md/raid10: optimize fix_read_error

We dereference r10_bio->read_slot too many times in fix_read_error().
Optimize it by using a variable to store read_slot.
Signed-off-by: Li Nan <linan122@huawei.com>
Reviewed-by: Yu Kuai <yukuai3@huawei.com>
Link: https://lore.kernel.org/r/20230623173236.2513554-2-linan666@huaweicloud.comSigned-off-by: Song Liu <song@kernel.org>

drivers/md/raid10.c

@@ -2718,10 +2718,10 @@ static int r10_sync_page_io(struct md_rdev *rdev, sector_t sector,
 static void fix_read_error(struct r10conf *conf, struct mddev *mddev, struct r10bio *r10_bio)
 {
 	int sect = 0; /* Offset from r10_bio->sector */
-	int sectors = r10_bio->sectors;
+	int sectors = r10_bio->sectors, slot = r10_bio->read_slot;
 	struct md_rdev *rdev;
 	int max_read_errors = atomic_read(&mddev->max_corr_read_errors);
-	int d = r10_bio->devs[r10_bio->read_slot].devnum;
+	int d = r10_bio->devs[slot].devnum;
 
 	/* still own a reference to this rdev, so it cannot
 	 * have been cleared recently.
@@ -2742,13 +2742,13 @@ static void fix_read_error(struct r10conf *conf, struct mddev *mddev, struct r10
 		pr_notice("md/raid10:%s: %pg: Failing raid device\n",
 			  mdname(mddev), rdev->bdev);
 		md_error(mddev, rdev);
-		r10_bio->devs[r10_bio->read_slot].bio = IO_BLOCKED;
+		r10_bio->devs[slot].bio = IO_BLOCKED;
 		return;
 	}
 
 	while(sectors) {
 		int s = sectors;
-		int sl = r10_bio->read_slot;
+		int sl = slot;
 		int success = 0;
 		int start;
 
@@ -2783,7 +2783,7 @@ static void fix_read_error(struct r10conf *conf, struct mddev *mddev, struct r10
 			sl++;
 			if (sl == conf->copies)
 				sl = 0;
-		} while (!success && sl != r10_bio->read_slot);
+		} while (!success && sl != slot);
 		rcu_read_unlock();
 
 		if (!success) {
@@ -2791,16 +2791,16 @@ static void fix_read_error(struct r10conf *conf, struct mddev *mddev, struct r10
 			 * as bad on the first device to discourage future
 			 * reads.
 			 */
-			int dn = r10_bio->devs[r10_bio->read_slot].devnum;
+			int dn = r10_bio->devs[slot].devnum;
 			rdev = conf->mirrors[dn].rdev;
 
 			if (!rdev_set_badblocks(
 				    rdev,
-				    r10_bio->devs[r10_bio->read_slot].addr
+				    r10_bio->devs[slot].addr
 				    + sect,
 				    s, 0)) {
 				md_error(mddev, rdev);
-				r10_bio->devs[r10_bio->read_slot].bio
+				r10_bio->devs[slot].bio
 					= IO_BLOCKED;
 			}
 			break;
@@ -2809,7 +2809,7 @@ static void fix_read_error(struct r10conf *conf, struct mddev *mddev, struct r10
 		start = sl;
 		/* write it back and re-read */
 		rcu_read_lock();
-		while (sl != r10_bio->read_slot) {
+		while (sl != slot) {
 			if (sl==0)
 				sl = conf->copies;
 			sl--;
@@ -2843,7 +2843,7 @@ static void fix_read_error(struct r10conf *conf, struct mddev *mddev, struct r10
 			rcu_read_lock();
 		}
 		sl = start;
-		while (sl != r10_bio->read_slot) {
+		while (sl != slot) {
 			if (sl==0)
 				sl = conf->copies;
 			sl--;