pwm: avoid holding mutex in interrupt context

The introduction of the mutex in commit d1cd21427747 ("pwm: Set enable state properly on failed call to enable") effectively makes all PWM drivers potentially sleeping. That in turn makes the .can_sleep field obsolete since all drivers can now sleep.

Changes fix the below bug by using spinlocks instead of mutex

[   22.300239] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:97
[   22.307212] in_atomic(): 1, irqs_disabled(): 0, pid: 2257, name: sh
[   22.313454] Preemption disabled at:[<  (null)>]   (null)
[   23.655232] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:97
[   23.662174] in_atomic(): 1, irqs_disabled(): 0, pid: 2404, name: upowerd
[   23.668932] Preemption disabled at:[<  (null)>]   (null)
[   25.010207] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:97
[   25.017125] in_atomic(): 1, irqs_disabled(): 0, pid: 2262, name: indicator-keybo
[   25.024491] Preemption disabled at:[<  (null)>]   (null)
[   26.355237] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:97
[   26.362141] in_atomic(): 1, irqs_disabled(): 0, pid: 0, name: swapper/0
[   26.368728] Preemption disabled at:[<  (null)>]   (null)
[   27.680220] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:97
[   27.687119] in_atomic(): 1, irqs_disabled(): 0, pid: 0, name: swapper/0
[   27.693698] Preemption disabled at:[<  (null)>]   (null)
[   29.005199] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:97
[   29.012124] in_atomic(): 1, irqs_disabled(): 0, pid: 0, name: swapper/0

[[email protected]: Fixed the commit message]

Signed-off-by Anand Moon <[email protected]>

---
Changes logs: droped my prevoius approch.

---
 drivers/pwm/core.c  | 10 +++++-----
 include/linux/pwm.h |  4 ++--
 2 files changed, 7 insertions(+), 7 deletions(-)

drivers/pwm/core.c +1 -1

index d24ca5f..58e7091 100644
@@ -269,7 +269,7 @@ int pwmchip_add_with_polarity(struct pwm_chip *chip,
 		pwm->pwm = chip->base + i;
 		pwm->hwpwm = i;
 		pwm->polarity = polarity;
-		mutex_init(&pwm->lock);
+		spin_lock_init(&pwm->lock);
 
 		radix_tree_insert(&pwm_tree, pwm->pwm, pwm);
 	}

drivers/pwm/core.c +3 -3

 	if (pwm_is_enabled(pwm)) {
 		err = -EBUSY;

@@ -488,7 +488,7 @@ int pwm_set_polarity(struct pwm_device *pwm, enum pwm_polarity polarity)
 	pwm->polarity = polarity;
 
 unlock:
-	mutex_unlock(&pwm->lock);
+	spin_unlock_irq(&pwm->lock);
 	return err;
 }
 EXPORT_SYMBOL_GPL(pwm_set_polarity);

@@ -506,7 +506,7 @@ int pwm_enable(struct pwm_device *pwm)
 	if (!pwm)
 		return -EINVAL;
 
-	mutex_lock(&pwm->lock);
+	spin_lock_irq(&pwm->lock);
 
 	if (!test_and_set_bit(PWMF_ENABLED, &pwm->flags)) {
 		err = pwm->chip->ops->enable(pwm->chip, pwm);

@@ -514,7 +514,7 @@ int pwm_enable(struct pwm_device *pwm)
 			clear_bit(PWMF_ENABLED, &pwm->flags);
 	}
 
-	mutex_unlock(&pwm->lock);
+	spin_unlock_irq(&pwm->lock);
 
 	return err;
 }

include/linux/pwm.h +2 -2

index cfc3ed4..86ad4c2 100644
@@ -2,7 +2,7 @@
 #define __LINUX_PWM_H
 
 #include <linux/err.h>
-#include <linux/mutex.h>
+#include <linux/spinlock.h>
 #include <linux/of.h>
 
 struct pwm_device;

@@ -100,7 +100,7 @@ struct pwm_device {
 	unsigned int pwm;
 	struct pwm_chip *chip;
 	void *chip_data;
-	struct mutex lock;
+	spinlock_t lock;
 
 	unsigned int period;
 	unsigned int duty_cycle;

Quoted 48 lines · Anand Moon

The introduction of the mutex in commit d1cd21427747 ("pwm: Set enable state properly on failed call to enable") effectively makes all PWM drivers potentially sleeping. That in turn makes the .can_sleep field obsolete since all drivers can now sleep.

