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

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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



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