On 04/11/2017 04:13 PM, Rolf Evers-Fischer wrote:
Hi,
Christian Gromm <christian.gr...@xxxxxxxxxxxxx> writes:
we observe an issue with a td_list running empty and an
endpoint being stalled at the same time on
Linux ihu-low 4.1.27-abl #1 SMP PREEMPT Mon Mar 20 13:51:51 CET 2017
x86_64 x86_64 x86_64 GNU/Linux.
we've recently observed the same problem with "Linux ihu-low 4.1.27-abl" kernel.
In our case it was discovered from the logs that URBs, that are being killed by “usb_kill_anchored_urbs()”, are still being used by “handle_tx_event()”. Sooner or later the same URB was used and killed at the same time, which caused the “WARN Event TRB for slot 2 ep 28 with no TDs queued?” error message, and the whole communication stopped.
Well, this sounds like a workaround to me as you are changing the timing
by waiting for the URBs to finish. This might prevent the
race from happening.
I thought an USB device driver is allowed to kill anchored URBs at any
time, isn't it?
thanks,
Chris
The developer, who introduced the USB anchors, has added some demo code in the file drivers/usb/usb-skeleton.c. In this file he is invoking “usb_wait_anchor_empty_timeout()” before he calls “usb_kill_anchored_urbs()”. If I understand it correctly, the purpose of this function is to wait until all URBs have been processed.
Therefore I suggested to do the same in the most driver. Fortunately it seems that this resolved our problem: We've never seen this problem anymore.
BR
Rolf
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