[PATCH 3/3] md: pad writes to end of bitmap to physical blocks

[Christopher Unkel]

Writes of the last page of the bitmap are padded out to the next logical
block boundary.  However, they are not padded out to the next physical
block boundary, so the writes may be less than a physical block.  On a
"512e" disk (logical block 512 bytes, physical block 4k) and if the last
page of the bitmap is less than 3584 bytes, this means that writes of
the last bitmap page hit the 512-byte emulation.

Respect the physical block boundary as long as the resulting write
doesn't run into other data, and is no longer than a page.  (If the
physical block size is larger than a page no bitmap write will respect
the physical block boundaries.)

Signed-off-by: Christopher Unkel <cunkel@xxxxxxxxxxxxxx>
---
 drivers/md/md-bitmap.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/md/md-bitmap.c b/drivers/md/md-bitmap.c
index 600b89d5a3ad..21af5f94d495 100644
--- a/drivers/md/md-bitmap.c
+++ b/drivers/md/md-bitmap.c
@@ -264,10 +264,18 @@ static int write_sb_page(struct bitmap *bitmap, struct page *page, int wait)
 
 		if (page->index == store->file_pages-1) {
 			int last_page_size = store->bytes & (PAGE_SIZE-1);
+			int pb_aligned_size;
 			if (last_page_size == 0)
 				last_page_size = PAGE_SIZE;
 			size = roundup(last_page_size,
 				       bdev_logical_block_size(bdev));
+			pb_aligned_size = roundup(last_page_size,
+						  bdev_physical_block_size(bdev));
+			if (pb_aligned_size > size
+			    && pb_aligned_size <= PAGE_SIZE
+			    && sb_write_alignment_ok(mddev, rdev, page, offset,
+						     pb_aligned_size))
+				size = pb_aligned_size;
 		}
 		/* Just make sure we aren't corrupting data or
 		 * metadata
-- 
2.17.1