On 5/7/2021 8:45 PM, Peter Chen wrote:
> On 21-05-07 11:42:03, Wesley Cheng wrote:
>> The list_for_each_entry_safe() macro saves the current item (n) and
>> the item after (n+1), so that n can be safely removed without
>> corrupting the list. However, when traversing the list and removing
>> items using gadget giveback, the DWC3 lock is briefly released,
Hi Peter,
Thanks for the review.
>
> I see dwc3_gadget_del_and_unmap_request remove the list, the lock is
> still held there. Am I something wrong?
>
The scenario the issue happens in is say the follow thread is running
the sequence below:
Thread#1:
__dwc3_gadget_ep_set_halt() - CLEAR HALT
-> dwc3_gadget_ep_cleanup_cancelled_requests()
->list_for_each_entry_safe()
->dwc3_gadget_giveback()
->dwc3_gadget_del_and_unmap_request()-n deleted cancelled_list
->spin_unlock
Thread#2:
dwc3_gadget_pullup()
->waiting for dwc3 spin_lock
->Thread#1 released lock
->dwc3_stop_active_transfers()
->dwc3_remove_requests()
->fetches n+1 item from cancelled_list (n removed by thread#1)
->dwc3_gadget_giveback()
->dwc3_gadget_del_and_unmap_request()-n+1 deleted cancelled_list
->spin_unlock
So now, if thread#1 takes the DWC3 lock again, it will continue to item
n+1, which was already removed by thread#2, leading to a double list
removal. We saw this issue on our platform after enabling list debug.
Thanks
Wesley Cheng
> Peter
>
>> allowing other routines to execute. There is a situation where while
>> items are being removed from the cancelled_list using
>> dwc3_gadget_ep_cleanup_cancelled_requests(), the pullup disable
>> routine is running in parallel (due to UDC unbind). As the cleanup
>> routine removes n, and the pullup disable removes n+1, once the
>> cleanup retakes the DWC3 lock, it references a request who was already
>> removed/handled. With list debug enabled, this leads to a panic.
>> Ensure all instances of the macro are replaced where gadget giveback
>> is used.
>>
>> Fixes: d4f1afe5e896 ("usb: dwc3: gadget: move requests to cancelled_list")
>> Signed-off-by: Wesley Cheng <wcheng@xxxxxxxxxxxxxx>
>> ---
>> drivers/usb/dwc3/gadget.c | 8 ++++----
>> 1 file changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
>> index dd80e5c..efa939b 100644
>> --- a/drivers/usb/dwc3/gadget.c
>> +++ b/drivers/usb/dwc3/gadget.c
>> @@ -1737,10 +1737,10 @@ static void dwc3_gadget_ep_skip_trbs(struct dwc3_ep *dep, struct dwc3_request *r
>> static void dwc3_gadget_ep_cleanup_cancelled_requests(struct dwc3_ep *dep)
>> {
>> struct dwc3_request *req;
>> - struct dwc3_request *tmp;
>> struct dwc3 *dwc = dep->dwc;
>>
>> - list_for_each_entry_safe(req, tmp, &dep->cancelled_list, list) {
>> + while (!list_empty(&dep->cancelled_list)) {
>> + req = next_request(&dep->cancelled_list);
>> dwc3_gadget_ep_skip_trbs(dep, req);
>> switch (req->status) {
>> case DWC3_REQUEST_STATUS_DISCONNECTED:
>> @@ -2935,11 +2935,11 @@ static void dwc3_gadget_ep_cleanup_completed_requests(struct dwc3_ep *dep,
>> const struct dwc3_event_depevt *event, int status)
>> {
>> struct dwc3_request *req;
>> - struct dwc3_request *tmp;
>>
>> - list_for_each_entry_safe(req, tmp, &dep->started_list, list) {
>> + while (!list_empty(&dep->started_list)) {
>> int ret;
>>
>> + req = next_request(&dep->started_list);
>> ret = dwc3_gadget_ep_cleanup_completed_request(dep, event,
>> req, status);
>> if (ret)
>> --
>> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
>> a Linux Foundation Collaborative Project
>>
>
--
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project
