linux-kernel - Re: [PATCH] scsi: ufs: core: fix devfreq deadlocks

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Date:   Thu, 5 Jan 2023 10:38:58 -0800
From:   Bart Van Assche <bvanassche@....org>
To:     Johan Hovold <johan+linaro@...nel.org>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>
Cc:     Alim Akhtar <alim.akhtar@...sung.com>,
        Avri Altman <avri.altman@....com>, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Can Guo <quic_cang@...cinc.com>
Subject: Re: [PATCH] scsi: ufs: core: fix devfreq deadlocks

On 12/22/22 02:21, Johan Hovold wrote:
> diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
> index bda61be5f035..5c3821b2fcf8 100644
> --- a/drivers/ufs/core/ufshcd.c
> +++ b/drivers/ufs/core/ufshcd.c
> @@ -1234,12 +1234,14 @@ static int ufshcd_clock_scaling_prepare(struct ufs_hba *hba)
>   	 * clock scaling is in progress
>   	 */
>   	ufshcd_scsi_block_requests(hba);
> +	mutex_lock(&hba->wb_mutex);
>   	down_write(&hba->clk_scaling_lock);
>   
>   	if (!hba->clk_scaling.is_allowed ||
>   	    ufshcd_wait_for_doorbell_clr(hba, DOORBELL_CLR_TOUT_US)) {
>   		ret = -EBUSY;
>   		up_write(&hba->clk_scaling_lock);
> +		mutex_unlock(&hba->wb_mutex);
>   		ufshcd_scsi_unblock_requests(hba);
>   		goto out;
>   	}
> @@ -1251,12 +1253,16 @@ static int ufshcd_clock_scaling_prepare(struct ufs_hba *hba)
>   	return ret;
>   }

Please add an __acquires(&hba->wb_mutex) annotation for sparse.

> -static void ufshcd_clock_scaling_unprepare(struct ufs_hba *hba, bool writelock)
> +static void ufshcd_clock_scaling_unprepare(struct ufs_hba *hba, bool scale_up)
>   {
> -	if (writelock)
> -		up_write(&hba->clk_scaling_lock);
> -	else
> -		up_read(&hba->clk_scaling_lock);
> +	up_write(&hba->clk_scaling_lock);
> +
> +	/* Enable Write Booster if we have scaled up else disable it */
> +	if (ufshcd_enable_wb_if_scaling_up(hba))
> +		ufshcd_wb_toggle(hba, scale_up);
> +
> +	mutex_unlock(&hba->wb_mutex);
> +
>   	ufshcd_scsi_unblock_requests(hba);
>   	ufshcd_release(hba);
>   }

Please add a __releases(&hba->wb_mutex) annotation for sparse.

> @@ -1273,7 +1279,6 @@ static void ufshcd_clock_scaling_unprepare(struct ufs_hba *hba, bool writelock)
>   static int ufshcd_devfreq_scale(struct ufs_hba *hba, bool scale_up)
>   {
>   	int ret = 0;
> -	bool is_writelock = true;
>   
>   	ret = ufshcd_clock_scaling_prepare(hba);
>   	if (ret)
> @@ -1302,15 +1307,8 @@ static int ufshcd_devfreq_scale(struct ufs_hba *hba, bool scale_up)
>   		}
>   	}
>   
> -	/* Enable Write Booster if we have scaled up else disable it */
> -	if (ufshcd_enable_wb_if_scaling_up(hba)) {
> -		downgrade_write(&hba->clk_scaling_lock);
> -		is_writelock = false;
> -		ufshcd_wb_toggle(hba, scale_up);
> -	}
> -
>   out_unprepare:
> -	ufshcd_clock_scaling_unprepare(hba, is_writelock);
> +	ufshcd_clock_scaling_unprepare(hba, scale_up);
>   	return ret;
>   }

This patch moves the ufshcd_wb_toggle() from before the out_unprepare 
label to after the out_unprepare label (into 
ufshcd_clock_scaling_unprepare()). Does this change perhaps introduce a 
new call to ufshcd_wb_toggle() in error paths?

Thanks,

Bart.