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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@gmail.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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