This patch reduces the critical section protected by sco_conn_lock in
sco_conn_ready function. The lock is acquired only when it is really
needed.
This patch fixes the following lockdep warning which is generated
when the host terminates a SCO connection.
Today, this warning is a false positive. There is no way those
two threads reported by lockdep are running at the same time since
hdev->workqueue (where rx_work is queued) is single-thread. However,
if somehow this behavior is changed in future, we will have a
potential deadlock.
======================================================
[ INFO: possible circular locking dependency detected ]
3.8.0-rc1+ #7 Not tainted
-------------------------------------------------------
kworker/u:1H/1018 is trying to acquire lock:
(&(&conn->lock)->rlock){+.+...}, at: [<ffffffffa0033ba6>] sco_chan_del+0x66/0x190 [bluetooth]
but task is already holding lock:
(slock-AF_BLUETOOTH-BTPROTO_SCO){+.+...}, at: [<ffffffffa0033d5a>] sco_conn_del+0x8a/0xe0 [bluetooth]
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (slock-AF_BLUETOOTH-BTPROTO_SCO){+.+...}:
[<ffffffff81083011>] lock_acquire+0xb1/0xe0
[<ffffffff813efd01>] _raw_spin_lock+0x41/0x80
[<ffffffffa003436e>] sco_connect_cfm+0xbe/0x350 [bluetooth]
[<ffffffffa0015d6c>] hci_event_packet+0xd3c/0x29b0 [bluetooth]
[<ffffffffa0004583>] hci_rx_work+0x133/0x870 [bluetooth]
[<ffffffff8104d65f>] process_one_work+0x2bf/0x4f0
[<ffffffff81050022>] worker_thread+0x2b2/0x3e0
[<ffffffff81056021>] kthread+0xd1/0xe0
[<ffffffff813f14bc>] ret_from_fork+0x7c/0xb0
-> #0 (&(&conn->lock)->rlock){+.+...}:
[<ffffffff81082215>] __lock_acquire+0x1465/0x1c70
[<ffffffff81083011>] lock_acquire+0xb1/0xe0
[<ffffffff813efd01>] _raw_spin_lock+0x41/0x80
[<ffffffffa0033ba6>] sco_chan_del+0x66/0x190 [bluetooth]
[<ffffffffa0033d6d>] sco_conn_del+0x9d/0xe0 [bluetooth]
[<ffffffffa0034653>] sco_disconn_cfm+0x53/0x60 [bluetooth]
[<ffffffffa000fef3>] hci_disconn_complete_evt.isra.54+0x363/0x3c0 [bluetooth]
[<ffffffffa00150f7>] hci_event_packet+0xc7/0x29b0 [bluetooth]
[<ffffffffa0004583>] hci_rx_work+0x133/0x870 [bluetooth]
[<ffffffff8104d65f>] process_one_work+0x2bf/0x4f0
[<ffffffff81050022>] worker_thread+0x2b2/0x3e0
[<ffffffff81056021>] kthread+0xd1/0xe0
[<ffffffff813f14bc>] ret_from_fork+0x7c/0xb0
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(slock-AF_BLUETOOTH-BTPROTO_SCO);
lock(&(&conn->lock)->rlock);
lock(slock-AF_BLUETOOTH-BTPROTO_SCO);
lock(&(&conn->lock)->rlock);
*** DEADLOCK ***
4 locks held by kworker/u:1H/1018:
#0: (hdev->name#2){.+.+.+}, at: [<ffffffff8104d5f8>] process_one_work+0x258/0x4f0
#1: ((&hdev->rx_work)){+.+.+.}, at: [<ffffffff8104d5f8>] process_one_work+0x258/0x4f0
#2: (&hdev->lock){+.+.+.}, at: [<ffffffffa000fbe9>] hci_disconn_complete_evt.isra.54+0x59/0x3c0 [bluetooth]
#3: (slock-AF_BLUETOOTH-BTPROTO_SCO){+.+...}, at: [<ffffffffa0033d5a>] sco_conn_del+0x8a/0xe0 [bluetooth]
stack backtrace:
Pid: 1018, comm: kworker/u:1H Not tainted 3.8.0-rc1+ #7
Call Trace:
[<ffffffff813e92f9>] print_circular_bug+0x1fb/0x20c
[<ffffffff81082215>] __lock_acquire+0x1465/0x1c70
