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ufs: core: fix lockdep warning of clk_scaling_lock

PATCH Superseded [email protected] 2 participants 3 messages Jul 26, 2022 – Jul 27, 2022

Subsystems (4)
Stable branch SCSI Arm MediaTek UFS host controller

v3 of 4 Superseded Latest is v4 →

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#0 lore raw

PATCH v3 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:

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 <[email protected]>
---
 drivers/ufs/core/ufshcd.c | 27 ++++++++++++++++-----------
 1 file changed, 16 insertions(+), 11 deletions(-)
drivers/ufs/core/ufshcd.c +16 -11
index c7b337480e3e..aa57126fdb49 100644
@@ -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;
 }
Signature · 1 line
2.18.0
maintainer
#1 lore raw
Quoted 95 lines · On Tue, Jul 26, 2022 at 05:14:33PM +0800, [email protected] wrote:

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:

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 <[email protected]>
---
 drivers/ufs/core/ufshcd.c | 27 ++++++++++++++++-----------
 1 file changed, 16 insertions(+), 11 deletions(-)
drivers/ufs/core/ufshcd.c +16 -11
index c7b337480e3e..aa57126fdb49 100644
@@ -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;
 }
Signature · 1 line
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>

author
#2 lore raw
Quoted 98 lines · Greg KH
Quoted 95 lines · On Tue, Jul 26, 2022 at 05:14:33PM +0800, [email protected] wrote:

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:

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 <[email protected]>
---
  drivers/ufs/core/ufshcd.c | 27 ++++++++++++++++-----------
  1 file changed, 16 insertions(+), 11 deletions(-)
drivers/ufs/core/ufshcd.c +16 -11
index c7b337480e3e..aa57126fdb49 100644
@@ -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;
  }
Signature · 1 line
2.18.0

<formletter>

Quoted 4 lines

This is not the correct way to submit patches for inclusion in the stable kernel tree. Please read:
https://urldefense.com/v3/__https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html__;!!CTRNKA9wMg0ARbw!24V8xNPFu0-WdpS3FH6jpUbnVGjhGphz8M0EYnzuRQWgnNx5qPBSLSwEtdHFyz63fw$
for how to do this properly.

Hi Greg,

Thank you for remind.

Will use correct way next version

Thanks

Peter

Quoted 2 lines

</formletter>