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

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Date:   Mon, 11 Jan 2021 09:23:35 +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 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.