Commit eab2404b ("Bluetooth: Add BT_PHY socket option") added a
dependency between socket lock and hci_dev->lock that could lead to
deadlock.

It turns out that hci_conn_get_phy() is not in any way relying on hdev
being immutable during the runtime of this function, neither does it even
look at any of the members of hdev, and as such there is no need to hold
that lock.

This fixes the lockdep splat below:

 ======================================================
 WARNING: possible circular locking dependency detected
 5.12.0-rc1-00026-g73d464503354 #10 Not tainted
 ------------------------------------------------------
 bluetoothd/1118 is trying to acquire lock:
 ffff8f078383c078 (&hdev->lock){+.+.}-{3:3}, at: hci_conn_get_phy+0x1c/0x150 [bluetooth]

 but task is already holding lock:
 ffff8f07e831d920 (sk_lock-AF_BLUETOOTH-BTPROTO_L2CAP){+.+.}-{0:0}, at: l2cap_sock_getsockopt+0x8b/0x610

 which lock already depends on the new lock.

 the existing dependency chain (in reverse order) is:

 -> #3 (sk_lock-AF_BLUETOOTH-BTPROTO_L2CAP){+.+.}-{0:0}:
        lock_sock_nested+0x72/0xa0
        l2cap_sock_ready_cb+0x18/0x70 [bluetooth]
        l2cap_config_rsp+0x27a/0x520 [bluetooth]
        l2cap_sig_channel+0x658/0x1330 [bluetooth]
        l2cap_recv_frame+0x1ba/0x310 [bluetooth]
        hci_rx_work+0x1cc/0x640 [bluetooth]
        process_one_work+0x244/0x5f0
        worker_thread+0x3c/0x380
        kthread+0x13e/0x160
        ret_from_fork+0x22/0x30

 -> #2 (&chan->lock#2/1){+.+.}-{3:3}:
        __mutex_lock+0xa3/0xa10
        l2cap_chan_connect+0x33a/0x940 [bluetooth]
        l2cap_sock_connect+0x141/0x2a0 [bluetooth]
        __sys_connect+0x9b/0xc0
        __x64_sys_connect+0x16/0x20
        do_syscall_64+0x33/0x80
        entry_SYSCALL_64_after_hwframe+0x44/0xae

 -> #1 (&conn->chan_lock){+.+.}-{3:3}:
        __mutex_lock+0xa3/0xa10
        l2cap_chan_connect+0x322/0x940 [bluetooth]
        l2cap_sock_connect+0x141/0x2a0 [bluetooth]
        __sys_connect+0x9b/0xc0
        __x64_sys_connect+0x16/0x20
        do_syscall_64+0x33/0x80
        entry_SYSCALL_64_after_hwframe+0x44/0xae

 -> #0 (&hdev->lock){+.+.}-{3:3}:
        __lock_acquire+0x147a/0x1a50
        lock_acquire+0x277/0x3d0
        __mutex_lock+0xa3/0xa10
        hci_conn_get_phy+0x1c/0x150 [bluetooth]
        l2cap_sock_getsockopt+0x5a9/0x610 [bluetooth]
        __sys_getsockopt+0xcc/0x200
        __x64_sys_getsockopt+0x20/0x30
        do_syscall_64+0x33/0x80
        entry_SYSCALL_64_after_hwframe+0x44/0xae

 other info that might help us debug this:

 Chain exists of:
   &hdev->lock --> &chan->lock#2/1 --> sk_lock-AF_BLUETOOTH-BTPROTO_L2CAP

  Possible unsafe locking scenario:

        CPU0                    CPU1
        ----                    ----
   lock(sk_lock-AF_BLUETOOTH-BTPROTO_L2CAP);
                                lock(&chan->lock#2/1);
                                lock(sk_lock-AF_BLUETOOTH-BTPROTO_L2CAP);
   lock(&hdev->lock);

  *** DEADLOCK ***

 1 lock held by bluetoothd/1118:
  #0: ffff8f07e831d920 (sk_lock-AF_BLUETOOTH-BTPROTO_L2CAP){+.+.}-{0:0}, at: l2cap_sock_getsockopt+0x8b/0x610 [bluetooth]

 stack backtrace:
 CPU: 3 PID: 1118 Comm: bluetoothd Not tainted 5.12.0-rc1-00026-g73d464503354 #10
 Hardware name: LENOVO 20K5S22R00/20K5S22R00, BIOS R0IET38W (1.16 ) 05/31/2017
 Call Trace:
  dump_stack+0x7f/0xa1
  check_noncircular+0x105/0x120
  ? __lock_acquire+0x147a/0x1a50
  __lock_acquire+0x147a/0x1a50
  lock_acquire+0x277/0x3d0
  ? hci_conn_get_phy+0x1c/0x150 [bluetooth]
  ? __lock_acquire+0x2e1/0x1a50
  ? lock_is_held_type+0xb4/0x120
  ? hci_conn_get_phy+0x1c/0x150 [bluetooth]
  __mutex_lock+0xa3/0xa10
  ? hci_conn_get_phy+0x1c/0x150 [bluetooth]
  ? lock_acquire+0x277/0x3d0
  ? mark_held_locks+0x49/0x70
  ? mark_held_locks+0x49/0x70
  ? hci_conn_get_phy+0x1c/0x150 [bluetooth]
  hci_conn_get_phy+0x1c/0x150 [bluetooth]
  l2cap_sock_getsockopt+0x5a9/0x610 [bluetooth]
  __sys_getsockopt+0xcc/0x200
  __x64_sys_getsockopt+0x20/0x30
  do_syscall_64+0x33/0x80
  entry_SYSCALL_64_after_hwframe+0x44/0xae
 RIP: 0033:0x7fb73df33eee
 Code: 48 8b 0d 85 0f 0c 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa 49 89 ca b8 37 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 52 0f 0c 00 f7 d8 64 89 01 48
 RSP: 002b:00007fffcfbbbf08 EFLAGS: 00000203 ORIG_RAX: 0000000000000037
 RAX: ffffffffffffffda RBX: 0000000000000019 RCX: 00007fb73df33eee
 RDX: 000000000000000e RSI: 0000000000000112 RDI: 0000000000000018
 RBP: 0000000000000000 R08: 00007fffcfbbbf44 R09: 0000000000000000
 R10: 00007fffcfbbbf3c R11: 0000000000000203 R12: 0000000000000000
 R13: 0000000000000018 R14: 0000000000000000 R15: 0000556fcefc70d0

Fixes: eab2404b ("Bluetooth: Add BT_PHY socket option")
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>