From: Jarek Poplawski <jarkao2@gmail.com>
Date: Tue, 12 Feb 2008 05:24:56 +0000 (-0800)
Subject: [AX25] af_ax25: remove sock lock in ax25_info_show()
X-Git-Tag: v2.6.25-rc2~2^2~27
X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=1105b5d1d44e6f00e31422dfcb0139bc8ae966a9;p=linux-2.6

[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(), and there would
be still problem with breaking ax25_list_lock (it seems this "proper"
order isn't optimal yet). 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 sock lock to avoid deadlock possibility; there
is also used sock_i_ino() function, which reads sk_socket under proper
read lock. Additionally printf format of this i_ino is changed to %lu.

Reported-by: Bernard Pidoux F6BVP <f6bvp@free.fr>
Signed-off-by: Jarek Poplawski <jarkao2@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---

diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c
index 8fc64e3150..5a4337a290 100644
--- a/net/ax25/af_ax25.c
+++ b/net/ax25/af_ax25.c
@@ -1928,12 +1928,10 @@ 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",
+		seq_printf(seq, " %d %d %lu\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);
+			   sock_i_ino(ax25->sk));
 	} else {
 		seq_puts(seq, " * * *\n");
 	}