linux-kernel - [092/107] 6pack,mkiss: fix lock inconsistency

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Date:	Thu, 07 Jul 2011 17:17:04 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Arnd Bergmann <arnd@...db.de>,
	Ralf Baechle <ralf@...ux-mips.org>,
	"David S. Miller" <davem@...emloft.net>
Subject: [092/107] 6pack,mkiss: fix lock inconsistency

2.6.39-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Arnd Bergmann <arnd@...db.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@...e.fr>
Tested-by: Bernard F6BVP <f6bvp@...e.fr>
Signed-off-by: Arnd Bergmann <arnd@...db.de>
Acked-by: Ralf Baechle<ralf@...ux-mips.org>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.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
@@ -692,10 +692,10 @@ 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
@@ -813,10 +813,10 @@ 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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