linux-kernel - Re: [PATCH 2/2] scsi: ufs: Protect PM ops and err

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Date:   Wed, 06 Jan 2021 09:20:44 +0800
From:   Can Guo <cang@...eaurora.org>
To:     Bean Huo <huobean@...il.com>
Cc:     asutoshd@...eaurora.org, nguyenb@...eaurora.org,
        hongwus@...eaurora.org, ziqichen@...eaurora.org,
        rnayak@...eaurora.org, linux-scsi@...r.kernel.org,
        kernel-team@...roid.com, saravanak@...gle.com, salyzyn@...gle.com,
        rjw@...ysocki.net, Alim Akhtar <alim.akhtar@...sung.com>,
        Avri Altman <avri.altman@....com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Stanley Chu <stanley.chu@...iatek.com>,
        Bean Huo <beanhuo@...ron.com>,
        Nitin Rawat <nitirawa@...eaurora.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Bart Van Assche <bvanassche@....org>,
        Satya Tangirala <satyat@...gle.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] scsi: ufs: Protect PM ops and err_handler from user
 access through sysfs

Hi Bean,

On 2021-01-06 02:38, Bean Huo wrote:
> On Tue, 2021-01-05 at 09:07 +0800, Can Guo wrote:
>> On 2021-01-05 04:05, Bean Huo wrote:
>> > On Sat, 2021-01-02 at 05:59 -0800, Can Guo wrote:
>> > > + * @shutting_down: flag to check if shutdown has been invoked
>> >
>> > I am not much sure if this flag is need, since once PM going in
>> > shutdown path, what will be returnded by pm_runtime_get_sync()?
>> >
>> > If pm_runtime_get_sync() will fail, just check its return.
>> >
>> 
>> That depends. During/after shutdown, for UFS's case only,
>> pm_runtime_get_sync(hba->dev) will most likely return 0,
>> because it is already RUNTIME_ACTIVE, pm_runtime_get_sync()
>> will directly return 0... meaning you cannot count on it.
>> 
>> Check Stanley's change -
>> https://lore.kernel.org/patchwork/patch/1341389/
>> 
>> Can Guo.
> 
> Can,
> 
> Thanks for pointing out that.
> 
> Based on my understanding, that patch is redundent. maybe I
> misundestood Linux shutdown sequence.

Sorry, do you mean Stanley's change is redundant?

> 
> I checked the shutdown flow:
> 
> 1. Set the "system_state" variable
> 2. Disable usermod to ensure that no user from userspace can start a
> request

I hope it is like what you interpreted, but step #2 only stops UMH(#265)
but not all user space activities. Whereas, UMH is for kernel space 
calling
user space.

264 	system_state = state;
265 	usermodehelper_disable();
266 	device_shutdown();

Thanks,
Can Guo.

> 3. device_shutdown()
> So, userspace thread can not start a request to trigger runtime
> resume(pm_runtime_get_sync) after step 2.
> 
> also,  no need to add that flag to checkup if shutdwon is running,
> maybe it is better to check variable system_state:
> 
> if (system_state == SYSTEM_POWER_OFF || system_state == SYSTEM_HALT
> || system_state == SYSTEM_RESTART)
> 	//shutdown start
> 
> 
> I still hope Rafael or someone else can confirm that if
> pm_runtime_get_sync() will really return ok in shutdown flow.
> 
> 
> thanks,
> Bean
> 
>> 
>> > Hi Rafael
>> > would you please help us confirm this?
>> >
>> > thanks,
>> > Bean