linux-kernel - Re: [PATCH 4/6] usbip: fix stub_dev usbip_sockfd

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Message-ID: <f8f5e763-da2d-b26f-c6a5-d345bbe55448@i-love.sakura.ne.jp>
Date:   Tue, 9 Mar 2021 20:04:52 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Shuah Khan <skhan@...uxfoundation.org>, shuah@...nel.org,
        valentina.manea.m@...il.com, gregkh@...uxfoundation.org
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/6] usbip: fix stub_dev usbip_sockfd_store() races
 leading to gpf

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.