Changes fix the below bug by using spinlocks instead of mutex

[   22.300239] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:97
[   22.307212] in_atomic(): 1, irqs_disabled(): 0, pid: 2257, name: sh
[   22.313454] Preemption disabled at:[<  (null)>]   (null)
[   23.655232] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:97
[   23.662174] in_atomic(): 1, irqs_disabled(): 0, pid: 2404, name: upowerd
[   23.668932] Preemption disabled at:[<  (null)>]   (null)
[   25.010207] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:97
[   25.017125] in_atomic(): 1, irqs_disabled(): 0, pid: 2262, name: indicator-keybo
[   25.024491] Preemption disabled at:[<  (null)>]   (null)
[   26.355237] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:97
[   26.362141] in_atomic(): 1, irqs_disabled(): 0, pid: 0, name: swapper/0
[   26.368728] Preemption disabled at:[<  (null)>]   (null)
[   27.680220] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:97
[   27.687119] in_atomic(): 1, irqs_disabled(): 0, pid: 0, name: swapper/0
[   27.693698] Preemption disabled at:[<  (null)>]   (null)
[   29.005199] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:97
[   29.012124] in_atomic(): 1, irqs_disabled(): 0, pid: 0, name: swapper/0

[[email protected]: Fixed the commit message]

Signed-off-by Anand Moon <[email protected]>

---
Changes logs: droped my prevoius approch.

---
 drivers/pwm/core.c  | 10 +++++-----
 include/linux/pwm.h |  4 ++--
 2 files changed, 7 insertions(+), 7 deletions(-)

drivers/pwm/core.c +1 -1

index d24ca5f..58e7091 100644
@@ -269,7 +269,7 @@ int pwmchip_add_with_polarity(struct pwm_chip *chip,
              pwm->pwm = chip->base + i;
              pwm->hwpwm = i;
              pwm->polarity = polarity;
-             mutex_init(&pwm->lock);
+             spin_lock_init(&pwm->lock);
 
              radix_tree_insert(&pwm_tree, pwm->pwm, pwm);
      }

drivers/pwm/core.c int pwm_set_polarity(struct pwm_device *pwm, enum pwm_polarity polarity) · line 477

Quoted 5 lines

drivers/pwm/core.c +1 -1

@@ -474,7 +474,7 @@ int pwm_set_polarity(struct pwm_device *pwm, enum pwm_polarity polarity)
      if (!pwm->chip->ops->set_polarity)
              return -ENOSYS;
 
-     mutex_lock(&pwm->lock);
+     spin_lock_irq(&pwm->lock);

Anand,

Thank you for the effort put into digging into this issue. Unfortunately this approach is bad. You cannot fix one issue without looking at the big picture of the given subsystem. This patch does exactly this - fixes your warning but probably introduces bugs all over the place.

Although the set_polarity callback (called under the lock) is not described as sleeping-allowed but some implementations do it in a sleeping way. This is really easy to find, e.g.:
pwm_omap_dmtimer_set_polarity.

This means: no.

