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Message-ID: <6E42A1B4DD2F7B4D80A1F26BB498BF9F8C9F8C1539@irsmsx501.ger.corp.intel.com>
Date:	Mon, 14 Mar 2011 14:56:20 +0000
From:	"Ferraton, Jean RegisX" <jean.regisx.ferraton@...el.com>
To:	"Gustavo F. Padovan" <padovan@...fusion.mobi>
CC:	"marcel@...tmann.org" <marcel@...tmann.org>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"eric.dumazet@...il.com" <eric.dumazet@...il.com>,
	"xiaosuo@...il.com" <xiaosuo@...il.com>,
	"linux-bluetooth@...r.kernel.org" <linux-bluetooth@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: [PATCH] Fix "possible circular locking dependency" in rfcomm

No response from original post, submit again, more details below:

Changes in sock.c in function __rfcomm_sock_close, to release sock before calling rfcomm_dlc_close to avoid possible deadlock when calling rfcomm_lock (in rfcomm_dlc_close).

Signed-off-by: Jean Regis Ferraton <jrferraton@...il.com>

---
 net/bluetooth/rfcomm/sock.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/net/bluetooth/rfcomm/sock.c b/net/bluetooth/rfcomm/sock.c index 66cc1f0..3b5ec09 100644
--- a/net/bluetooth/rfcomm/sock.c
+++ b/net/bluetooth/rfcomm/sock.c
@@ -234,7 +234,10 @@ static void __rfcomm_sock_close(struct sock *sk)
 	case BT_CONNECT2:
 	case BT_CONFIG:
 	case BT_CONNECTED:
+		/* release_sock to avoid deadlock when calling rfcomm_lock() */
+		release_sock(sk);
 		rfcomm_dlc_close(d, 0);
+		lock_sock(sk);
 
 	default:
 		sock_set_flag(sk, SOCK_ZAPPED);
--
1.6.2.5



This patch solves a problem of "possible circular locking dependency" related to rfcomm. Problem seen on kernel 2.6.37. Maybe it's not a bug, just a warning, see the trace below.

This problem occurs in 2 cases:
1- When initiating a connection from the remote device
2- When browsing my BT device from my PC

My analysis is the following:
1- We call the function rfcomm_sock_shutdown() which locks a socket, an after calls __rfcomm_sock_close()
     	lock_sock(sk);
    	if (!sk->sk_shutdown) {
    		sk->sk_shutdown = SHUTDOWN_MASK;
    		__rfcomm_sock_close(sk);
2- In the function __rfcomm_sock_close(), we call rfcomm_dlc_close()
	case BT_CONNECTED:
    		rfcomm_dlc_close(d, 0);
3- In the function rfcomm_dlc_close(), we call rfcomm_lock() which locks a mutex on rfcomm, and this second lock causes the problem.
	rfcomm_lock();
	r = __rfcomm_dlc_close(d, err);

