Messages in this thread | | | Subject | Re: [BUG] staging: wfx: possible deadlock in wfx_conf_tx() and wfx_add_interface() | From | Jia-Ju Bai <> | Date | Sat, 5 Feb 2022 16:34:50 +0800 |
| |
On 2022/2/1 19:33, 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.
Hi Hillf,
Thanks for your reply and detailed explanation :)
> > BTW if the unusual wfx init is a real use case then we can add a new helper. > > Mind introducing your toy to LKML? How much time have you been put in it? > Its current status and future works?
Do you mean my static analysis tool that generated the report? In fact, I spent 3-4 months of my part time on implementing this tool, which can detect deadlocks caused by locking cycles and improper waiting/waking operations. This tool still reports some false positives, due to missing some special patterns in the kernel code, such as "init_completion() prior to complete()" in this false bug. Thus, I am improving the tool to reduce false positives now. Any suggestion on deadlock detection or the tool would be appreciated, thanks :)
Best wishes, Jia-Ju Bai
| |