[U-Boot] UBIFS mount bug when mounting from multiple MTD partitions

[Schrempf Frieder]

Hi,

I have a customer who has a NAND device with two MTD partitions and each 
of the partitions contains one UBI volume with a UBIFS filesystem.

Now U-Boot can mount the UBIFS from the first partition just fine, but 
if the UBIFS from the second partition is mounted afterwards this fails 
in some cases.

I can reproduce the error and tracked it down to uboot_ubifs_mount() in 
fs/ubifs/super.c. If this function is run for the second mount, the 
struct ubifs_fs_type is reused and it contains a list fs_supers, that 
still holds one entry for the first mount.

I guess, that if the second mount would happen on a volume that is on 
the same MTD partition as the first volume, than this will work. The 
second entry is added to ubifs_fs_type.fs_supers.

In my case however, the second entry being added to 
ubifs_fs_type.fs_supers is invalid and causes the mount error.

Reinitializing the list in uboot_ubifs_mount() before each mount, solves 
the problem, but I guess that it will cause failures in other setups, 
where there are actually multiple volumes on one MTD device.

So how can I solve this properly? Do we need one instance of struct 
ubifs_fs_type for each MTD device?

I tested this on an old version (2017.03), but looking at the current 
code, it looks like the same problem applies to current mainline.

Thanks for any help and suggestions!
Frieder