linux-kernel - Re: [PATCH v3 1/5] scsi: ufs: atomic update for clkgating

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Date:   Mon, 26 Oct 2020 11:28:27 +0800
From:   Can Guo <cang@...eaurora.org>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net, kernel-team@...roid.com,
        alim.akhtar@...sung.com, avri.altman@....com, bvanassche@....org,
        Jaegeuk Kim <jaegeuk@...gle.com>
Subject: Re: [PATCH v3 1/5] scsi: ufs: atomic update for clkgating_enable

On 2020-10-24 23:06, Jaegeuk Kim wrote:
> From: Jaegeuk Kim <jaegeuk@...gle.com>
> 
> When giving a stress test which enables/disables clkgating, we hit 
> device
> timeout sometimes. This patch avoids subtle racy condition to address 
> it.
> 
> If we use __ufshcd_release(), I've seen that gate_work can be called in 
> parallel
> with ungate_work, which results in UFS timeout when doing hibern8.
> Should avoid it.
> 

I don't understand this comment. gate_work and ungate_work are queued on
an ordered workqueue and an ordered workqueue executes at most one work 
item
at any given time in the queued order. How can the two run in parallel?

Thanks,

Can Guo.

> Signed-off-by: Jaegeuk Kim <jaegeuk@...gle.com>
> ---
>  drivers/scsi/ufs/ufshcd.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
> index b8f573a02713..e0b479f9eb8a 100644
> --- a/drivers/scsi/ufs/ufshcd.c
> +++ b/drivers/scsi/ufs/ufshcd.c
> @@ -1807,19 +1807,19 @@ static ssize_t
> ufshcd_clkgate_enable_store(struct device *dev,
>  		return -EINVAL;
> 
>  	value = !!value;
> +
> +	spin_lock_irqsave(hba->host->host_lock, flags);
>  	if (value == hba->clk_gating.is_enabled)
>  		goto out;
> 
> -	if (value) {
> -		ufshcd_release(hba);
> -	} else {
> -		spin_lock_irqsave(hba->host->host_lock, flags);
> +	if (value)
> +		hba->clk_gating.active_reqs--;
> +	else
>  		hba->clk_gating.active_reqs++;
> -		spin_unlock_irqrestore(hba->host->host_lock, flags);
> -	}
> 
>  	hba->clk_gating.is_enabled = value;
>  out:
> +	spin_unlock_irqrestore(hba->host->host_lock, flags);
>  	return count;
>  }