[PATCH] md: zero the original position of sb for 0.90 and 1.0

[Jianchao Wang <jianchao.w.wang@xxxxxxxxxx>]

For sb version 0.90 and 1.0 which locates after data, when we increase
the spindle volume size and grow the raid arry size, the older sb which is
different between spindles will be left there. Due to this left sb, the
spindle volume cannot be grown with zero filled part with  --asume-clean.
applications have to take some workarounds such as sync_min/max to avoid
resync.

It is easy and convevient for md to zero the older sb position after
write sb to new position, so do it here.

Cc: robert.butera@xxxxxxxxxx
Signed-off-by: Jianchao Wang <jianchao.w.wang@xxxxxxxxxx>
---
 drivers/md/md.c | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index c208c01..a042add 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -1020,6 +1020,23 @@ int md_check_no_bitmap(struct mddev *mddev)
 }
 EXPORT_SYMBOL(md_check_no_bitmap);
 
+static void md_zero_original_sb_position(struct md_rdev *rdev, sector_t old_pos)
+{
+	struct page *zero_pg;
+
+	zero_pg = alloc_pages(GFP_KERNEL | __GFP_ZERO, 0);
+	if (!zero_pg) {
+		pr_warn("%s: failed to get page for zero original sb position",
+				mdname(rdev->mddev));
+		return;
+	}
+	md_super_write(rdev->mddev, rdev, old_pos, rdev->sb_size,
+		       zero_pg);
+	wait_event(rdev->mddev->sb_wait,
+			(atomic_read(&rdev->mddev->pending_writes) == 0));
+	__free_pages(zero_pg, 0);
+}
+
 /*
  * load_super for 0.90.0
  */
@@ -1394,6 +1411,8 @@ static void super_90_sync(struct mddev *mddev, struct md_rdev *rdev)
 static unsigned long long
 super_90_rdev_size_change(struct md_rdev *rdev, sector_t num_sectors)
 {
+	sector_t old_pos = rdev->sb_start;
+
 	if (num_sectors && num_sectors < rdev->mddev->dev_sectors)
 		return 0; /* component must fit device */
 	if (rdev->mddev->bitmap_info.offset)
@@ -1411,6 +1430,8 @@ super_90_rdev_size_change(struct md_rdev *rdev, sector_t num_sectors)
 		md_super_write(rdev->mddev, rdev, rdev->sb_start, rdev->sb_size,
 		       rdev->sb_page);
 	} while (md_super_wait(rdev->mddev) < 0);
+
+	md_zero_original_sb_position(rdev, old_pos);
 	return num_sectors;
 }
 
@@ -1953,6 +1974,8 @@ super_1_rdev_size_change(struct md_rdev *rdev, sector_t num_sectors)
 {
 	struct mdp_superblock_1 *sb;
 	sector_t max_sectors;
+	sector_t old_pos = 0;
+
 	if (num_sectors && num_sectors < rdev->mddev->dev_sectors)
 		return 0; /* component must fit device */
 	if (rdev->data_offset != rdev->new_data_offset)
@@ -1969,6 +1992,7 @@ super_1_rdev_size_change(struct md_rdev *rdev, sector_t num_sectors)
 	} else {
 		/* minor version 0; superblock after data */
 		sector_t sb_start;
+		old_pos = rdev->sb_start;
 		sb_start = (i_size_read(rdev->bdev->bd_inode) >> 9) - 8*2;
 		sb_start &= ~(sector_t)(4*2 - 1);
 		max_sectors = rdev->sectors + sb_start - rdev->sb_start;
@@ -1984,6 +2008,9 @@ super_1_rdev_size_change(struct md_rdev *rdev, sector_t num_sectors)
 		md_super_write(rdev->mddev, rdev, rdev->sb_start, rdev->sb_size,
 			       rdev->sb_page);
 	} while (md_super_wait(rdev->mddev) < 0);
+
+	if (old_pos)
+		md_zero_original_sb_position(rdev, old_pos);
 	return num_sectors;
 
 }
-- 
2.7.4

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