On 2021/03/10 8:52, Shuah Khan wrote: > On 3/9/21 4:40 PM, Tetsuo Handa wrote: >> On 2021/03/10 4:50, Shuah Khan wrote: >>> On 3/9/21 4:04 AM, Tetsuo Handa wrote: >>>> On 2021/03/09 1:27, Shuah Khan wrote: >>>>> Yes. We might need synchronization between events, threads, and shutdown >>>>> in usbip_host side and in connection polling and threads in vhci. >>>>> >>>>> I am also looking at the shutdown sequences closely as well since the >>>>> local state is referenced without usbip_device lock in these paths. >>>>> >>>>> I am approaching these problems as peeling the onion an expression so >>>>> we can limit the changes and take a spot fix approach. We have the >>>>> goal to address these crashes and not introduce regressions. >>>> >>>> I think my [PATCH v4 01/12]-[PATCH v4 06/12] simplify your further changes >>>> without introducing regressions. While ud->lock is held when checking >>>> ud->status, >>>> current attach/detach code is racy about read/update of ud->status . I >>>> think we >>>> can close race in attach/detach code via a simple usbip_event_mutex >>>> serialization. >>>> >>> >>> Do you mean patches 1,2,3,3,4,5,6? >> >> Yes, my 1,2,3,4,5,6. >> >> Since you think that usbip_prepare_threads() does not worth introducing, I'm >> fine with >> replacing my 7,8,9,10,11,12 with your "[PATCH 0/6] usbip fixes to crashes >> found by syzbot". >> > > Using event lock isn't the right approach to solve the race. It is a > large grain lock. I am not looking to replace patches.
It is not a large grain lock. Since event_handler() is exclusively executed, this lock does _NOT_ block event_handler() unless attach/detach operations run concurrently. > > I still haven't seen any response from you about if you were able to > verify the fixes I sent in fix the problem you are seeing. I won't be able to verify your fixes, for it is syzbot who is seeing the problem. But I can see that your patch description is wrong because you are ignoring what I'm commenting. Global serialization had better come first. Your patch description depends on global serialization.
