6pack,mkiss: fix lock inconsistency
Arnd Bergmann [Sat, 2 Jul 2011 00:30:00 +0000 (17:30 -0700)]
Lockdep found a locking inconsistency in the mkiss_close function:

> 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 <f6bvp@free.fr>
Tested-by: Bernard F6BVP <f6bvp@free.fr>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Ralf Baechle<ralf@linux-mips.org>
Cc: stable@kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/hamradio/6pack.c
drivers/net/hamradio/mkiss.c

index 3e5d0b6..0d28378 100644 (file)
@@ -692,10 +692,10 @@ static void sixpack_close(struct tty_struct *tty)
 {
        struct sixpack *sp;
 
-       write_lock(&disc_data_lock);
+       write_lock_bh(&disc_data_lock);
        sp = tty->disc_data;
        tty->disc_data = NULL;
-       write_unlock(&disc_data_lock);
+       write_unlock_bh(&disc_data_lock);
        if (!sp)
                return;
 
index 4c62839..bc02968 100644 (file)
@@ -813,10 +813,10 @@ static void mkiss_close(struct tty_struct *tty)
 {
        struct mkiss *ax;
 
-       write_lock(&disc_data_lock);
+       write_lock_bh(&disc_data_lock);
        ax = tty->disc_data;
        tty->disc_data = NULL;
-       write_unlock(&disc_data_lock);
+       write_unlock_bh(&disc_data_lock);
 
        if (!ax)
                return;