block: read i_size with i_size_read()

Convert direct reads of an inode's i_size to using i_size_read().

i_size_{read,write} use a seqcount to protect reads from accessing
incomple writes.  Concurrent i_size_write()s require mutual exclussion
to protect the seqcount that is used by i_size_{read,write}.  But
i_size_read() callers do not need to use additional locking.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Acked-by: NeilBrown <neilb@suse.de>
Acked-by: Lars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
diff --git a/block/ioctl.c b/block/ioctl.c
index d724ceb..38aa194 100644
--- a/block/ioctl.c
+++ b/block/ioctl.c
@@ -125,7 +125,7 @@
 	start >>= 9;
 	len >>= 9;
 
-	if (start + len > (bdev->bd_inode->i_size >> 9))
+	if (start + len > (i_size_read(bdev->bd_inode) >> 9))
 		return -EINVAL;
 	if (secure)
 		flags |= BLKDEV_DISCARD_SECURE;
@@ -307,12 +307,12 @@
 		ret = blkdev_reread_part(bdev);
 		break;
 	case BLKGETSIZE:
-		size = bdev->bd_inode->i_size;
+		size = i_size_read(bdev->bd_inode);
 		if ((size >> 9) > ~0UL)
 			return -EFBIG;
 		return put_ulong(arg, size >> 9);
 	case BLKGETSIZE64:
-		return put_u64(arg, bdev->bd_inode->i_size);
+		return put_u64(arg, i_size_read(bdev->bd_inode));
 	case BLKTRACESTART:
 	case BLKTRACESTOP:
 	case BLKTRACESETUP: