On Mon, Apr 15, 2024 at 11:26:00AM +0200, Bjørn Mork wrote: > Oliver Neukum <oneukum@xxxxxxxx> writes: > > On 15.04.24 08:47, Bjørn Mork wrote: > > > >> urb from service_outstanding_interrupt(). That's why it was added. See > >> the explanation Robert wrote when introducing it: > >> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/usb/class/cdc-wdm.c?id=c1da59dad0ebd3f9bd238f3fff82b1f7ffda7829 > > > > Well, the explanation is correct in that we must read > > data available. However, if the RESPONDING flag is set > > and the URB submitted, we are already doing so. > > Sounds reasonable. Except that the bug proves we didn't. > > If you are right that service_outstanding_interrupt can race againts > itself (and I don't doubt that), then I guess this could also happen > between failure to submit the URB and clearing the flag? > > >> As for the XMM behaviour: it's been a long time since I tried any of > >> those, but AFAIR one the major differences compared to Qualcomm was the > >> strict queue handling in the firmware. This caused a number of problems > >> where the cdc-wdm driver wanted to skip a message for some reason. So > >> I'm not surprised that a bug like this is triggered by one of those > >> modems. That's probably the only thing they are good for :-) > > > > I am not sure where exactly the issue lies here. Suggestions for > > debugging? > > Nothing more than the obvious; Get one of those modems and do some > usbmon snooping. So for now, should we just revert this problem commit? thanks, greg k-h
