From: Arnd Bergmann <arnd@arndb.de>
Date: Fri, 1 Jul 2011 23:28:46 +0200

Lockdep found a locking inconsistency in the mkiss_close function:

quoted

kernel: [ INFO: inconsistent lock state ]
kernel: 2.6.39.1 #3
kernel: ---------------------------------
kernel: inconsistent {IN-SOFTIRQ-R} -> {SOFTIRQ-ON-W} usage.
kernel: ax25ipd/2813 [HC0[0]:SC0[0]:HE1:SE1] takes:
kernel: (disc_data_lock){+++?.-}, at: [<ffffffffa018552b>] mkiss_close+0x1b/0x90 [mkiss]
kernel: {IN-SOFTIRQ-R} state was registered at:

The message hints that disc_data_lock is aquired with softirqs disabled,
but does not itself disable softirqs, which can in rare circumstances
lead to a deadlock. 
The same problem is present in the 6pack driver, this patch fixes both
by using write_lock_bh instead of write_lock.

Reported-by: Bernard F6BVP <redacted>
Tested-by: Bernard F6BVP <redacted>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Ralf Baechle<redacted>
Cc: stable@kernel.org

Applied, thanks!