Best regards,
Krzysztof

Quoted 53 lines

drivers/pwm/core.c +3 -3

      if (pwm_is_enabled(pwm)) {
              err = -EBUSY;

@@ -488,7 +488,7 @@ int pwm_set_polarity(struct pwm_device *pwm, enum pwm_polarity polarity)
      pwm->polarity = polarity;
 
 unlock:
-     mutex_unlock(&pwm->lock);
+     spin_unlock_irq(&pwm->lock);
      return err;
 }
 EXPORT_SYMBOL_GPL(pwm_set_polarity);

@@ -506,7 +506,7 @@ int pwm_enable(struct pwm_device *pwm)
      if (!pwm)
              return -EINVAL;
 
-     mutex_lock(&pwm->lock);
+     spin_lock_irq(&pwm->lock);
 
      if (!test_and_set_bit(PWMF_ENABLED, &pwm->flags)) {
              err = pwm->chip->ops->enable(pwm->chip, pwm);

@@ -514,7 +514,7 @@ int pwm_enable(struct pwm_device *pwm)
                      clear_bit(PWMF_ENABLED, &pwm->flags);
      }
 
-     mutex_unlock(&pwm->lock);
+     spin_unlock_irq(&pwm->lock);
 
      return err;
 }

include/linux/pwm.h +2 -2

index cfc3ed4..86ad4c2 100644
@@ -2,7 +2,7 @@
 #define __LINUX_PWM_H
 
 #include <linux/err.h>
-#include <linux/mutex.h>
+#include <linux/spinlock.h>
 #include <linux/of.h>
 
 struct pwm_device;

@@ -100,7 +100,7 @@ struct pwm_device {
      unsigned int pwm;
      struct pwm_chip *chip;
      void *chip_data;
-     struct mutex lock;
+     spinlock_t lock;
 
      unsigned int period;
      unsigned int duty_cycle;

Quoted 48 lines · Anand Moon

The introduction of the mutex in commit d1cd21427747 ("pwm: Set enable state properly on failed call to enable") effectively makes all PWM drivers potentially sleeping. That in turn makes the .can_sleep field obsolete since all drivers can now sleep.

Changes fix the below bug by using spinlocks instead of mutex

[   22.300239] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:97
[   22.307212] in_atomic(): 1, irqs_disabled(): 0, pid: 2257, name: sh
[   22.313454] Preemption disabled at:[<  (null)>]   (null)
[   23.655232] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:97
[   23.662174] in_atomic(): 1, irqs_disabled(): 0, pid: 2404, name: upowerd
[   23.668932] Preemption disabled at:[<  (null)>]   (null)
[   25.010207] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:97
[   25.017125] in_atomic(): 1, irqs_disabled(): 0, pid: 2262, name: indicator-keybo
[   25.024491] Preemption disabled at:[<  (null)>]   (null)
[   26.355237] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:97
[   26.362141] in_atomic(): 1, irqs_disabled(): 0, pid: 0, name: swapper/0
[   26.368728] Preemption disabled at:[<  (null)>]   (null)
[   27.680220] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:97
[   27.687119] in_atomic(): 1, irqs_disabled(): 0, pid: 0, name: swapper/0
[   27.693698] Preemption disabled at:[<  (null)>]   (null)
[   29.005199] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:97
[   29.012124] in_atomic(): 1, irqs_disabled(): 0, pid: 0, name: swapper/0

[[email protected]: Fixed the commit message]

Signed-off-by Anand Moon <[email protected]>

---
Changes logs: droped my prevoius approch.

---
 drivers/pwm/core.c  | 10 +++++-----
 include/linux/pwm.h |  4 ++--
 2 files changed, 7 insertions(+), 7 deletions(-)

drivers/pwm/core.c +1 -1

index d24ca5f..58e7091 100644
@@ -269,7 +269,7 @@ int pwmchip_add_with_polarity(struct pwm_chip *chip,
              pwm->pwm = chip->base + i;
              pwm->hwpwm = i;
              pwm->polarity = polarity;
-             mutex_init(&pwm->lock);
+             spin_lock_init(&pwm->lock);
 
              radix_tree_insert(&pwm_tree, pwm->pwm, pwm);
      }

drivers/pwm/core.c int pwm_set_polarity(struct pwm_device *pwm, enum pwm_polarity polarity) · line 477

