linux-kernel - Re: [PATCH v2 05/12] usb: otg-fsm: Fix hrtimer list corruption

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Date:   Mon, 5 Jul 2021 05:45:08 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Peter Chen <peter.chen@...nel.org>
Cc:     Thierry Reding <treding@...dia.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Mark Brown <broonie@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Sebastian Reichel <sre@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Felipe Balbi <balbi@...nel.org>,
        David Heidelberg <david@...t.cz>, devicetree@...r.kernel.org,
        linux-pm@...r.kernel.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-tegra@...r.kernel.org
Subject: Re: [PATCH v2 05/12] usb: otg-fsm: Fix hrtimer list corruption

05.07.2021 05:21, Peter Chen пишет:
> On 21-07-03 20:22:38, Dmitry Osipenko wrote:
>> 03.07.2021 14:08, Peter Chen пишет:
>>> On 21-07-02 02:43:10, Dmitry Osipenko wrote:
>>>> The HNP work can be re-scheduled while it's still in-fly. This results in
>>>> re-initialization of the busy work, resetting the hrtimer's list node of
>>>> the work and crashing kernel with null dereference within kernel/timer
>>>> once work's timer is expired. It's very easy to trigger this problem by
>>>> re-plugging USB cable quickly. Initialize HNP work only once to fix this
>>>> trouble.
>>>
>>> Fully OTG compliance support has not maintained for years, what's the use case you
>>> still want to use?
>>
>> I don't have any use case for it, but I had CONFIG_USB_OTG_FSM=y and it
>> was crashing kernel badly. The OTG works perfectly fine without the FSM.
> 
> You could add below at your dts to disable OTG FSM:
> hnp-disable
> srp-disable
> adp-disable
> 
> Since there are no users for OTG FSM, it hasn't maintained for years,
> I am not sure if it still works OK. If I remember correctly, the VBUS
> will be off if you enable HNP, and the device at the host port will be
> disconnected, that's may not your expectation.
> 

Since OTG FSM is known to be in a bad shape, could you please make a
patch to remove it? I hope it's not enabled by default in a distro
kernels.. oh no, CONFIG_USB_OTG_FSM=y at least in ArchLinux [1].

[1] https://archlinuxarm.org/packages/armv7h/linux-armv7/files/config

I think we should fix that hrtimer bug, beackport the fix into stable
kernels and then remove OTG FSM. Does this sound good to you?