• Ulisses Furquim's avatar
    Bluetooth: Fix deadlocks with sock lock and L2CAP timers locks · 371fd835
    Ulisses Furquim authored
    When cancelling a delayed work (timer) in L2CAP we can not sleep holding
    the sock mutex otherwise we might deadlock with an L2CAP timer handler.
    This is possible because RX/TX and L2CAP timers run in different workqueues.
    The scenario below illustrates the problem. Thus we are now avoiding to
    sleep on the timers locks.
    
     ======================================================
     [ INFO: possible circular locking dependency detected ]
     3.1.0-05270-ga978dc7-dirty #239
     -------------------------------------------------------
     kworker/1:1/873 is trying to acquire lock:
      (sk_lock-AF_BLUETOOTH-BTPROTO_L2CAP){+.+...}, at: [<ffffffffa002ceac>] l2cap_chan_timeout+0x3c/0xe0 [bluetooth]
    
     but task is already holding lock:
      ((&(&chan->chan_timer)->work)){+.+...}, at: [<ffffffff81051a86>] process_one_work+0x126/0x450
    
     which lock already depends on the new lock.
    
     the existing dependency chain (in reverse order) is:
    
     -> #1 ((&(&chan->chan_timer)->work)){+.+...}:
            [<ffffffff8106b276>] check_prevs_add+0xf6/0x170
            [<ffffffff8106b903>] validate_chain+0x613/0x790
            [<ffffffff8106dfee>] __lock_acquire+0x4be/0xac0
            [<ffffffff8106ec2d>] lock_acquire+0x8d/0xb0
            [<ffffffff81052a6f>] wait_on_work+0x4f/0x160
            [<ffffffff81052ca3>] __cancel_work_timer+0x73/0x80
            [<ffffffff81052cbd>] cancel_delayed_work_sync+0xd/0x10
            [<ffffffffa002f2ed>] l2cap_chan_connect+0x22d/0x470 [bluetooth]
            [<ffffffffa002fb51>] l2cap_sock_connect+0xb1/0x140 [bluetooth]
            [<ffffffff8130811b>] kernel_connect+0xb/0x10
            [<ffffffffa00cf98a>] rfcomm_session_create+0x12a/0x1c0 [rfcomm]
            [<ffffffffa00cfbe7>] __rfcomm_dlc_open+0x1c7/0x240 [rfcomm]
            [<ffffffffa00d07c2>] rfcomm_dlc_open+0x42/0x70 [rfcomm]
            [<ffffffffa00d3b03>] rfcomm_sock_connect+0x103/0x150 [rfcomm]
            [<ffffffff8130bd7e>] sys_connect+0xae/0xc0
            [<ffffffff813368d2>] compat_sys_socketcall+0xb2/0x220
            [<ffffffff813b2089>] sysenter_dispatch+0x7/0x30
    
     -> #0 (sk_lock-AF_BLUETOOTH-BTPROTO_L2CAP){+.+...}:
            [<ffffffff8106b16d>] check_prev_add+0x6cd/0x6e0
            [<ffffffff8106b276>] check_prevs_add+0xf6/0x170
            [<ffffffff8106b903>] validate_chain+0x613/0x790
            [<ffffffff8106dfee>] __lock_acquire+0x4be/0xac0
            [<ffffffff8106ec2d>] lock_acquire+0x8d/0xb0
            [<ffffffff8130d91a>] lock_sock_nested+0x8a/0xa0
            [<ffffffffa002ceac>] l2cap_chan_timeout+0x3c/0xe0 [bluetooth]
            [<ffffffff81051ae4>] process_one_work+0x184/0x450
            [<ffffffff8105276e>] worker_thread+0x15e/0x340
            [<ffffffff81057bb6>] kthread+0x96/0xa0
            [<ffffffff813b1ef4>] kernel_thread_helper+0x4/0x10
    
     other info that might help us debug this:
    
      Possible unsafe locking scenario:
    
            CPU0                    CPU1
            ----                    ----
       lock((&(&chan->chan_timer)->work));
                                    lock(sk_lock-AF_BLUETOOTH-BTPROTO_L2CAP);
                                    lock((&(&chan->chan_timer)->work));
       lock(sk_lock-AF_BLUETOOTH-BTPROTO_L2CAP);
    
      *** DEADLOCK ***
    
     2 locks held by kworker/1:1/873:
      #0:  (events){.+.+.+}, at: [<ffffffff81051a86>] process_one_work+0x126/0x450
      #1:  ((&(&chan->chan_timer)->work)){+.+...}, at: [<ffffffff81051a86>] process_one_work+0x126/0x450
    
     stack backtrace:
     Pid: 873, comm: kworker/1:1 Not tainted 3.1.0-05270-ga978dc7-dirty #239
     Call Trace:
      [<ffffffff813a0f6e>] print_circular_bug+0xd2/0xe3
      [<ffffffff8106b16d>] check_prev_add+0x6cd/0x6e0
      [<ffffffff8106b276>] check_prevs_add+0xf6/0x170
      [<ffffffff8106b903>] validate_chain+0x613/0x790
      [<ffffffff8106dfee>] __lock_acquire+0x4be/0xac0
      [<ffffffff8130d8f6>] ? lock_sock_nested+0x66/0xa0
      [<ffffffff8106ea30>] ? lock_release_nested+0x100/0x110
      [<ffffffff8130d8f6>] ? lock_sock_nested+0x66/0xa0
      [<ffffffff8106ec2d>] lock_acquire+0x8d/0xb0
      [<ffffffffa002ceac>] ? l2cap_chan_timeout+0x3c/0xe0 [bluetooth]
      [<ffffffff8130d91a>] lock_sock_nested+0x8a/0xa0
      [<ffffffffa002ceac>] ? l2cap_chan_timeout+0x3c/0xe0 [bluetooth]
      [<ffffffff81051a86>] ? process_one_work+0x126/0x450
      [<ffffffffa002ceac>] l2cap_chan_timeout+0x3c/0xe0 [bluetooth]
      [<ffffffff81051ae4>] process_one_work+0x184/0x450
      [<ffffffff81051a86>] ? process_one_work+0x126/0x450
      [<ffffffffa002ce70>] ? l2cap_security_cfm+0x4e0/0x4e0 [bluetooth]
      [<ffffffff8105276e>] worker_thread+0x15e/0x340
      [<ffffffff81052610>] ? manage_workers+0x110/0x110
      [<ffffffff81057bb6>] kthread+0x96/0xa0
      [<ffffffff813b1ef4>] kernel_thread_helper+0x4/0x10
      [<ffffffff813af69d>] ? retint_restore_args+0xe/0xe
      [<ffffffff81057b20>] ? __init_kthread_worker+0x70/0x70
      [<ffffffff813b1ef0>] ? gs_change+0xb/0xb
    Signed-off-by: default avatarUlisses Furquim <ulisses@profusion.mobi>
    Acked-by: default avatarMarcel Holtmann <marcel@holtmann.org>
    Signed-off-by: default avatarGustavo F. Padovan <padovan@profusion.mobi>
    371fd835
l2cap_core.c 107 KB