Quoted 5 lines

drivers/pwm/core.c +1 -1

@@ -474,7 +474,7 @@ int pwm_set_polarity(struct pwm_device *pwm, enum pwm_polarity polarity)
      if (!pwm->chip->ops->set_polarity)
              return -ENOSYS;
 
-     mutex_lock(&pwm->lock);
+     spin_lock_irq(&pwm->lock);

Anand,

Thank you for the effort put into digging into this issue. Unfortunately this approach is bad. You cannot fix one issue without looking at the big picture of the given subsystem. This patch does exactly this - fixes your warning but probably introduces bugs all over the place.

Although the set_polarity callback (called under the lock) is not described as sleeping-allowed but some implementations do it in a sleeping way. This is really easy to find, e.g.:
pwm_omap_dmtimer_set_polarity.

This means: no.

Best regards,
Krzysztof

Quoted 53 lines

drivers/pwm/core.c +3 -3

      if (pwm_is_enabled(pwm)) {
              err = -EBUSY;

@@ -488,7 +488,7 @@ int pwm_set_polarity(struct pwm_device *pwm, enum pwm_polarity polarity)
      pwm->polarity = polarity;
 
 unlock:
-     mutex_unlock(&pwm->lock);
+     spin_unlock_irq(&pwm->lock);
      return err;
 }
 EXPORT_SYMBOL_GPL(pwm_set_polarity);

@@ -506,7 +506,7 @@ int pwm_enable(struct pwm_device *pwm)
      if (!pwm)
              return -EINVAL;
 
-     mutex_lock(&pwm->lock);
+     spin_lock_irq(&pwm->lock);
 
      if (!test_and_set_bit(PWMF_ENABLED, &pwm->flags)) {
              err = pwm->chip->ops->enable(pwm->chip, pwm);

@@ -514,7 +514,7 @@ int pwm_enable(struct pwm_device *pwm)
                      clear_bit(PWMF_ENABLED, &pwm->flags);
      }
 
-     mutex_unlock(&pwm->lock);
+     spin_unlock_irq(&pwm->lock);
 
      return err;
 }

include/linux/pwm.h +2 -2

index cfc3ed4..86ad4c2 100644
@@ -2,7 +2,7 @@
 #define __LINUX_PWM_H
 
 #include <linux/err.h>
-#include <linux/mutex.h>
+#include <linux/spinlock.h>
 #include <linux/of.h>
 
 struct pwm_device;

@@ -100,7 +100,7 @@ struct pwm_device {
      unsigned int pwm;
      struct pwm_chip *chip;
      void *chip_data;
-     struct mutex lock;
+     spinlock_t lock;
 
      unsigned int period;
      unsigned int duty_cycle;

Hi Krzysztof,

Quoted 67 lines · Krzysztof Kozlowski

Quoted 48 lines · Anand Moon

The introduction of the mutex in commit d1cd21427747 ("pwm: Set enable state properly on failed call to enable") effectively makes all PWM drivers potentially sleeping. That in turn makes the .can_sleep field obsolete since all drivers can now sleep.

Changes fix the below bug by using spinlocks instead of mutex

[   22.300239] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:97
[   22.307212] in_atomic(): 1, irqs_disabled(): 0, pid: 2257, name: sh
[   22.313454] Preemption disabled at:[<  (null)>]   (null)
[   23.655232] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:97
[   23.662174] in_atomic(): 1, irqs_disabled(): 0, pid: 2404, name: upowerd
[   23.668932] Preemption disabled at:[<  (null)>]   (null)
[   25.010207] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:97
[   25.017125] in_atomic(): 1, irqs_disabled(): 0, pid: 2262, name: indicator-keybo
[   25.024491] Preemption disabled at:[<  (null)>]   (null)
[   26.355237] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:97
[   26.362141] in_atomic(): 1, irqs_disabled(): 0, pid: 0, name: swapper/0
[   26.368728] Preemption disabled at:[<  (null)>]   (null)
[   27.680220] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:97
[   27.687119] in_atomic(): 1, irqs_disabled(): 0, pid: 0, name: swapper/0
[   27.693698] Preemption disabled at:[<  (null)>]   (null)
[   29.005199] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:97
[   29.012124] in_atomic(): 1, irqs_disabled(): 0, pid: 0, name: swapper/0

[[email protected]: Fixed the commit message]

Signed-off-by Anand Moon <[email protected]>

---
Changes logs: droped my prevoius approch.

