Re: [RFC][PATCH] dwc3: gadget: Fix losing list items in dwc3_gadget_ep_cleanup_completed_requests()

[Thinh Nguyen <Thinh.Nguyen@synopsys.com>]

Hi Wesley,

Thinh Nguyen wrote:
> Thinh Nguyen wrote:
>> Wesley Cheng wrote:
>>> Hi Thinh,
>>>
>>> On 8/9/2021 3:57 PM, Thinh Nguyen wrote:
>>>> John Stultz wrote:
>>>>> On Mon, Aug 9, 2021 at 3:44 PM Thinh Nguyen <Thinh.Nguyen@synopsys.com> wrote:
>>>>>>
>>>>>> John Stultz wrote:
>>>>>>> In commit d25d85061bd8 ("usb: dwc3: gadget: Use
>>>>>>> list_replace_init() before traversing lists"), a local list_head
>>>>>>> was introduced to process the started_list items to avoid races.
>>>>>>>
>>>>>>> However, in dwc3_gadget_ep_cleanup_completed_requests() if
>>>>>>> dwc3_gadget_ep_cleanup_completed_request() fails, we break early,
>>>>>>> causing the items on the local list_head to be lost.
>>>>>>>
>>>>>>> This issue showed up as problems on the db845c/RB3 board, where
>>>>>>> adb connetions would fail, showing the device as "offline".
>>>>>>>
>>>>>>> This patch tries to fix the issue by if we are returning early
>>>>>>> we splice in the local list head back into the started_list
>>>>>>> and return (avoiding an infinite loop, as the started_list is
>>>>>>> now non-null).
>>>>>>>
>>>>>>> Not sure if this is fully correct, but seems to work for me so I
>>>>>>> wanted to share for feedback.
>>>>>>>
>>>>>>> Cc: Wesley Cheng <wcheng@codeaurora.org>
>>>>>>> Cc: Felipe Balbi <balbi@kernel.org>
>>>>>>> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>>>>>>> Cc: Alan Stern <stern@rowland.harvard.edu>
>>>>>>> Cc: Jack Pham <jackp@codeaurora.org>
>>>>>>> Cc: Thinh Nguyen <thinh.nguyen@synopsys.com>
>>>>>>> Cc: Todd Kjos <tkjos@google.com>
>>>>>>> Cc: Amit Pundir <amit.pundir@linaro.org>
>>>>>>> Cc: YongQin Liu <yongqin.liu@linaro.org>
>>>>>>> Cc: Sumit Semwal <sumit.semwal@linaro.org>
>>>>>>> Cc: Petri Gynther <pgynther@google.com>
>>>>>>> Cc: linux-usb@vger.kernel.org
>>>>>>> Fixes: d25d85061bd8 ("usb: dwc3: gadget: Use list_replace_init() before traversing lists")
>>>>>>> Signed-off-by: John Stultz <john.stultz@linaro.org>
>>>>>>> ---
>>>>>>>  drivers/usb/dwc3/gadget.c | 6 ++++++
>>>>>>>  1 file changed, 6 insertions(+)
>>>>>>>
>>>>>>> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
>>>>>>> index b8d4b2d327b23..a73ebe8e75024 100644
>>>>>>> --- a/drivers/usb/dwc3/gadget.c
>>>>>>> +++ b/drivers/usb/dwc3/gadget.c
>>>>>>> @@ -2990,6 +2990,12 @@ static void dwc3_gadget_ep_cleanup_completed_requests(struct dwc3_ep *dep,
>>>>>>>                       break;
>>>>>>>       }
>>>>>>>
>>>>>>> +     if (!list_empty(&local)) {
>>>>>>> +             list_splice_tail(&local, &dep->started_list);
>>>>>>> +             /* Return so we don't hit the restart case and loop forever */
>>>>>>> +             return;
>>>>>>> +     }
>>>>>>> +
>>>>>>>       if (!list_empty(&dep->started_list))
>>>>>>>               goto restart;
>>>>>>>  }
>>>>>>>
>>>>>>
>>>>>> No, we should revert the change for
>>>>>> dwc3_gadget_ep_cleaup_completed_requests(). As I mentioned previously,
>>>>>> we don't cleanup the entire started_list. If the original problem is due
>>>>>> to disconnection in the middle of request completion, then we can just
>>>>>> check for pullup_connected and exit the loop and let the
>>>>>> dwc3_remove_requests() do the cleanup.
>>>>>
>>>>> Ok, sorry, I didn't read your mail in depth until I had this patch
>>>>> sent out. If a revert of d25d85061bd8 is the better fix, I'm fine with
>>>>> that too.
>>>>>
>>>>> thanks
>>>>> -john
>>>>>
>>>>
>>>> IMO, we should revert this patch for now since it will cause regression.
>>>> We can review and test a proper fix at a later time.
>>>>
>>>> Thanks,
>>>> Thinh
>>>>
>>>
>>> Another suggestion would just be to replace the loop with a while() loop
>>> and using list_entry() instead.  That was what was discussed in the
>>> earlier patch series which also addresses the problem as well.  Issue
>>> here is the tmp variable still carries a stale request after the dwc3
>>> giveback is called.  We can avoid that by always fetching the
>>> list_entry() instead of relying on list_for_each_safe()
>>>
>>> https://urldefense.com/v3/__https://lore.kernel.org/linux-usb/1620716636-12422-1-git-send-email-wcheng@codeaurora.org/__;!!A4F2R9G_pg!P0E1pv3C0PStDepKyy8iqKgUaOhDy0ZDhYdz-_cZwnJRQjNjvw0MdJQCdU6Xwnt3YAs_$ 
>>>
>>
>> This should work, but the awkward thing is 2 loops from 2 separate
>> threads competing to remove/giveback the requests and may report mix status.
>>


Can you try this?

diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
index 706246d93a00..17b2d8d4efb4 100644
--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -2029,6 +2029,13 @@ static void dwc3_gadget_ep_cleanup_cancelled_requests(struct dwc3_ep *dep)
                        dwc3_gadget_giveback(dep, req, -ECONNRESET);
                        break;
                }
+
+               /*
+                * The endpoint is disabled, let the dwc3_remove_requests()
+                * handle the cleanup.
+                */
+               if (!dep->endpoint.desc)
+                       break;
        }
 }
 
@@ -3402,6 +3409,13 @@ static void dwc3_gadget_ep_cleanup_completed_requests(struct dwc3_ep *dep,
                                req, status);
                if (ret)
                        break;
+
+               /*
+                * The endpoint is disabled, let the dwc3_remove_requests()
+                * handle the cleanup.
+                */
+               if (!dep->endpoint.desc)
+                       break;
        }
 }

If needed, you can also use your change while(!list_empty(started_list)) along with this for future proof.

BR,
Thinh