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Message-ID: <1514403adf486ac8069253c09f45b021bad32e00.camel@gmail.com>
Subject: Re: [PATCH 2/2] scsi: ufs: Protect PM ops and err_handler from user
 access through sysfs
From:   Bean Huo <huobean@gmail.com>
To:     Can Guo <cang@codeaurora.org>
Cc:     asutoshd@codeaurora.org, nguyenb@codeaurora.org,
        hongwus@codeaurora.org, ziqichen@codeaurora.org,
        rnayak@codeaurora.org, linux-scsi@vger.kernel.org,
        kernel-team@android.com, saravanak@google.com, salyzyn@google.com,
        rjw@rjwysocki.net, Alim Akhtar <alim.akhtar@samsung.com>,
        Avri Altman <avri.altman@wdc.com>,
        "James E.J. Bottomley" <jejb@linux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        Stanley Chu <stanley.chu@mediatek.com>,
        Bean Huo <beanhuo@micron.com>,
        Nitin Rawat <nitirawa@codeaurora.org>,
        Adrian Hunter <adrian.hunter@intel.com>,
        Bart Van Assche <bvanassche@acm.org>,
        Satya Tangirala <satyat@google.com>,
        open list <linux-kernel@vger.kernel.org>
Date:   Tue, 05 Jan 2021 19:38:26 +0100
In-Reply-To: <7d49c1dfc3f648c484076f3c3a7f4e1e@codeaurora.org>
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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