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2024-02-20 102a0743326a03cd1a1202ceda21e175b7d3575c

 kernel/drivers/md/raid0.c
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@@ -274,6 +274,18 @@
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 		goto abort;
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 	}
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+	if (conf->layout == RAID0_ORIG_LAYOUT) {
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+		for (i = 1; i < conf->nr_strip_zones; i++) {
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+			sector_t first_sector = conf->strip_zone[i-1].zone_end;
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+
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+			sector_div(first_sector, mddev->chunk_sectors);
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+			zone = conf->strip_zone + i;
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+			/* disk_shift is first disk index used in the zone */
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+			zone->disk_shift = sector_div(first_sector,
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+						      zone->nb_dev);
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+		}
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+	}
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+
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 	pr_debug("md/raid0:%s: done.\n", mdname(mddev));
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 	*private_conf = conf;
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..
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@@ -427,6 +439,20 @@
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 	kfree(conf);
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 }
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+/*
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+ * Convert disk_index to the disk order in which it is read/written.
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+ *  For example, if we have 4 disks, they are numbered 0,1,2,3. If we
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+ *  write the disks starting at disk 3, then the read/write order would
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+ *  be disk 3, then 0, then 1, and then disk 2 and we want map_disk_shift()
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+ *  to map the disks as follows 0,1,2,3 => 1,2,3,0. So disk 0 would map
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+ *  to 1, 1 to 2, 2 to 3, and 3 to 0. That way we can compare disks in
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+ *  that 'output' space to understand the read/write disk ordering.
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+ */
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+static int map_disk_shift(int disk_index, int num_disks, int disk_shift)
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+{
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+	return ((disk_index + num_disks - disk_shift) % num_disks);
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+}
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+
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 static void raid0_handle_discard(struct mddev *mddev, struct bio *bio)
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 {
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 	struct r0conf *conf = mddev->private;
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@@ -440,7 +466,9 @@
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 	sector_t end_disk_offset;
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 	unsigned int end_disk_index;
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 	unsigned int disk;
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+	sector_t orig_start, orig_end;
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+	orig_start = start;
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 	zone = find_zone(conf, &start);
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 	if (bio_end_sector(bio) > zone->zone_end) {
..
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@@ -454,6 +482,7 @@
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 	} else
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 		end = bio_end_sector(bio);
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+	orig_end = end;
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 	if (zone != conf->strip_zone)
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 		end = end - zone[-1].zone_end;
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@@ -465,13 +494,26 @@
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 	last_stripe_index = end;
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 	sector_div(last_stripe_index, stripe_size);
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-	start_disk_index = (int)(start - first_stripe_index * stripe_size) /
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-		mddev->chunk_sectors;
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+	/* In the first zone the original and alternate layouts are the same */
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+	if ((conf->layout == RAID0_ORIG_LAYOUT) && (zone != conf->strip_zone)) {
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+		sector_div(orig_start, mddev->chunk_sectors);
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+		start_disk_index = sector_div(orig_start, zone->nb_dev);
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+		start_disk_index = map_disk_shift(start_disk_index,
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+						  zone->nb_dev,
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+						  zone->disk_shift);
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+		sector_div(orig_end, mddev->chunk_sectors);
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+		end_disk_index = sector_div(orig_end, zone->nb_dev);
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+		end_disk_index = map_disk_shift(end_disk_index,
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+						zone->nb_dev, zone->disk_shift);
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+	} else {
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+		start_disk_index = (int)(start - first_stripe_index * stripe_size) /
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+			mddev->chunk_sectors;
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+		end_disk_index = (int)(end - last_stripe_index * stripe_size) /
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+			mddev->chunk_sectors;
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+	}
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 	start_disk_offset = ((int)(start - first_stripe_index * stripe_size) %
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 		mddev->chunk_sectors) +
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 		first_stripe_index * mddev->chunk_sectors;
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-	end_disk_index = (int)(end - last_stripe_index * stripe_size) /
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-		mddev->chunk_sectors;
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 	end_disk_offset = ((int)(end - last_stripe_index * stripe_size) %
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 		mddev->chunk_sectors) +
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 		last_stripe_index * mddev->chunk_sectors;
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@@ -480,18 +522,22 @@
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 		sector_t dev_start, dev_end;
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 		struct bio *discard_bio = NULL;
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 		struct md_rdev *rdev;
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+		int compare_disk;
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-		if (disk < start_disk_index)
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+		compare_disk = map_disk_shift(disk, zone->nb_dev,
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+					      zone->disk_shift);
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+
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+		if (compare_disk < start_disk_index)
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 			dev_start = (first_stripe_index + 1) *
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 				mddev->chunk_sectors;
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-		else if (disk > start_disk_index)
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+		else if (compare_disk > start_disk_index)
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 			dev_start = first_stripe_index * mddev->chunk_sectors;
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 		else
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 			dev_start = start_disk_offset;
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-		if (disk < end_disk_index)
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+		if (compare_disk < end_disk_index)
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 			dev_end = (last_stripe_index + 1) * mddev->chunk_sectors;
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-		else if (disk > end_disk_index)
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+		else if (compare_disk > end_disk_index)
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 			dev_end = last_stripe_index * mddev->chunk_sectors;
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 		else
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 			dev_end = end_disk_offset;