netdev - [PATCH][AX25] af_ax25: remove sock lock in ax25_info

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Message-ID: <20080209235029.GC2754@ami.dom.local>
Date:	Sun, 10 Feb 2008 00:50:29 +0100
From:	Jarek Poplawski <jarkao2@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	Bernard Pidoux F6BVP <f6bvp@...e.fr>,
	Ralf Baechle DL5RB <ralf@...ux-mips.org>,
	Jann Traschewski <jann@....de>, netdev@...r.kernel.org
Subject: [PATCH][AX25] af_ax25: remove sock lock in ax25_info_show()

On Sat, Feb 09, 2008 at 07:44:50PM +0100, Bernard Pidoux F6BVP wrote:
> Hi,
>
> With AX25 patches applied I still get this possible circular locking  
> message.

IMHO this warning could happen earlier too...

Thanks,
Jarek P.

-------------->

Subject: [AX25] af_ax25: remove sock lock in ax25_info_show()
 
This lockdep warning:

> =======================================================
> [ INFO: possible circular locking dependency detected ]
> 2.6.24 #3
> -------------------------------------------------------
> swapper/0 is trying to acquire lock:
>  (ax25_list_lock){-+..}, at: [<f91dd3b1>] ax25_destroy_socket+0x171/0x1f0 [ax25]
> 
> but task is already holding lock:
>  (slock-AF_AX25){-+..}, at: [<f91dbabc>] ax25_std_heartbeat_expiry+0x1c/0xe0 [ax25]
> 
> which lock already depends on the new lock.
...

shows that ax25_list_lock and slock-AF_AX25 are taken in different
order: ax25_info_show() takes slock (bh_lock_sock(ax25->sk)) while
ax25_list_lock is held, so reversely to other functions. To fix this
the sock lock should be moved to ax25_info_start(), but since it's
only for reading proc info it seems this is not necessary (e.g.
ax25_send_to_raw() does similar reading without this lock too). So,
this patch removes this lock to avoid deadlock possibility.


Reported-by: Bernard Pidoux F6BVP <f6bvp@...e.fr>
Signed-off-by: Jarek Poplawski <jarkao2@...il.com>

---

 net/ax25/af_ax25.c |    2 --
 1 files changed, 0 insertions(+), 2 deletions(-)

diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c
index 94b2b1b..68b5171 100644
--- a/net/ax25/af_ax25.c
+++ b/net/ax25/af_ax25.c
@@ -1924,12 +1924,10 @@ static int ax25_info_show(struct seq_file *seq, void *v)
 		   ax25->paclen);
 
 	if (ax25->sk != NULL) {
-		bh_lock_sock(ax25->sk);
 		seq_printf(seq," %d %d %ld\n",
 			   atomic_read(&ax25->sk->sk_wmem_alloc),
 			   atomic_read(&ax25->sk->sk_rmem_alloc),
 			   ax25->sk->sk_socket != NULL ? SOCK_INODE(ax25->sk->sk_socket)->i_ino : 0L);
-		bh_unlock_sock(ax25->sk);
 	} else {
 		seq_puts(seq, " * * *\n");
 	}
--
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