[<ffffffff81083011>] lock_acquire+0xb1/0xe0
[<ffffffffa0033ba6>] ? sco_chan_del+0x66/0x190 [bluetooth]
[<ffffffff813efd01>] _raw_spin_lock+0x41/0x80
[<ffffffffa0033ba6>] ? sco_chan_del+0x66/0x190 [bluetooth]
[<ffffffffa0033ba6>] sco_chan_del+0x66/0x190 [bluetooth]
[<ffffffffa0033d6d>] sco_conn_del+0x9d/0xe0 [bluetooth]
[<ffffffffa0034653>] sco_disconn_cfm+0x53/0x60 [bluetooth]
[<ffffffffa000fef3>] hci_disconn_complete_evt.isra.54+0x363/0x3c0 [bluetooth]
[<ffffffffa000fbd0>] ? hci_disconn_complete_evt.isra.54+0x40/0x3c0 [bluetooth]
[<ffffffffa00150f7>] hci_event_packet+0xc7/0x29b0 [bluetooth]
[<ffffffff81202e90>] ? __dynamic_pr_debug+0x80/0x90
[<ffffffff8133ff7d>] ? kfree_skb+0x2d/0x40
[<ffffffffa0021644>] ? hci_send_to_monitor+0x1a4/0x1c0 [bluetooth]
[<ffffffffa0004583>] hci_rx_work+0x133/0x870 [bluetooth]
[<ffffffff8104d5f8>] ? process_one_work+0x258/0x4f0
[<ffffffff8104d65f>] process_one_work+0x2bf/0x4f0
[<ffffffff8104d5f8>] ? process_one_work+0x258/0x4f0
[<ffffffff8104fdc1>] ? worker_thread+0x51/0x3e0
[<ffffffffa0004450>] ? hci_tx_work+0x800/0x800 [bluetooth]
[<ffffffff81050022>] worker_thread+0x2b2/0x3e0
[<ffffffff8104fd70>] ? busy_worker_rebind_fn+0x100/0x100
[<ffffffff81056021>] kthread+0xd1/0xe0
[<ffffffff81055f50>] ? flush_kthread_worker+0xc0/0xc0
[<ffffffff813f14bc>] ret_from_fork+0x7c/0xb0
[<ffffffff81055f50>] ? flush_kthread_worker+0xc0/0xc0
Signed-off-by: Andre Guedes <andre.guedes@xxxxxxxxxxxxx>
---
This lockdep warning has been around for a long time. I could test
until Linux 3.4, but it seems it is older than that. However, in
current bluetooth-next, this warning has been masked by commit
53502d69be49e3dd5bc95ab0f2deeaea260bd617 which introduced a bug in
SCO hci_conn timeout routine.
The bug in SCO hci_conn timeout has been fixed by patch 01/03 from
this patchset.
net/bluetooth/sco.c | 18 ++++++++++--------
1 file changed, 10 insertions(+), 8 deletions(-)
diff --git a/net/bluetooth/sco.c b/net/bluetooth/sco.c
index 531a93d..e435641 100644
--- a/net/bluetooth/sco.c
+++ b/net/bluetooth/sco.c
@@ -900,8 +900,6 @@ static void sco_conn_ready(struct sco_conn *conn)
BT_DBG("conn %p", conn);
- sco_conn_lock(conn);
-
if (sk) {
sco_sock_clear_timer(sk);
bh_lock_sock(sk);
@@ -909,9 +907,13 @@ static void sco_conn_ready(struct sco_conn *conn)
sk->sk_state_change(sk);
bh_unlock_sock(sk);
} else {
+ sco_conn_lock(conn);
+
parent = sco_get_sock_listen(conn->src);
- if (!parent)
- goto done;
+ if (!parent) {
+ sco_conn_unlock(conn);
+ return;
+ }
bh_lock_sock(parent);
@@ -919,7 +921,8 @@ static void sco_conn_ready(struct sco_conn *conn)
BTPROTO_SCO, GFP_ATOMIC);
if (!sk) {
bh_unlock_sock(parent);
- goto done;
+ sco_conn_unlock(conn);
+ return;
}
sco_sock_init(sk, parent);
@@ -939,10 +942,9 @@ static void sco_conn_ready(struct sco_conn *conn)
parent->sk_data_ready(parent, 1);
bh_unlock_sock(parent);
- }
-done:
- sco_conn_unlock(conn);
+ sco_conn_unlock(conn);
+ }
}
/* ----- SCO interface with lower layer (HCI) ----- */
--
1.8.1.1
--
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