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Subject: Re: [PATCH v4 06/10] scsi: ufs: Remove host_sem used in
 suspend/resume
To:     Can Guo <cang@codeaurora.org>, asutoshd@codeaurora.org,
        nguyenb@codeaurora.org, hongwus@codeaurora.org,
        ziqichen@codeaurora.org, linux-scsi@vger.kernel.org,
        kernel-team@android.com
Cc:     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>
References: <1624433711-9339-1-git-send-email-cang@codeaurora.org>
 <1624433711-9339-8-git-send-email-cang@codeaurora.org>
From:   Adrian Hunter <adrian.hunter@intel.com>
Organization: Intel Finland Oy, Registered Address: PL 281, 00181 Helsinki,
 Business Identity Code: 0357606 - 4, Domiciled in Helsinki
Message-ID: <ed59d61a-6951-2acd-4f89-40f8dc5015e1@intel.com>
Date:   Wed, 23 Jun 2021 17:30:38 +0300
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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.

>  	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
>