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Subject[19/35] 6pack,mkiss: fix lock inconsistency
2.6.33-longterm review patch.  If anyone has any objections, please let us know.

------------------
From: Arnd Bergmann <arnd@arndb.de>

commit 6e4e2f811bade330126d4029c88c831784a7efd9 upstream.

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>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
drivers/net/hamradio/6pack.c | 4 ++--
drivers/net/hamradio/mkiss.c | 4 ++--
2 files changed, 4 insertions(+), 4 deletions(-)
--- a/drivers/net/hamradio/6pack.c
+++ b/drivers/net/hamradio/6pack.c
@@ -691,10 +691,10 @@ static void sixpack_close(struct tty_str
{
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;

--- a/drivers/net/hamradio/mkiss.c
+++ b/drivers/net/hamradio/mkiss.c
@@ -812,10 +812,10 @@ static void mkiss_close(struct tty_struc
{
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;



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