Some error paths in mtd_blkdevs were fixed in the following commit:
commit 94735ec404
mtd: mtd_blkdevs: fix error path in blktrans_open
But on these error paths, the block device's `dev->open' count is
already incremented before we check for errors. This meant that, while
the error path was handled correctly on the first time through
blktrans_open(), the device is erroneously considered already open on
the second time through.
This problem can be seen, for instance, when a UBI volume is
simultaneously mounted as a UBIFS partition and read through its
corresponding gluebi mtdblockX device. This results in blktrans_open()
passing its error checks (with `dev->open > 0') without actually having
a handle on the device. Here's a summarized log of the actions and
results with nandsim:
# modprobe nandsim
# modprobe mtdblock
# modprobe gluebi
# modprobe ubifs
# ubiattach /dev/ubi_ctrl -m 0
...
# ubimkvol /dev/ubi0 -N test -s 16MiB
...
# mount -t ubifs ubi0:test /mnt
# ls /dev/mtdblock*
/dev/mtdblock0 /dev/mtdblock1
# cat /dev/mtdblock1 > /dev/null
cat: can't open '/dev/mtdblock4': Device or resource busy
# cat /dev/mtdblock1 > /dev/null
CPU 0 Unable to handle kernel paging request at virtual address
fffffff0, epc == 8031536c, ra == 8031f280
Oops[#1]:
...
Call Trace:
[<8031536c>] ubi_leb_read+0x14/0x164
[<8031f280>] gluebi_read+0xf0/0x148
[<802edba8>] mtdblock_readsect+0x64/0x198
[<802ecfe4>] mtd_blktrans_thread+0x330/0x3f4
[<8005be98>] kthread+0x88/0x90
[<8000bc04>] kernel_thread_helper+0x10/0x18
Cc: stable@kernel.org [3.0+]
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
342ff28f5a