[PATCH 0/1] usb: dwc2: Fix NULL qh in dwc2_queue_transaction

Alexandru M Stan amstan at chromium.org
Tue Sep 22 13:10:50 PDT 2015

I have a weird usb device which doesn't a normal connector, so there's
no guarantee that the pins will get removed in the correct order (data
pins first, then ground and vcc). I wouldn't be mad if there was a
weird error or something at connect/disconnect, but in this case I can
actually get a kernel panic.

Part of the panic text:
[  143.654956] [<c044e818>] (dwc2_queue_transaction) from [<c044f3b4>] (dwc2_hcd_queue_transactions+0x24c/0x31c)
[  143.664868] [<c044f3b4>] (dwc2_hcd_queue_transactions) from [<c044f4dc>] (_dwc2_hcd_clear_tt_buffer_complete+0x58/0x68)
[  143.675648] [<c044f4dc>] (_dwc2_hcd_clear_tt_buffer_complete) from [<c04347ec>] (hub_tt_work+0x130/0x164)
[  143.685214] [<c04347ec>] (hub_tt_work) from [<c013768c>] (process_one_work+0x258/0x3c0)
[  143.693217] [<c013768c>] (process_one_work) from [<c0138848>] (worker_thread+0x234/0x38c)
[  143.701394] [<c0138848>] (worker_thread) from [<c013e3dc>] (kthread+0xe4/0xfc)
[  143.708618] [<c013e3dc>] (kthread) from [<c0106278>] (ret_from_fork+0x14/0x20)

I traced it down to a dereference of qh(chan->qh->ping_state) in

At usb device disconnect, dwc2_hcd_cleanup_channels gets called,
which sets qh to NULL, but dwc2_queue_transaction still manages to
get called after that.

I can reproduce this in an isolated manner on my rk3288 board
with an FTDI/prolific device, having the usb pins easily
disconnectable(independently), then playing with the vcc pin while
leaving the data lines connected.

While my patch is probably not a proper fix for this issue, it's pretty
harmless where it is (and it's consistent with other checks in there).
I also hope this opens up discussions on this issue.

Alexandru M Stan (1):
  usb: dwc2: Fix NULL qh in dwc2_queue_transaction

 drivers/usb/dwc2/hcd.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)


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