linux-kernel - [PATCH v4 0/3] Avoid having pending end transfers on soft disconnect

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Message-ID: <20230413195317.7468-1-quic_wcheng@quicinc.com>
Date:   Thu, 13 Apr 2023 12:53:14 -0700
From:   Wesley Cheng <quic_wcheng@...cinc.com>
To:     <gregkh@...uxfoundation.org>, <Thinh.Nguyen@...opsys.com>
CC:     <linux-kernel@...r.kernel.org>, <linux-usb@...r.kernel.org>,
        Wesley Cheng <quic_wcheng@...cinc.com>
Subject: [PATCH v4 0/3] Avoid having pending end transfers on soft disconnect

In case there is a host which takes time to complete a SETUP transaction,
during the soft disconnect sequence multiple DWC3 EPs will have their
DWC3_EP_DELAY_STOP flag set w/o issuing the end transfer command.  Once the
controller halt sequence occurs, the soft disconnect is successful, and
the subsequent soft connect will attempt to flush the pending end transfers.

Soft disconnect sequence:
  dwc3_gadget_ep_disable   name=ep8in flags=0x3009  direction=1
  dwc3_gadget_ep_disable   name=ep4in flags=1  direction=1
  dwc3_gadget_ep_disable   name=ep3out flags=1  direction=0
  usb_gadget_disconnect   deactivated=0  connected=0  ret=0

Soft connect bug:
  BUG: spinlock already unlocked on CPU
  spin_bug+0x0
  dwc3_remove_requests+0x278
  dwc3_ep0_out_start+0xb0
  __dwc3_gadget_start+0x25c

The bug occurs due to the flush of the pending end transfers, as the gadget
start routine is not held with a spinlock.  However, if the DWC3_EP_DELAY_STOP
is set, it will call the giveback API, which attempts to unlock the dwc->lock.
Ideally, the DWC3 gadget should not have pending end transfers on a soft
connect, so fix this by:

 1. Re-locating the SETUP phase check after stop active transfers, since
 that is where the DWC3_EP_DELAY_STOP is potentially set.  This also allows
 for handling of a host that may be unresponsive by using the completion
 timeout to trigger the stall and restart for EP0.

 2. Do not call gadget stop until the poll for controller halt is
 completed.  DEVTEN is cleared as part of gadget stop, so the intention to
 allow ep0 events to continue while waiting for controller halt is not
 happening.

Changes in v4:
- Added stable to patches that address the actual issue
- Re-ordered patch series to include the refactor change at the end to remove
  any dependencies to the actual fix.

Changes in v3:
- Removed fixes tag in the refactor change

Wesley Cheng (3):
  usb: dwc3: gadget: Stall and restart EP0 if host is unresponsive
  usb: dwc3: gadget: Execute gadget stop after halting the controller
  usb: dwc3: gadget: Refactor EP0 forced stall/restart into a separate
    API

 drivers/usb/dwc3/gadget.c | 101 ++++++++++++++++++++++----------------
 1 file changed, 58 insertions(+), 43 deletions(-)