Re: [PATCH v3] ufs: core: fix lockdep warning of clk_scaling_lock

[Greg KH <gregkh@linuxfoundation.org>]

On Tue, Jul 26, 2022 at 05:14:33PM +0800, peter.wang@mediatek.com wrote:
> From: Peter Wang <peter.wang@mediatek.com>
> 
> There have a lockdep warning like below in current flow.
> kworker/u16:0:  Possible unsafe locking scenario:
> 
> kworker/u16:0:        CPU0                    CPU1
> kworker/u16:0:        ----                    ----
> kworker/u16:0:   lock(&hba->clk_scaling_lock);
> kworker/u16:0:                                lock(&hba->dev_cmd.lock);
> kworker/u16:0:                                lock(&hba->clk_scaling_lock);
> kworker/u16:0:   lock(&hba->dev_cmd.lock);
> kworker/u16:0:
> 
> Before this patch clk_scaling_lock was held in reader mode during the ufshcd_wb_toggle() call.
> With this patch applied clk_scaling_lock is not held while ufshcd_wb_toggle() is called.
> 
> This is safe because ufshcd_wb_toggle will held clk_scaling_lock in reader mode "again" in flow
> ufshcd_wb_toggle -> __ufshcd_wb_toggle -> ufshcd_query_flag_retry -> ufshcd_query_flag ->
> ufshcd_exec_dev_cmd -> down_read(&hba->clk_scaling_lock);
> The protect should enough and make sure clock is not change while send command.
> 
> ufshcd_wb_toggle can protected by hba->clk_scaling.is_allowed to make sure
> ufshcd_devfreq_scale function not run concurrently.
> 
> Fixes: 0e9d4ca43ba8 ("scsi: ufs: Protect some contexts from unexpected clock scaling")
> Signed-off-by: Peter Wang <peter.wang@mediatek.com>
> ---
>  drivers/ufs/core/ufshcd.c | 27 ++++++++++++++++-----------
>  1 file changed, 16 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
> index c7b337480e3e..aa57126fdb49 100644
> --- a/drivers/ufs/core/ufshcd.c
> +++ b/drivers/ufs/core/ufshcd.c
> @@ -272,6 +272,7 @@ static void ufshcd_wb_toggle_flush_during_h8(struct ufs_hba *hba, bool set);
>  static inline void ufshcd_wb_toggle_flush(struct ufs_hba *hba, bool enable);
>  static void ufshcd_hba_vreg_set_lpm(struct ufs_hba *hba);
>  static void ufshcd_hba_vreg_set_hpm(struct ufs_hba *hba);
> +static void ufshcd_clk_scaling_allow(struct ufs_hba *hba, bool allow);
>  
>  static inline void ufshcd_enable_irq(struct ufs_hba *hba)
>  {
> @@ -1249,12 +1250,10 @@ static int ufshcd_clock_scaling_prepare(struct ufs_hba *hba)
>  	return ret;
>  }
>  
> -static void ufshcd_clock_scaling_unprepare(struct ufs_hba *hba, bool writelock)
> +static void ufshcd_clock_scaling_unprepare(struct ufs_hba *hba)
>  {
> -	if (writelock)
> -		up_write(&hba->clk_scaling_lock);
> -	else
> -		up_read(&hba->clk_scaling_lock);
> +	up_write(&hba->clk_scaling_lock);
> +
>  	ufshcd_scsi_unblock_requests(hba);
>  	ufshcd_release(hba);
>  }
> @@ -1271,7 +1270,7 @@ 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;
> +	bool wb_toggle = false;
>  
>  	ret = ufshcd_clock_scaling_prepare(hba);
>  	if (ret)
> @@ -1300,13 +1299,19 @@ static int ufshcd_devfreq_scale(struct ufs_hba *hba, bool scale_up)
>  		}
>  	}
>  
> -	/* Enable Write Booster if we have scaled up else disable it */
> -	downgrade_write(&hba->clk_scaling_lock);
> -	is_writelock = false;
> -	ufshcd_wb_toggle(hba, scale_up);
> +	/* Disable clk_scaling until ufshcd_wb_toggle finish */
> +	hba->clk_scaling.is_allowed = false;
> +	wb_toggle = true;
>  
>  out_unprepare:
> -	ufshcd_clock_scaling_unprepare(hba, is_writelock);
> +	ufshcd_clock_scaling_unprepare(hba);
> +
> +	/* Enable Write Booster if we have scaled up else disable it */
> +	if (wb_toggle) {
> +		ufshcd_wb_toggle(hba, scale_up);
> +		ufshcd_clk_scaling_allow(hba, true);
> +	}
> +
>  	return ret;
>  }
>  
> -- 
> 2.18.0
> 

<formletter>

This is not the correct way to submit patches for inclusion in the
stable kernel tree.  Please read:
    https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.

</formletter>