linux-kernel - Re: [PATCH v1 5/6] scsi: ufs: Let host_sem cover the entire system suspend/resume

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Date:   Mon, 17 May 2021 11:22:27 +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>,
        Stanley Chu <stanley.chu@...iatek.com>,
        Bean Huo <beanhuo@...ron.com>,
        Jaegeuk Kim <jaegeuk@...nel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 5/6] scsi: ufs: Let host_sem cover the entire system
 suspend/resume

Hi Bart,

On 2021-05-14 11:55, Bart Van Assche wrote:
> On 5/12/21 10:55 PM, Can Guo wrote:
>> UFS error handling now is doing more than just re-probing, but also 
>> sending
>> scsi cmds, e.g., for clearing UACs, and recovering runtime PM error, 
>> which
>> may change runtime status of scsi devices. To protect system 
>> suspend/resume
>> from being disturbed by error handling, move the host_sem from wl pm 
>> ops
>> to ufshcd_suspend_prepare() and ufshcd_resume_complete().
> 
> In ufshcd.h I found the following:
> 
>  * @host_sem: semaphore used to serialize concurrent contexts
> 
> That's the wrong way to use a synchronization object. A synchronization
> object must protect data instead of code. Does host_sem perhaps need to
> be split into multiple synchronization objects?

Thanks for the comments. These contexts are changing critical data and
registers, so the sem is used to protect data actually, just like the
scaling_lock protecting scaling and cmd transations.

Thanks,

Can Guo.

> 
> Thanks,
> 
> Bart.