On 21-05-08 01:15:49, Wesley Cheng wrote:
>
>
> 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.
It is cleared now. Would you please update commit log a little by appending
your call stack analysis?
Reviewed-by: Peter Chen <peter.chen@xxxxxxxxxx>
Peter
>
> 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
--
Thanks,
Peter Chen
