Re: [PATCH 2/2] scsi: ufs: Protect PM ops and err_handler from user access through sysfs

[Can Guo]

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