linux-kernel - Re: [PATCH v4 10/10] scsi: ufs: Apply more limitations to user access

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Date:   Thu, 24 Jun 2021 10:23:01 +0800
From:   Can Guo <cang@...eaurora.org>
To:     Bart Van Assche <bvanassche@....org>
Cc:     asutoshd@...eaurora.org, nguyenb@...eaurora.org,
        hongwus@...eaurora.org, ziqichen@...eaurora.org,
        linux-scsi@...r.kernel.org, kernel-team@...roid.com,
        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>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Bean Huo <beanhuo@...ron.com>,
        Stanley Chu <stanley.chu@...iatek.com>,
        Keoseong Park <keosung.park@...sung.com>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Jaegeuk Kim <jaegeuk@...nel.org>,
        Kiwoong Kim <kwmad.kim@...sung.com>,
        Satya Tangirala <satyat@...gle.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 10/10] scsi: ufs: Apply more limitations to user access

Hi Bart,

On 2021-06-24 05:51, Bart Van Assche wrote:
> On 6/23/21 12:35 AM, Can Guo wrote:
>> +int ufshcd_get_user_access(struct ufs_hba *hba)
>> +__acquires(&hba->host_sem)
>> +{
>> +	down(&hba->host_sem);
>> +	if (!ufshcd_is_user_access_allowed(hba)) {
>> +		up(&hba->host_sem);
>> +		return -EBUSY;
>> +	}
>> +	if (ufshcd_rpm_get_sync(hba)) {
>> +		ufshcd_rpm_put_sync(hba);
>> +		up(&hba->host_sem);
>> +		return -EBUSY;
>> +	}
>> +	return 0;
>> +}
>> +EXPORT_SYMBOL_GPL(ufshcd_get_user_access);
>> +
>> +void ufshcd_put_user_access(struct ufs_hba *hba)
>> +__releases(&hba->host_sem)
>> +{
>> +	ufshcd_rpm_put_sync(hba);
>> +	up(&hba->host_sem);
>> +}
>> +EXPORT_SYMBOL_GPL(ufshcd_put_user_access);
> 
> Please indent __acquires() and __releases() annotations by one tab as 
> is
> done elsewhere in the kernel.

OK.

> 
>>  static inline bool ufshcd_is_user_access_allowed(struct ufs_hba *hba)
>>  {
>> -	return !hba->shutting_down;
>> +	return !hba->shutting_down && !hba->is_sys_suspended &&
>> +		!hba->is_wlu_sys_suspended &&
>> +		hba->ufshcd_state == UFSHCD_STATE_OPERATIONAL;
>>  }
> 
> Is my understanding of the following correct?
> - ufshcd_is_user_access_allowed() is not in the hot path and hence
>   should not be inline.

OK.

> - The hba->shutting_down member variable is set from inside a shutdown
>   callback. Hence, the hba->shutting_down test can be left out since
>   no UFS sysfs attributes are accessed after shutdown has started.

We see that user can still access UFS sysfs during shutdown if shutdown
is invoked by: reboot -f, hence the check.

> - During system suspend, user space software is paused before the 
> device
>   driver freeze callbacks are invoked. Hence, the hba->is_sys_suspended
>   check can be left out.

is_sys_suspended indicates that system resume failed (power/clk is OFF).

> - If a LUN is runtime suspended, it should be resumed if accessed from
>   user space instead of failing user space accesses. In other words, 
> the
>   hba->is_wlu_sys_suspended check seems inappropriate to me.

hba->is_wlu_sys_suspended indicates that wl system resume failed, device
is not operational.

> - If the HBA is not in an operational state, user space accesses
>   should be blocked until error handling has finished. After error
>   handling has finished, the user space access should fail if and only
>   if error handling failed.
> 

Yes, which is why ufshcd_get_user_access() acquires host_sem first and
checks the OPERATOINAL flag here. host_sem shall make sure that user
space accesses should be blocked until error handling has finished.

Thanks,

Can Guo.

> Thanks,
> 
> Bart.