Re: [PATCH 4/6] usbip: fix stub_dev usbip_sockfd_store() races leading to gpf
From: Shuah Khan <skhan@linuxfoundation.org>
Date: 2021-03-10 00:30:05
Also in:
lkml
On 3/9/21 5:03 PM, Tetsuo Handa wrote:
On 2021/03/10 8:52, Shuah Khan wrote:quoted
On 3/9/21 4:40 PM, Tetsuo Handa wrote:quoted
On 2021/03/10 4:50, Shuah Khan wrote:quoted
On 3/9/21 4:04 AM, Tetsuo Handa wrote:quoted
On 2021/03/09 1:27, Shuah Khan wrote:quoted
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.quoted
event handler queues the events. It shouldn't be blocked by attach and detach. The events could originate for various reasons during the host and vhci operations. I don't like using this lock for attach and detach.
quoted
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. Thank you for letting me know. thanks, -- Shuah