[v2] ufs: core: fix lockdep warning of clk_scaling_lock

Commit Message

Peter Wang (王信友) July 25, 2022, 4:30 a.m. UTC

From: Peter Wang <[e-mail]>

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.

Signed-off-by: Peter Wang <[e-mail]>
---
 drivers/ufs/core/ufshcd.c | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

Comments

Bart Van Assche July 25, 2022, 4:56 p.m. UTC | #1

On 7/24/22 21:30, [e-mail] wrote:
> From: Peter Wang <[e-mail]>
> 
> 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.

Since this is a bug fix, please add a Fixes: tag.

>   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;
>   }

Can the above patch can have the following unwanted effect?
* ufshcd_devfreq_scale() calls ufshcd_clock_scaling_unprepare().
* Clock scaling to a lower frequency happens.
* ufshcd_wb_toggle() enables the write booster.

Shouldn't the above ufshcd_wb_toggle() call be surrounded by down_read() 
and up_read() calls in addition to a check whether the WriteBooster 
really should be enabled instead of using 'scale_up'?

Thanks,

Bart.

Patch

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;
 }