Hello, On Tuesday 1 February 2022 12:33:03 CET Hillf Danton wrote: > On Tue, 1 Feb 2022 15:09:34 +0800 Jia-Ju Bai wrote: > > Hello, > > > > My static analysis tool reports a possible deadlock in the wfx driver in > > Linux 5.16: > > > > wfx_conf_tx() > > mutex_lock(&wdev->conf_mutex); --> Line 225 (Lock A) > > wfx_update_pm() > > wait_for_completion_timeout(&wvif->set_pm_mode_complete, ...); --> > > Line 3019 (Wait X) > > > > wfx_add_interface() > > mutex_lock(&wdev->conf_mutex); --> Line 737 (Lock A) > > complete(&wvif->set_pm_mode_complete); --> Line 758 (Wake X) > > > > When wfx_conf_tx() is executed, "Wait X" is performed by holding "Lock > > A". If wfx_add_interface() is executed at this time, "Wake X" cannot be > > performed to wake up "Wait X" in wfx_conf_tx(), because "Lock A" has > > been already hold by wfx_conf_tx(), causing a possible deadlock. > > I find that "Wait X" is performed with a timeout, to relieve the > > possible deadlock; but I think this timeout can cause inefficient execution. > > > > I am not quite sure whether this possible problem is real and how to fix > > it if it is real. > > Any feedback would be appreciated, thanks :) > > > > > > Best wishes, > > Jia-Ju Bai > > Hey Jia-Ju > > Thank you for reporting it. > > Given the init_completion() prior to complete() in wfx_add_interface(), > no waiter is waken up by the complete(), so it has nothing to do with > the waiter in the conf path. Absolutely. The completion is done by wfx_hif_pm_mode_complete_indication() (which is not behind a mutex). > BTW if the unusual wfx init is a real use case then we can add a new helper. Indeed, it could make the code better. I don't know if there would be other users. -- Jérôme Pouiller
