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Message-ID: <1327948307.1955.140.camel@aeonflux>
Subject: Re: [PATCH 1/2] Bluetooth: Fix potential deadlock
From: Marcel Holtmann <marcel@holtmann.org>
To: Andre Guedes <andre.guedes@openbossa.org>
Cc: linux-bluetooth@vger.kernel.org,
	Vinicius Costa Gomes <vinicius.gomes@openbossa.org>
Date: Mon, 30 Jan 2012 10:31:47 -0800
In-Reply-To: <1327704123-31313-1-git-send-email-andre.guedes@openbossa.org>
References: <1327704123-31313-1-git-send-email-andre.guedes@openbossa.org>
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Sender: linux-bluetooth-owner@vger.kernel.org
List-ID: <linux-bluetooth.vger.kernel.org>

Hi Andre,

> We don't need to use the _sync variant in hci_conn_hold and
> hci_conn_put to cancel conn->disc_work delayed work. This way
> we avoid potential deadlocks like this one reported by lockdep.
> 
> ======================================================
> [ INFO: possible circular locking dependency detected ]
> 3.2.0+ #1 Not tainted
> -------------------------------------------------------
> kworker/u:1/17 is trying to acquire lock:
>  (&hdev->lock){+.+.+.}, at: [<ffffffffa0041155>] hci_conn_timeout+0x62/0x158 [bluetooth]
> 
> but task is already holding lock:
>  ((&(&conn->disc_work)->work)){+.+...}, at: [<ffffffff81035751>] process_one_work+0x11a/0x2bf
> 
> which lock already depends on the new lock.
> 
> the existing dependency chain (in reverse order) is:
> 
> -> #2 ((&(&conn->disc_work)->work)){+.+...}:
>        [<ffffffff81057444>] lock_acquire+0x8a/0xa7
>        [<ffffffff81034ed1>] wait_on_work+0x3d/0xaa
>        [<ffffffff81035b54>] __cancel_work_timer+0xac/0xef
>        [<ffffffff81035ba4>] cancel_delayed_work_sync+0xd/0xf
>        [<ffffffffa00554b0>] smp_chan_create+0xde/0xe6 [bluetooth]
>        [<ffffffffa0056160>] smp_conn_security+0xa3/0x12d [bluetooth]
>        [<ffffffffa0053640>] l2cap_connect_cfm+0x237/0x2e8 [bluetooth]
>        [<ffffffffa004239c>] hci_proto_connect_cfm+0x2d/0x6f [bluetooth]
>        [<ffffffffa0046ea5>] hci_event_packet+0x29d1/0x2d60 [bluetooth]
>        [<ffffffffa003dde3>] hci_rx_work+0xd0/0x2e1 [bluetooth]
>        [<ffffffff810357af>] process_one_work+0x178/0x2bf
>        [<ffffffff81036178>] worker_thread+0xce/0x152
>        [<ffffffff81039a03>] kthread+0x95/0x9d
>        [<ffffffff812e7754>] kernel_thread_helper+0x4/0x10
> 
> -> #1 (slock-AF_BLUETOOTH-BTPROTO_L2CAP){+.+...}:
>        [<ffffffff81057444>] lock_acquire+0x8a/0xa7
>        [<ffffffff812e553a>] _raw_spin_lock_bh+0x36/0x6a
>        [<ffffffff81244d56>] lock_sock_nested+0x24/0x7f
>        [<ffffffffa004d96f>] lock_sock+0xb/0xd [bluetooth]
>        [<ffffffffa0052906>] l2cap_chan_connect+0xa9/0x26f [bluetooth]
>        [<ffffffffa00545f8>] l2cap_sock_connect+0xb3/0xff [bluetooth]
>        [<ffffffff81243b48>] sys_connect+0x69/0x8a
>        [<ffffffff812e6579>] system_call_fastpath+0x16/0x1b
> 
> -> #0 (&hdev->lock){+.+.+.}:
>        [<ffffffff81056d06>] __lock_acquire+0xa80/0xd74
