0; i < num_of_cmds; i++) {
+	for (i = 0; i < n; i++) {
 		kfree(idata[i]->buf);
 		kfree(idata[i]);
 	}