loop: set physical block size to logical block size

Commit 6c6b6f28b333 ("loop: set physical block size to PAGE_SIZE")
caused mkfs.xfs to barf on ppc64 [1]. Always using PAGE_SIZE as the
physical block size still makes the most sense semantically, but let's
just lie and always set it to the same value as the logical block size
(same goes for io_min). In the future we might want to at least bump up
io_min to PAGE_SIZE but I'm sick of these stupid changes so let's play
it safe.

1: https://marc.info/?l=linux-xfs&m=150459024723753&w=2

Tested-by: Chandan Rajendra <chandan@linux.vnet.ibm.com>
Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/loop.c

@@ -1036,6 +1036,8 @@ static int loop_clr_fd(struct loop_device *lo)
 	memset(lo->lo_crypt_name, 0, LO_NAME_SIZE);
 	memset(lo->lo_file_name, 0, LO_NAME_SIZE);
 	blk_queue_logical_block_size(lo->lo_queue, 512);
+	blk_queue_physical_block_size(lo->lo_queue, 512);
+	blk_queue_io_min(lo->lo_queue, 512);
 	if (bdev) {
 		bdput(bdev);
 		invalidate_bdev(bdev);
@@ -1330,6 +1332,8 @@ static int loop_set_block_size(struct loop_device *lo, unsigned long arg)
 	blk_mq_freeze_queue(lo->lo_queue);
 
 	blk_queue_logical_block_size(lo->lo_queue, arg);
+	blk_queue_physical_block_size(lo->lo_queue, arg);
+	blk_queue_io_min(lo->lo_queue, arg);
 	loop_update_dio(lo);
 
 	blk_mq_unfreeze_queue(lo->lo_queue);
@@ -1777,8 +1781,6 @@ static int loop_add(struct loop_device **l, int i)
 	}
 	lo->lo_queue->queuedata = lo;
 
-	blk_queue_physical_block_size(lo->lo_queue, PAGE_SIZE);
-
 	blk_queue_max_hw_sectors(lo->lo_queue, BLK_DEF_MAX_SECTORS);
 
 	/*