Hi Abhishek,
> Unregister from suspend notifications and cancel suspend preparations
> before running hci_dev_do_close. Otherwise, the suspend notifier may
> race with unregister and cause cmd_timeout even after hdev has been
> freed.
>
> Below is the trace from when this panic was seen:
>
> [ 832.578518] Bluetooth: hci_core.c:hci_cmd_timeout() hci0: command 0x0c05 tx timeout
> [ 832.586200] BUG: kernel NULL pointer dereference, address: 0000000000000000
> [ 832.586203] #PF: supervisor read access in kernel mode
> [ 832.586205] #PF: error_code(0x0000) - not-present page
> [ 832.586206] PGD 0 P4D 0
> [ 832.586210] PM: suspend exit
> [ 832.608870] Oops: 0000 [#1] PREEMPT SMP NOPTI
> [ 832.613232] CPU: 3 PID: 10755 Comm: kworker/3:7 Not tainted 5.4.44-04894-g1e9dbb96a161 #1
> [ 832.630036] Workqueue: events hci_cmd_timeout [bluetooth]
> [ 832.630046] RIP: 0010:__queue_work+0xf0/0x374
> [ 832.630051] RSP: 0018:ffff9b5285f1fdf8 EFLAGS: 00010046
> [ 832.674033] RAX: ffff8a97681bac00 RBX: 0000000000000000 RCX: ffff8a976a000600
> [ 832.681162] RDX: 0000000000000000 RSI: 0000000000000009 RDI: ffff8a976a000748
> [ 832.688289] RBP: ffff9b5285f1fe38 R08: 0000000000000000 R09: ffff8a97681bac00
> [ 832.695418] R10: 0000000000000002 R11: ffff8a976a0006d8 R12: ffff8a9745107600
> [ 832.698045] usb 1-6: new full-speed USB device number 119 using xhci_hcd
> [ 832.702547] R13: ffff8a9673658850 R14: 0000000000000040 R15: 000000000000001e
> [ 832.702549] FS: 0000000000000000(0000) GS:ffff8a976af80000(0000) knlGS:0000000000000000
> [ 832.702550] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 832.702550] CR2: 0000000000000000 CR3: 000000010415a000 CR4: 00000000003406e0
> [ 832.702551] Call Trace:
> [ 832.702558] queue_work_on+0x3f/0x68
> [ 832.702562] process_one_work+0x1db/0x396
> [ 832.747397] worker_thread+0x216/0x375
> [ 832.751147] kthread+0x138/0x140
> [ 832.754377] ? pr_cont_work+0x58/0x58
> [ 832.758037] ? kthread_blkcg+0x2e/0x2e
> [ 832.761787] ret_from_fork+0x22/0x40
> [ 832.846191] ---[ end trace fa93f466da517212 ]---
>
> Fixes: 9952d90ea2885 ("Bluetooth: Handle PM_SUSPEND_PREPARE and PM_POST_SUSPEND")
> Signed-off-by: Abhishek Pandit-Subedi <abhishekpandit@xxxxxxxxxxxx>
> Reviewed-by: Miao-chen Chou <mcchou@xxxxxxxxxxxx>
> ---
> Hi Marcel,
>
> This fixes a race between hci_unregister_dev and the suspend notifier.
>
> The suspend notifier handler seemed to be scheduling commands even after
> it was cleaned up and this was resulting in a panic in cmd_timeout (when
> it tries to requeue the cmd_timer).
>
> This was tested on 5.4 kernel with a suspend+resume stress test for 500+
> iterations. I also confirmed that after a usb disconnect, the suspend
> notifier times out before the USB device is probed again (fixing the
> original race between the usb_disconnect + probe and the notifier).
>
> Thanks
> Abhishek
>
>
> Changes in v3:
> * Added fixes tag
>
> Changes in v2:
> * Moved oops into commit message
>
> net/bluetooth/hci_core.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
patch has been applied to bluetooth-next tree.
Regards
Marcel
