On Sun, May 1, 2022 at 9:09 PM Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > 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. Ouch. Sorry. >> 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, Thank you for your clarification, will keep in mind. -- Sergey