ufs: core: fix lockdep warning of clk_scaling_lock

PATCH Superseded [email protected] 2 participants 3 messages Jul 22, 2022 – Jul 25, 2022

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SCSI Arm MediaTek UFS host controller

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[email protected]

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2022-07-22 09:53 UTC #0 lore raw

PATCH 1/1 ufs: core: fix lockdep warning of clk_scaling_lock

From: Peter Wang <[email protected]>

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(-)

drivers/ufs/core/ufshcd.c +11 ~~-11~~

index c7b337480e3e..209089bd8085 100644
@@ -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;
 }

Signature · 1 line

2.18.0

Bart Van Assche

reviewer

2022-07-22 21:00 UTC #1 lore raw

Quoted 2 lines · On 7/22/22 02:53, [email protected] 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?

Quoted 6 lines

drivers/ufs/core/ufshcd.c +1 -4

-	/* 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;

drivers/ufs/core/ufshcd.c static int ufshcd_devfreq_scale(struct ufs_hba *hba, bool scale_up) · line 1311

Quoted 10 lines

drivers/ufs/core/ufshcd.c +6 -1

  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.

Peter Wang

author

2022-07-25 03:56 UTC #2 lore raw

Quoted 26 lines · Bart Van Assche

Quoted 2 lines · On 7/22/22 02:53, [email protected] 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?
Quoted 13 lines
-    /* 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);
drivers/ufs/core/ufshcd.c +5 -0
+
+    /* Enable Write Booster if we have scaled up else disable it */
+    if (wb_toggle)
+        ufshcd_wb_toggle(hba, scale_up);
+
Quoted 2 lines
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.

Quoted 4 lines

Thanks,
Bart.

Hi Bart,

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

Peter