[PATCH v1] ufs: core: fix lockdep warning of clk_scaling_lock

[PATCH v1] ufs: core: fix lockdep warning of clk_scaling_lock

[peter.wang]

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:

Because ufshcd_wb_toggle -> ufshcd_query_flag -> ufshcd_exec_dev_cmd
will get read lock of clk_scaling_lock, so ufshcd_devfreq_scale
can release read lock before call ufshcd_wb_toggle.
This patch only release write lock of clk_scaling_lock before
ufshcd_wb_toggle.

---
 drivers/ufs/core/ufshcd.c | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
index c7b337480e3e..209089bd8085 100644
--- a/drivers/ufs/core/ufshcd.c
+++ b/drivers/ufs/core/ufshcd.c
@@ -1249,12 +1249,10 @@ 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 +1269,7 @@ 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 +1298,15 @@ 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);
+	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);
+
 	return ret;
 }
 
-- 
2.18.0

Re: [PATCH v1] ufs: core: fix lockdep warning of clk_scaling_lock

[Bart Van Assche]

On 7/22/22 02:53, peter.wang@mediatek.com wrote:
> This patch only release write lock of clk_scaling_lock before
> ufshcd_wb_toggle.

The above is not clear to me. Please make the above more clear.

Additionally, patches must be signed before these can be merged 
upstream. Where is your Signed-off-by?

> -	/* 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);
> +	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);
> +
>   	return ret;
>   }

The patch description should mention that this patch changes the 
ufshcd_wb_toggle() call: before this patch clk_scaling_lock was held in 
reader mode during the ufshcd_wb_toggle() call and with this patch 
applied clk_scaling_lock is not held while ufshcd_wb_toggle() is called. 
I'm missing an explanation of why this change is safe.

Thanks,

Bart.

Re: [PATCH v1] ufs: core: fix lockdep warning of clk_scaling_lock

[Peter Wang]

On 7/23/22 5:00 AM, Bart Van Assche wrote:
> On 7/22/22 02:53, peter.wang@mediatek.com wrote:
>> This patch only release write lock of clk_scaling_lock before
>> ufshcd_wb_toggle.
>
> The above is not clear to me. Please make the above more clear.
>
> Additionally, patches must be signed before these can be merged 
> upstream. Where is your Signed-off-by?
>
>> -    /* 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);
>> +    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);
>> +
>>       return ret;
>>   }
>
> The patch description should mention that this patch changes the 
> ufshcd_wb_toggle() call: before this patch clk_scaling_lock was held 
> in reader mode during the ufshcd_wb_toggle() call and with this patch 
> applied clk_scaling_lock is not held while ufshcd_wb_toggle() is 
> called. I'm missing an explanation of why this change is safe.
>
> Thanks,
>
> Bart.
>

Hi Bart,

okay, I will make this path more clear and add Signed-off-by
Thanks for review.

Peter