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

[Bean Huo <huobean@gmail.com>]

On Mon, 2021-01-11 at 09:27 +0800, Can Guo wrote:
> > 
> > If accessing sysfs nodes, which triggers a UFS UPIU request to
> > read/write UFS device descriptors during shutdown flow, there is
> > only
> > one issue that sysfs node access failure since UFS device and LINK
> > has
> > been shutdown. Strictly speaking, the failure comes after
> > ufshcd_set_dev_pwr_mode().
> > 
> >     __ufshcd_query_descriptor: opcode 0x01 for idn 0 failed, index
> > 0,
> > err = -11
> 
> You misunderstood it again. You are expecting a simple query cmd
> error.
> But what really matters are NoC issues[1] and OCP[2]. And
> while/after 
> UFS
> shutting down, either of them may happen.
> 
> [1] When a un-clocked register access issue happens, we call it a
> NoC 
> issue,
> meaning you are tring to access a register when clocks are disabled. 
> This
> leads to system CRASH.
> 

OK, let it simple, share this kind of crash log becuase of access sysfs
node in the shutdown flow.


> [2] OCP is over current protection. While UFS shutting down, you may
> have put UFS regulators to LPM. After that, if you are still trying
> to
> talk to UFS, OCP can happen on VCCQ/VCCQ2. This leads to system
> CRASH 
> too.

the same as above, share the crash log.

> 
> > 
> > Since the shutdown is oneway process, this failure is not big
> > issue. If
> > you meant to avoid this failure for unsafe shutdown, I agree with
> > you,
> > But for the race issue, I don't know.
> > 
> 
> Easy for you to say. System crash is a big issue to any SoC vendors
> I 
> belive.
> 

indeed, crash is serious issue, share the log.


Thanks,
Bean


> Can Guo.