block: fix wrong mode for blkdev_get_by_dev() from disk_scan_partitions()

After commit 2736e8e ("block: use the holder as indication for
exclusive opens"), blkdev_get_by_dev() will warn if holder is NULL and
mode contains 'FMODE_EXCL'.

holder from blkdev_get_by_dev() from disk_scan_partitions() is always NULL,
hence it should not use 'FMODE_EXCL', which is broben by the commit. For
consequence, WARN_ON_ONCE() will be triggered from blkdev_get_by_dev()
if user scan partitions with device opened exclusively.

Fix this problem by removing 'FMODE_EXCL' from disk_scan_partitions(),
as it used to be.

Reported-by: [email protected]
Link: https://syzkaller.appspot.com/bug?extid=00cd27751f78817f167b
Fixes: 2736e8e ("block: use the holder as indication for exclusive opens")
Signed-off-by: Yu Kuai <[email protected]>
Reviewed-by: Christian Brauner <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

Author: YuKuai-huawei

block/genhd.c

@@ -366,7 +366,8 @@ int disk_scan_partitions(struct gendisk *disk, blk_mode_t mode)
 	}
 
 	set_bit(GD_NEED_PART_SCAN, &disk->state);
-	bdev = blkdev_get_by_dev(disk_devt(disk), mode, NULL, NULL);
+	bdev = blkdev_get_by_dev(disk_devt(disk), mode & ~FMODE_EXEC, NULL,
+				 NULL);
 	if (IS_ERR(bdev))
 		ret =  PTR_ERR(bdev);
 	else