buffer: calculate block number inside folio_init_buffers()

The calculation of block from index doesn't work for devices with a block
size larger than PAGE_SIZE as we end up shifting by a negative number. 
Instead, calculate the number of the first block from the folio's position
in the block device.  We no longer need to pass sizebits to
grow_dev_folio().

Link: https://lkml.kernel.org/r/20231109210608.2252323-3-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Pankaj Raghav <p.raghav@samsung.com>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Cc: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/buffer.c

@@ -995,11 +995,12 @@ static sector_t blkdev_max_block(struct block_device *bdev, unsigned int size)
  * Initialise the state of a blockdev folio's buffers.
  */ 
 static sector_t folio_init_buffers(struct folio *folio,
-		struct block_device *bdev, sector_t block, int size)
+		struct block_device *bdev, unsigned size)
 {
 	struct buffer_head *head = folio_buffers(folio);
 	struct buffer_head *bh = head;
 	bool uptodate = folio_test_uptodate(folio);
+	sector_t block = div_u64(folio_pos(folio), size);
 	sector_t end_block = blkdev_max_block(bdev, size);
 
 	do {
@@ -1032,7 +1033,7 @@ static sector_t folio_init_buffers(struct folio *folio,
  * we succeeded, or the caller should retry.
  */
 static bool grow_dev_folio(struct block_device *bdev, sector_t block,
-		pgoff_t index, unsigned size, int sizebits, gfp_t gfp)
+		pgoff_t index, unsigned size, gfp_t gfp)
 {
 	struct inode *inode = bdev->bd_inode;
 	struct folio *folio;
@@ -1047,8 +1048,7 @@ static bool grow_dev_folio(struct block_device *bdev, sector_t block,
 	bh = folio_buffers(folio);
 	if (bh) {
 		if (bh->b_size == size) {
-			end_block = folio_init_buffers(folio, bdev,
-					(sector_t)index << sizebits, size);
+			end_block = folio_init_buffers(folio, bdev, size);
 			goto unlock;
 		}
 
@@ -1069,8 +1069,7 @@ static bool grow_dev_folio(struct block_device *bdev, sector_t block,
 	 */
 	spin_lock(&inode->i_mapping->private_lock);
 	link_dev_buffers(folio, bh);
-	end_block = folio_init_buffers(folio, bdev,
-			(sector_t)index << sizebits, size);
+	end_block = folio_init_buffers(folio, bdev, size);
 	spin_unlock(&inode->i_mapping->private_lock);
 unlock:
 	folio_unlock(folio);
@@ -1105,7 +1104,7 @@ static bool grow_buffers(struct block_device *bdev, sector_t block,
 	}
 
 	/* Create a folio with the proper size buffers */
-	return grow_dev_folio(bdev, block, index, size, sizebits, gfp);
+	return grow_dev_folio(bdev, block, index, size, gfp);
 }
 
 static struct buffer_head *