Unable to remount ubifs after many unclean reboot

[Olivier Singla]

Hi,

I am working for an embedded system using 4GB NAND Flash
(MT29F32G08ABAAAWP), ubifs, and 3.6.5 kernel (A9 dualcore).. Using a
simple test program, I am able to have UBIFS to fail to mount the NAND
partition (I am using pretty much all the 4GB of the NAND). The test
is quite simple: mount the ubifs partition at boot time, then write a
file (justa  few KB), do a sync, wait a few seconds, and then reboot
(/sbin/reboot, and -important point- I have a micro-controller which
does a power-cycle). Intentionally, I did NOT unmount the ubifs
partition. Later on, I changed the test to unmount the ubifs partition
(but I still do not detach the ubi volume). What I am seeing is that
after many iterations (usually around a thousand), ubifs could not
mount the ubifs partition, both under u-boot and Linux.

Under Linux, this is what I see when ubifs try to mount the partition:

[   55.646884] UBIFS: background thread "ubifs_bgt0_0" started, PID 858
[   56.013037] UBIFS: recovery needed
[   56.258731] UBI warning: ubi_io_read: error -119 while reading
294912 bytes from PEB 600:753664, read only 294912 bytes, retry
[   56.320616] UBI warning: ubi_io_read: error -119 while reading
294912 bytes from PEB 600:753664, read only 294912 bytes, retry
[   56.382444] UBI warning: ubi_io_read: error -119 while reading
294912 bytes from PEB 600:753664, read only 294912 bytes, retry
[   56.444263] UBI error: ubi_io_read: error -119 while reading 294912
bytes from PEB 600:753664, read 294912 bytes
[   56.454775] CPU: 0 PID: 857 Comm: mount Not tainted 3.14.29 #16
[   56.460888] Backtrace:
[   56.463441] [<c0011ea8>] (dump_backtrace) from [<c00120bc>]
(show_stack+0x18/0x1c)
[   56.471255]  r7:000b8000 r6:ede50000 r5:00000000 r4:c06c730c
[   56.477151] [<c00120a4>] (show_stack) from [<c04f4074>]
(dump_stack+0x94/0xcc)
[   56.484636] [<c04f3fe0>] (dump_stack) from [<c031d390>]
(ubi_io_read+0x134/0x314)
[   56.492356]  r7:000b8000 r6:00000000 r5:00048000 r4:ffffff89
[   56.498233] [<c031d25c>] (ubi_io_read) from [<c031ae84>]
(ubi_eba_read_leb+0x140/0x3e4)
etc.

At this point, my only option is to erase the NAND, and recreate the
UBIFS partition, which I can then use as usual. When I redo the test,
the PEB failing are at a different address in the flash, but this is
still a whole nand erase block size (1 MB in the case of this nand
part).

I realize this test might not be realistic, but the idea is to test
how the system would behave after several power loss, with and without
clean unmount.

I noticed that even after un-mounting the ubifs partition the ubi
working thread (ubifs_bgt0_0) is still running. I am wondering if this
thread could schedule a nand erase even in the case of the ubisfs
partition unmounted? If this is the case, doing the ubidetach, which
stop the thread should help, is that a fair statement?

I thought that the whole idea of ubifs was to be protected again
unexpected loss of power. I understand that obviously I could loose
some data, but at least ubifs should be able to mount the partition.

Any idea what could be wrong? And also should using ubidetach help, in
the case of testing reboot with clean unmount ?