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Date:   Thu, 24 Jun 2021 10:16:12 +0800
From:   Can Guo <cang@codeaurora.org>
To:     Adrian Hunter <adrian.hunter@intel.com>
Cc:     asutoshd@codeaurora.org, nguyenb@codeaurora.org,
        hongwus@codeaurora.org, ziqichen@codeaurora.org,
        linux-scsi@vger.kernel.org, kernel-team@android.com,
        Alim Akhtar <alim.akhtar@samsung.com>,
        Avri Altman <avri.altman@wdc.com>,
        "James E.J. Bottomley" <jejb@linux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        Stanley Chu <stanley.chu@mediatek.com>,
        Bean Huo <beanhuo@micron.com>,
        Jaegeuk Kim <jaegeuk@kernel.org>,
        open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v4 06/10] scsi: ufs: Remove host_sem used in
 suspend/resume
In-Reply-To: <ed59d61a-6951-2acd-4f89-40f8dc5015e1@intel.com>
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 <1624433711-9339-8-git-send-email-cang@codeaurora.org>
 <ed59d61a-6951-2acd-4f89-40f8dc5015e1@intel.com>
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On 2021-06-23 22:30, Adrian Hunter wrote:
> On 23/06/21 10:35 am, Can Guo wrote:
>> To protect system suspend/resume from being disturbed by error 
>> handling,
>> instead of using host_sem, let error handler call lock_system_sleep() 
>> and
>> unlock_system_sleep() which achieve the same purpose. Remove the 
>> host_sem
>> used in suspend/resume paths to make the code more readable.
>> 
>> Suggested-by: Bart Van Assche <bvanassche@acm.org>
>> Signed-off-by: Can Guo <cang@codeaurora.org>
>> ---
>>  drivers/scsi/ufs/ufshcd.c | 12 +++++++-----
>>  1 file changed, 7 insertions(+), 5 deletions(-)
>> 
>> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
>> index 3695dd2..a09e4a2 100644
>> --- a/drivers/scsi/ufs/ufshcd.c
>> +++ b/drivers/scsi/ufs/ufshcd.c
>> @@ -5907,6 +5907,11 @@ static void ufshcd_clk_scaling_suspend(struct 
>> ufs_hba *hba, bool suspend)
>> 
>>  static void ufshcd_err_handling_prepare(struct ufs_hba *hba)
>>  {
>> +	/*
>> +	 * It is not safe to perform error handling while suspend or resume 
>> is
>> +	 * in progress. Hence the lock_system_sleep() call.
>> +	 */
>> +	lock_system_sleep();
> 
> It looks to me like the system takes this lock quite early, even before
> freezing tasks, so if anything needs the error handler to run it will
> deadlock.

Hi Adrian,

UFS/hba system suspend/resume does not invoke or call error handling in 
a
synchronous way. So, whatever UFS errors (which schedules the error 
handler)
happens during suspend/resume, error handler will just wait here till 
system
suspend/resume release the lock. Hence no worries of deadlock here.

Thanks,

Can Guo.

> 
>>  	ufshcd_rpm_get_sync(hba);
>>  	if (pm_runtime_status_suspended(&hba->sdev_ufs_device->sdev_gendev) 
>> ||
>>  	    hba->is_wlu_sys_suspended) {
>> @@ -5951,6 +5956,7 @@ static void ufshcd_err_handling_unprepare(struct 
>> ufs_hba *hba)
>>  		ufshcd_clk_scaling_suspend(hba, false);
>>  	ufshcd_clear_ua_wluns(hba);
>>  	ufshcd_rpm_put(hba);
>> +	unlock_system_sleep();
>>  }
>> 
>>  static inline bool ufshcd_err_handling_should_stop(struct ufs_hba 
>> *hba)
>> @@ -9053,16 +9059,13 @@ static int ufshcd_wl_suspend(struct device 
>> *dev)
>>  	ktime_t start = ktime_get();
>> 
>>  	hba = shost_priv(sdev->host);
>> -	down(&hba->host_sem);
>> 
>>  	if (pm_runtime_suspended(dev))
>>  		goto out;
>> 
>>  	ret = __ufshcd_wl_suspend(hba, UFS_SYSTEM_PM);
>> -	if (ret) {
>> +	if (ret)
>>  		dev_err(&sdev->sdev_gendev, "%s failed: %d\n", __func__,  ret);
>> -		up(&hba->host_sem);
>> -	}
>> 
>>  out:
>>  	if (!ret)
>> @@ -9095,7 +9098,6 @@ static int ufshcd_wl_resume(struct device *dev)
>>  		hba->curr_dev_pwr_mode, hba->uic_link_state);
>>  	if (!ret)
>>  		hba->is_wlu_sys_suspended = false;
>> -	up(&hba->host_sem);
>>  	return ret;
>>  }
>>  #endif
>>