Bluetooth: Shutdown controller after workqueues are flushed or cancelled

Bluetooth: Shutdown controller after workqueues are flushed or cancelled

Rfkill block and unblock Intel USB Bluetooth [8087:0026] may make it
stops working:
[  509.691509] Bluetooth: hci0: HCI reset during shutdown failed
[  514.897584] Bluetooth: hci0: MSFT filter_enable is already on
[  530.044751] usb 3-10: reset full-speed USB device number 5 using xhci_hcd
[  545.660350] usb 3-10: device descriptor read/64, error -110
[  561.283530] usb 3-10: device descriptor read/64, error -110
[  561.519682] usb 3-10: reset full-speed USB device number 5 using xhci_hcd
[  566.686650] Bluetooth: hci0: unexpected event for opcode 0x0500
[  568.752452] Bluetooth: hci0: urb 0000000096cd309b failed to resubmit (113)
[  578.797955] Bluetooth: hci0: Failed to read MSFT supported features (-110)
[  586.286565] Bluetooth: hci0: urb 00000000c522f633 failed to resubmit (113)
[  596.215302] Bluetooth: hci0: Failed to read MSFT supported features (-110)

Or kernel panics because other workqueues already freed skb:
[ 2048.663763] BUG: kernel NULL pointer dereference, address: 0000000000000000
[ 2048.663775] #PF: supervisor read access in kernel mode
[ 2048.663779] #PF: error_code(0x0000) - not-present page
[ 2048.663782] PGD 0 P4D 0
[ 2048.663787] Oops: 0000 [#1] SMP NOPTI
[ 2048.663793] CPU: 3 PID: 4491 Comm: rfkill Tainted: G        W         5.13.0-rc1-next-20210510+ #20
[ 2048.663799] Hardware name: HP HP EliteBook 850 G8 Notebook PC/8846, BIOS T76 Ver. 01.01.04 12/02/2020
[ 2048.663801] RIP: 0010:__skb_ext_put+0x6/0x50
[ 2048.663814] Code: 8b 1b 48 85 db 75 db 5b 41 5c 5d c3 be 01 00 00 00 e8 de 13 c0 ff eb e7 be 02 00 00 00 e8 d2 13 c0 ff eb db 0f 1f 44 00 00 55 <8b> 07 48 89 e5 83 f8 01 74 14 b8 ff ff ff ff f0 0f c1
07 83 f8 01
[ 2048.663819] RSP: 0018:ffffc1d105b6fd80 EFLAGS: 00010286
[ 2048.663824] RAX: 0000000000000000 RBX: ffff9d9ac5649000 RCX: 0000000000000000
[ 2048.663827] RDX: ffffffffc0d1daf6 RSI: 0000000000000206 RDI: 0000000000000000
[ 2048.663830] RBP: ffffc1d105b6fd98 R08: 0000000000000001 R09: ffff9d9ace8ceac0
[ 2048.663834] R10: ffff9d9ace8ceac0 R11: 0000000000000001 R12: ffff9d9ac5649000
[ 2048.663838] R13: 0000000000000000 R14: 00007ffe0354d650 R15: 0000000000000000
[ 2048.663843] FS:  00007fe02ab19740(0000) GS:ffff9d9e5f8c0000(0000) knlGS:0000000000000000
[ 2048.663849] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 2048.663853] CR2: 0000000000000000 CR3: 0000000111a52004 CR4: 0000000000770ee0
[ 2048.663856] PKRU: 55555554
[ 2048.663859] Call Trace:
[ 2048.663865]  ? skb_release_head_state+0x5e/0x80
[ 2048.663873]  kfree_skb+0x2f/0xb0
[ 2048.663881]  btusb_shutdown_intel_new+0x36/0x60 [btusb]
[ 2048.663905]  hci_dev_do_close+0x48c/0x5e0 [bluetooth]
[ 2048.663954]  ? __cond_resched+0x1a/0x50
[ 2048.663962]  hci_rfkill_set_block+0x56/0xa0 [bluetooth]
[ 2048.664007]  rfkill_set_block+0x98/0x170
[ 2048.664016]  rfkill_fop_write+0x136/0x1e0
[ 2048.664022]  vfs_write+0xc7/0x260
[ 2048.664030]  ksys_write+0xb1/0xe0
[ 2048.664035]  ? exit_to_user_mode_prepare+0x37/0x1c0
[ 2048.664042]  __x64_sys_write+0x1a/0x20
[ 2048.664048]  do_syscall_64+0x40/0xb0
[ 2048.664055]  entry_SYSCALL_64_after_hwframe+0x44/0xae
[ 2048.664060] RIP: 0033:0x7fe02ac23c27
[ 2048.664066] Code: 0d 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b7 0f 1f 00 f3 0f 1e fa 64 8b 04 25 18 00 00 00 85 c0 75 10 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 51 c3 48 83 ec 28 48 89 54 24 18 48 89 74 24
[ 2048.664070] RSP: 002b:00007ffe0354d638 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
[ 2048.664075] RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 00007fe02ac23c27
[ 2048.664078] RDX: 0000000000000008 RSI: 00007ffe0354d650 RDI: 0000000000000003
[ 2048.664081] RBP: 0000000000000000 R08: 0000559b05998440 R09: 0000559b05998440
[ 2048.664084] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000003
[ 2048.664086] R13: 0000000000000000 R14: ffffffff00000000 R15: 00000000ffffffff

So move the shutdown callback to a place where workqueues are either
flushed or cancelled to resolve the issue.

Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>