linux-kernel - Re: [PATCH] usb: xhci-ring: set all cancelled_td's cancel_status to TD_CLEARING

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Message-ID: <a87c1d9563c03afb609543e7abe63708@codeaurora.org>
Date:   Fri, 13 Aug 2021 16:44:37 +0800
From:   wat@...eaurora.org
To:     Ikjoon Jang <ikjn@...omium.org>
Cc:     Mathias Nyman <mathias.nyman@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "open list:USB XHCI DRIVER" <linux-usb@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: xhci-ring: set all cancelled_td's cancel_status to
 TD_CLEARING_CACHE

On 2021-08-13 15:25, Ikjoon Jang wrote:
> Hi,
> 
> On Fri, Aug 13, 2021 at 10:44 AM Tao Wang <wat@...eaurora.org> wrote:
>> 
>> USB SSD may fail to unmount if disconnect during data transferring.
>> 
>> it stuck in usb_kill_urb() due to urb use_count will not become zero,
>> this means urb giveback is not happen.
>> in xhci_handle_cmd_set_deq() will giveback urb if td's cancel_status
>> equal to TD_CLEARING_CACHE,
>> but in xhci_invalidate_cancelled_tds(), only last canceled td's
>> cancel_status change to TD_CLEARING_CACHE,
>> thus giveback only happen to last urb.
>> 
>> this change set all cancelled_td's cancel_status to TD_CLEARING_CACHE
>> rather than the last one, so all urb can giveback.
>> 
>> Signed-off-by: Tao Wang <wat@...eaurora.org>
>> ---
>>  drivers/usb/host/xhci-ring.c | 24 ++++++++++++------------
>>  1 file changed, 12 insertions(+), 12 deletions(-)
>> 
>> diff --git a/drivers/usb/host/xhci-ring.c 
>> b/drivers/usb/host/xhci-ring.c
>> index 8fea44b..c7dd7c0 100644
>> --- a/drivers/usb/host/xhci-ring.c
>> +++ b/drivers/usb/host/xhci-ring.c
>> @@ -960,19 +960,19 @@ static int xhci_invalidate_cancelled_tds(struct 
>> xhci_virt_ep *ep)
>>                         td_to_noop(xhci, ring, td, false);
>>                         td->cancel_status = TD_CLEARED;
>>                 }
>> -       }
>> -       if (cached_td) {
>> -               cached_td->cancel_status = TD_CLEARING_CACHE;
>> -
>> -               err = xhci_move_dequeue_past_td(xhci, slot_id, 
>> ep->ep_index,
>> -                                               
>> cached_td->urb->stream_id,
>> -                                               cached_td);
>> -               /* Failed to move past cached td, try just setting it 
>> noop */
>> -               if (err) {
>> -                       td_to_noop(xhci, ring, cached_td, false);
>> -                       cached_td->cancel_status = TD_CLEARED;
>> +               if (cached_td) {
>> +                       cached_td->cancel_status = TD_CLEARING_CACHE;
>> +
>> +                       err = xhci_move_dequeue_past_td(xhci, slot_id, 
>> ep->ep_index,
>> +                                                       
>> cached_td->urb->stream_id,
>> +                                                       cached_td);
>> +                       /* Failed to move past cached td, try just 
>> setting it noop */
>> +                       if (err) {
>> +                               td_to_noop(xhci, ring, cached_td, 
>> false);
>> +                               cached_td->cancel_status = TD_CLEARED;
>> +                       }
>> +                       cached_td = NULL;
>>                 }
>> -               cached_td = NULL;
> 
> I think we can call xhci_move_dequeue_past_td() just once to
> the last halted && cancelled TD in a ring.
> 
> But that might need to compare two TDs to see which one is
> the latter, I'm not sure how to do this well. :-/
> 
> if (!cached_td || cached_td < td)
>   cached_td = td;
> 

thanks, I think you are correct that we can call 
xhci_move_dequeue_past_td() just once to
  the last halted && cancelled TD in a ring,
but the set status "cached_td->cancel_status = TD_CLEARING_CACHE;" 
should be every cancelled TD.
I am not very good at td and ring, I have a question why we need to
compare two TDs to see which one is the latter.

>>         }
>>         return 0;
>>  }
>> --
>> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora 
>> Forum,
>> a Linux Foundation Collaborative Project
>>