block: don't take lock on changing ra_pages

There's no need to take queue_lock or kernel_lock when modifying
bdi->ra_pages. So remove them. Also remove out of date comment for
queue_max_sectors_store().
Signed-off-by: Wu Fengguang <wfg@linux.intel.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

block/blk-sysfs.c

@@ -88,9 +88,7 @@ queue_ra_store(struct request_queue *q, const char *page, size_t count)
 	unsigned long ra_kb;
 	ssize_t ret = queue_var_store(&ra_kb, page, count);
 
-	spin_lock_irq(q->queue_lock);
 	q->backing_dev_info.ra_pages = ra_kb >> (PAGE_CACHE_SHIFT - 10);
-	spin_unlock_irq(q->queue_lock);
 
 	return ret;
 }
@@ -117,10 +115,7 @@ queue_max_sectors_store(struct request_queue *q, const char *page, size_t count)
 
 	if (max_sectors_kb > max_hw_sectors_kb || max_sectors_kb < page_kb)
 		return -EINVAL;
-	/*
-	 * Take the queue lock to update the readahead and max_sectors
-	 * values synchronously:
-	 */
+
 	spin_lock_irq(q->queue_lock);
 	q->max_sectors = max_sectors_kb << 1;
 	spin_unlock_irq(q->queue_lock);

block/compat_ioctl.c

@@ -774,9 +774,7 @@ long compat_blkdev_ioctl(struct file *file, unsigned cmd, unsigned long arg)
 		bdi = blk_get_backing_dev_info(bdev);
 		if (bdi == NULL)
 			return -ENOTTY;
-		lock_kernel();
 		bdi->ra_pages = (arg * 512) / PAGE_CACHE_SIZE;
-		unlock_kernel();
 		return 0;
 	case BLKGETSIZE:
 		size = bdev->bd_inode->i_size;

block/ioctl.c

@@ -323,9 +323,7 @@ int blkdev_ioctl(struct block_device *bdev, fmode_t mode, unsigned cmd,
 		bdi = blk_get_backing_dev_info(bdev);
 		if (bdi == NULL)
 			return -ENOTTY;
-		lock_kernel();
 		bdi->ra_pages = (arg * 512) / PAGE_CACHE_SIZE;
-		unlock_kernel();
 		return 0;
 	case BLKBSZSET:
 		/* set the logical block size */