On Sun, May 01, 2022 at 08:58:28PM +0300, Sergey Ryazanov wrote: > cdc-wdm tracks whether a response reading request is in-progress and > blocks the next request from being sent until the previous request is > completed. As soon as last user closes the cdc-wdm device file, the > driver cancels any ongoing requests, resets the pending response > counter, but leaves the response reading in-progress flag > (WDM_RESPONDING) untouched. > > So if the user closes the device file during the response receive > request is being performed, no more data will be obtained from the > modem. The request will be cancelled, effectively preventing the > WDM_RESPONDING flag from being reseted. Keeping the flag set will > prevent a new response receive request from being sent, permanently > blocking the read path. The read path will staying blocked until the > module will be reloaded or till the modem will be re-attached. > > This stuck has been observed with a Huawei E3372 modem attached to an > OpenWrt router and using the comgt utility to set up a network > connection. > > Fix this issue by clearing the WDM_RESPONDING flag on the device file > close. > > Without this fix, the device reading stuck can be easily reproduced in a > few connection establishing attempts. With this fix, a load test for > modem connection re-establishing worked for several hours without any > issues. > > Fixes: 922a5eadd5a3 ("usb: cdc-wdm: Fix race between autosuspend and > reading from the device") Nit, Fixes: lines should only be one line, I'll fix this up when applying it. > Signed-off-by: Sergey Ryazanov <ryazanov.s.a@xxxxxxxxx> > --- > > Technically, cdc-wdm belongs to the USB subsystem even though it serves > WWAN devices. I think this fix should be applied (backported) to LTS > versions too. So I targeted it to the 'net' tree, but send it to both > lists to get a feedback. Greg, Jakub, what is the best tree for this > fix? > > --- > drivers/usb/class/cdc-wdm.c | 1 + > 1 file changed, 1 insertion(+) scripts/get_maintainer.pl is pretty clear this goes through the USB tree. I'll queue it up in a few days, thanks, greg k-h