My message trace is the following (for remote connect):
[  113.995511] =======================================================
[  114.001897] [ INFO: possible circular locking dependency detected ] 
[  114.008157] 2.6.37.3jrf_fix #1 
[  114.011196] -------------------------------------------------------
[  114.017457] bluetoothd/511 is trying to acquire lock:
[  114.022499]  (rfcomm_mutex){+.+.+.}, at: [<c14f281a>] rfcomm_dlc_close+0x15/0x30 
[  114.029887] 
[  114.029892] but task is already holding lock:
[  114.035713]  (sk_lock-AF_BLUETOOTH){+.+.+.}, at: [<c14f4cfe>] rfcomm_sock_shutdown+0x17/0x5d 
[  114.044147] 
[  114.044152] which lock already depends on the new lock.
[  114.044158]
[  114.052319]
[  114.052324] the existing dependency chain (in reverse order) is:
[  114.059796]
[  114.059801] -> #1 (sk_lock-AF_BLUETOOTH){+.+.+.}:
[  114.065967]        [<c105d660>] lock_acquire+0xf9/0x135
[  114.071184]        [<c1445cf3>] lock_sock_nested+0x55/0x65
[  114.076662]        [<c14ed17d>] l2cap_sock_sendmsg+0x3f/0x606
[  114.082400]        [<c1443775>] sock_sendmsg+0xc9/0xe0
[  114.087530]        [<c14437b4>] kernel_sendmsg+0x28/0x37
[  114.092833]        [<c14f2278>] rfcomm_send_frame+0x2f/0x37
[  114.098398]        [<c14f232c>] rfcomm_send_ua+0x57/0x59
[  114.103701]        [<c14f3884>] rfcomm_run+0x431/0xb06
[  114.108830]        [<c104bc8f>] kthread+0x5f/0x64
[  114.113525]        [<c1002b7a>] kernel_thread_helper+0x6/0x1a
[  114.119265]
[  114.119270] -> #0 (rfcomm_mutex){+.+.+.}:
[  114.124739]        [<c105cff1>] __lock_acquire+0xe03/0x1379
[  114.130304]        [<c105d660>] lock_acquire+0xf9/0x135
[  114.135522]        [<c1522bf3>] mutex_lock_nested+0x45/0x286
[  114.141171]        [<c14f281a>] rfcomm_dlc_close+0x15/0x30
[  114.146650]        [<c14f4cdb>] __rfcomm_sock_close+0x5e/0x6a
[  114.152388]        [<c14f4d12>] rfcomm_sock_shutdown+0x2b/0x5d
[  114.158212]        [<c14f4d5d>] rfcomm_sock_release+0x19/0x60
[  114.163951]        [<c14445da>] sock_release+0x14/0x5b
[  114.169080]        [<c144463d>] sock_close+0x1c/0x20
[  114.174037]        [<c10bdd19>] fput+0xfa/0x19e
[  114.178557]        [<c10bb3c5>] filp_close+0x51/0x5b
[  114.183512]        [<c10bb488>] sys_close+0xb9/0xee
[  114.188381]        [<c1002650>] sysenter_do_call+0x12/0x36
[  114.193858]
[  114.193863] other info that might help us debug this:
[  114.193870]
[  114.201860] 1 lock held by bluetoothd/511:
[  114.205945]  #0:  (sk_lock-AF_BLUETOOTH){+.+.+.}, at: [<c14f4cfe>] rfcomm_sock_shutdown+0x17/0x5d
[  114.214811]
[  114.214816] stack backtrace:
[  114.219167] Pid: 511, comm: bluetoothd Tainted: G        WC  2.6.37.3jrf_fix #1
[  114.226463] Call Trace:
[  114.228913]  [<c152108a>] ? printk+0xf/0x11 
[  114.233086]  [<c105bc3b>] print_circular_bug+0x90/0x9c 
[  114.238211]  [<c105cff1>] __lock_acquire+0xe03/0x1379 
[  114.243260]  [<c14f281a>] ? rfcomm_dlc_close+0x15/0x30 
[  114.248382]  [<c105d660>] lock_acquire+0xf9/0x135 
[  114.253079]  [<c14f281a>] ? rfcomm_dlc_close+0x15/0x30 
[  114.258208]  [<c1522bf3>] mutex_lock_nested+0x45/0x286 
[  114.263338]  [<c14f281a>] ? rfcomm_dlc_close+0x15/0x30 
[  114.268469]  [<c105b68d>] ? trace_hardirqs_on_caller+0x100/0x121
[  114.274467]  [<c1445cf8>] ? lock_sock_nested+0x5a/0x65 
[  114.279597]  [<c105b6b9>] ? trace_hardirqs_on+0xb/0xd 
[  114.284639]  [<c14f281a>] rfcomm_dlc_close+0x15/0x30 
[  114.289594]  [<c14f4cdb>] __rfcomm_sock_close+0x5e/0x6a 
[  114.294811]  [<c14f4d12>] rfcomm_sock_shutdown+0x2b/0x5d 
[  114.300115]  [<c14f4d5d>] rfcomm_sock_release+0x19/0x60 
[  114.305331]  [<c14445da>] sock_release+0x14/0x5b 
[  114.309937]  [<c144463d>] sock_close+0x1c/0x20 
[  114.314373]  [<c10bdd19>] fput+0xfa/0x19e 
[  114.318371]  [<c10bb3c5>] filp_close+0x51/0x5b 
[  114.322804]  [<c10bb488>] sys_close+0xb9/0xee 
[  114.327151]  [<c1002650>] sysenter_do_call+0x12/0x36
---------------------------------------------------------------------
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Registered headquarters: "Les Montalets"- 2, rue de Paris, 
92196 Meudon Cedex, France
Registration Number:  302 456 199 R.C.S. NANTERRE
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