首先执行命令：
tail -f /var/log/syslog
然后插入有问题的U盘，tail会打印一些log：

Dec  6 17:31:53 raj-XPS-8930 kernel: [31581.102997] sd 8:0:0:0: [sde] Write Protect is off
Dec  6 17:31:53 raj-XPS-8930 kernel: [31581.103001] sd 8:0:0:0: [sde] Mode Sense: 23 00 00 00
Dec  6 17:31:53 raj-XPS-8930 kernel: [31581.103598] sd 8:0:0:0: [sde] No Caching mode page found
Dec  6 17:31:53 raj-XPS-8930 kernel: [31581.103603] sd 8:0:0:0: [sde] Assuming drive cache: write through
Dec  6 17:31:53 raj-XPS-8930 kernel: [31581.109415]  sde: sde1
Dec  6 17:31:53 raj-XPS-8930 kernel: [31581.112218] sd 8:0:0:0: [sde] Attached SCSI removable disk
Dec  6 17:31:54 raj-XPS-8930 kernel: [31581.395372] FAT-fs (sde1): Volume was not properly unmounted. Some data may be corrupt. Please run fsck.
Dec  6 17:31:54 raj-XPS-8930 systemd[1]: Started Clean the /media/raj/UBUNTU 18_0 mount point.
Dec  6 17:31:54 raj-XPS-8930 udisksd[1274]: Mounted /dev/sde1 at /media/raj/UBUNTU 18_0 on behalf of uid 1000

最后标明了u盘的名字，出现了一些挂在错误

umount /media/（U盘被挂在后的名字）
sudo dosfsck -v -a /dev/sde1

修复后，u盘能正常读写。