On 01.05.22 19:58, 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") > Signed-off-by: Sergey Ryazanov <ryazanov.s.a@xxxxxxxxx> > Acked-by: Oliver Neukum <oneukum@xxxxxxxx>