>        [<ffffffff81057444>] lock_acquire+0x8a/0xa7
>        [<ffffffff812e3870>] __mutex_lock_common+0x48/0x38e
>        [<ffffffff812e3c75>] mutex_lock_nested+0x2a/0x31
>        [<ffffffffa0041155>] hci_conn_timeout+0x62/0x158 [bluetooth]
>        [<ffffffff810357af>] process_one_work+0x178/0x2bf
>        [<ffffffff81036178>] worker_thread+0xce/0x152
>        [<ffffffff81039a03>] kthread+0x95/0x9d
>        [<ffffffff812e7754>] kernel_thread_helper+0x4/0x10
> 
> other info that might help us debug this:
> 
> Chain exists of:
>   &hdev->lock --> slock-AF_BLUETOOTH-BTPROTO_L2CAP --> (&(&conn->disc_work)->work)
> 
>  Possible unsafe locking scenario:
> 
>        CPU0                    CPU1
>        ----                    ----
>   lock((&(&conn->disc_work)->work));
>                                lock(slock-AF_BLUETOOTH-BTPROTO_L2CAP);
>                                lock((&(&conn->disc_work)->work));
>   lock(&hdev->lock);
> 
>  *** DEADLOCK ***
> 
> 2 locks held by kworker/u:1/17:
>  #0:  (hdev->name){.+.+.+}, at: [<ffffffff81035751>] process_one_work+0x11a/0x2bf
>  #1:  ((&(&conn->disc_work)->work)){+.+...}, at: [<ffffffff81035751>] process_one_work+0x11a/0x2bf
> 
> stack backtrace:
> Pid: 17, comm: kworker/u:1 Not tainted 3.2.0+ #1
> Call Trace:
>  [<ffffffff812e06c6>] print_circular_bug+0x1f8/0x209
>  [<ffffffff81056d06>] __lock_acquire+0xa80/0xd74
>  [<ffffffff81021ef2>] ? arch_local_irq_restore+0x6/0xd
>  [<ffffffff81022bc7>] ? vprintk+0x3f9/0x41e
>  [<ffffffff81057444>] lock_acquire+0x8a/0xa7
>  [<ffffffffa0041155>] ? hci_conn_timeout+0x62/0x158 [bluetooth]
>  [<ffffffff812e3870>] __mutex_lock_common+0x48/0x38e
>  [<ffffffffa0041155>] ? hci_conn_timeout+0x62/0x158 [bluetooth]
>  [<ffffffff81190fd6>] ? __dynamic_pr_debug+0x6d/0x6f
>  [<ffffffffa0041155>] ? hci_conn_timeout+0x62/0x158 [bluetooth]
>  [<ffffffff8105320f>] ? trace_hardirqs_off+0xd/0xf
>  [<ffffffff812e3c75>] mutex_lock_nested+0x2a/0x31
>  [<ffffffffa0041155>] hci_conn_timeout+0x62/0x158 [bluetooth]
>  [<ffffffff810357af>] process_one_work+0x178/0x2bf
>  [<ffffffff81035751>] ? process_one_work+0x11a/0x2bf
>  [<ffffffff81055af3>] ? lock_acquired+0x1d0/0x1df
>  [<ffffffffa00410f3>] ? hci_acl_disconn+0x65/0x65 [bluetooth]
>  [<ffffffff81036178>] worker_thread+0xce/0x152
>  [<ffffffff810407ed>] ? finish_task_switch+0x45/0xc5
>  [<ffffffff810360aa>] ? manage_workers.isra.25+0x16a/0x16a
>  [<ffffffff81039a03>] kthread+0x95/0x9d
>  [<ffffffff812e7754>] kernel_thread_helper+0x4/0x10
>  [<ffffffff812e5db4>] ? retint_restore_args+0x13/0x13
>  [<ffffffff8103996e>] ? __init_kthread_worker+0x55/0x55
>  [<ffffffff812e7750>] ? gs_change+0x13/0x13
> 
> Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>
> Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@openbossa.org>
> ---
>  include/net/bluetooth/hci_core.h |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)

Reviewed-by: Ulisses Furquim <ulisses@profusion.mobi>
Acked-by: Marcel Holtmann <marcel@holtmann.org>

Regards

Marcel