netdev - Re: [AX25] inconsistent lock state

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Message-Id: <201106171536.15660.arnd@arndb.de>
Date:	Fri, 17 Jun 2011 15:36:15 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	f6bvp <f6bvp@...e.fr>
Cc:	linux-kernel@...r.kernel.org, Jarek Poplawski <jarkao2@...il.com>,
	Linux Netdev List <netdev@...r.kernel.org>,
	Ralf Baechle <ralf@...ux-mips.org>, linux-hams@...r.kernel.org
Subject: Re: [AX25] inconsistent lock state

On Thursday 16 June 2011 22:23:09 f6bvp wrote:

> Jun 16 12:03:34 f6bvp-9 kernel: =================================
> Jun 16 12:03:34 f6bvp-9 kernel: [ INFO: inconsistent lock state ]
> Jun 16 12:03:34 f6bvp-9 kernel: 2.6.39.1 #3
> Jun 16 12:03:34 f6bvp-9 kernel: ---------------------------------
> Jun 16 12:03:34 f6bvp-9 kernel: inconsistent {IN-SOFTIRQ-R} -> {SOFTIRQ-ON-W} usage.
> Jun 16 12:03:34 f6bvp-9 kernel: ax25ipd/2813 [HC0[0]:SC0[0]:HE1:SE1] takes:
> Jun 16 12:03:34 f6bvp-9 kernel: (disc_data_lock){+++?.-}, at: [<ffffffffa018552b>] mkiss_close+0x1b/0x90 [mkiss]
> Jun 16 12:03:34 f6bvp-9 kernel: {IN-SOFTIRQ-R} state was registered at:
> ...
> Is there something wrong in AX25 code or (more unlikely) is this 
> operation not permitted ?

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.

Does this fix it?

Signed-off-by: Arnd Bergmann <arnd@...db.de>

--- a/drivers/net/hamradio/mkiss.c
+++ b/drivers/net/hamradio/mkiss.c
@@ -708,11 +708,11 @@ static struct mkiss *mkiss_get(struct tty_struct *tty)
 {
 	struct mkiss *ax;
 
-	read_lock(&disc_data_lock);
+	read_lock_bh(&disc_data_lock);
 	ax = tty->disc_data;
 	if (ax)
 		atomic_inc(&ax->refcnt);
-	read_unlock(&disc_data_lock);
+	read_unlock_bh(&disc_data_lock);
 
 	return ax;
 }
@@ -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;
--
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