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

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Date:   Tue, 05 Jan 2021 19:38:26 +0100
From:   Bean Huo <huobean@...il.com>
To:     Can Guo <cang@...eaurora.org>
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

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.

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
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