---
 drivers/pwm/core.c  | 10 +++++-----
 include/linux/pwm.h |  4 ++--
 2 files changed, 7 insertions(+), 7 deletions(-)

drivers/pwm/core.c +1 -1

index d24ca5f..58e7091 100644
@@ -269,7 +269,7 @@ int pwmchip_add_with_polarity(struct pwm_chip *chip,
              pwm->pwm = chip->base + i;
              pwm->hwpwm = i;
              pwm->polarity = polarity;
-             mutex_init(&pwm->lock);
+             spin_lock_init(&pwm->lock);
 
              radix_tree_insert(&pwm_tree, pwm->pwm, pwm);
      }

drivers/pwm/core.c int pwm_set_polarity(struct pwm_device *pwm, enum pwm_polarity polarity) · line 477

Quoted 5 lines

drivers/pwm/core.c +1 -1

@@ -474,7 +474,7 @@ int pwm_set_polarity(struct pwm_device *pwm, enum pwm_polarity polarity)
      if (!pwm->chip->ops->set_polarity)
              return -ENOSYS;
 
-     mutex_lock(&pwm->lock);
+     spin_lock_irq(&pwm->lock);

Anand,

Thank you for the effort put into digging into this issue. Unfortunately this approach is bad. You cannot fix one issue without looking at the big picture of the given subsystem. This patch does exactly this - fixes your warning but probably introduces bugs all over the place.

Although the set_polarity callback (called under the lock) is not described as sleeping-allowed but some implementations do it in a sleeping way. This is really easy to find, e.g.:
pwm_omap_dmtimer_set_polarity.

Quoted 5 lines

This means: no.

Best regards,
Krzysztof

Already within function pwm_samsung_set_invert is protected by spin_lock_irqsave(&samsung_pwm_lock, flags);

So no need to introduce another lock to control pwm_samsung_set_polarity.

Best Regards.
-Anand Moon

Quoted 77 lines · Anand Moon

Hi Krzysztof,

Quoted 67 lines · Krzysztof Kozlowski

Quoted 48 lines · Anand Moon

The introduction of the mutex in commit d1cd21427747 ("pwm: Set enable state properly on failed call to enable") effectively makes all PWM drivers potentially sleeping. That in turn makes the .can_sleep field obsolete since all drivers can now sleep.

Changes fix the below bug by using spinlocks instead of mutex

[   22.300239] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:97
[   22.307212] in_atomic(): 1, irqs_disabled(): 0, pid: 2257, name: sh
[   22.313454] Preemption disabled at:[<  (null)>]   (null)
[   23.655232] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:97
[   23.662174] in_atomic(): 1, irqs_disabled(): 0, pid: 2404, name: upowerd
[   23.668932] Preemption disabled at:[<  (null)>]   (null)
[   25.010207] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:97
[   25.017125] in_atomic(): 1, irqs_disabled(): 0, pid: 2262, name: indicator-keybo
[   25.024491] Preemption disabled at:[<  (null)>]   (null)
[   26.355237] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:97
[   26.362141] in_atomic(): 1, irqs_disabled(): 0, pid: 0, name: swapper/0
[   26.368728] Preemption disabled at:[<  (null)>]   (null)
[   27.680220] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:97
[   27.687119] in_atomic(): 1, irqs_disabled(): 0, pid: 0, name: swapper/0
[   27.693698] Preemption disabled at:[<  (null)>]   (null)
[   29.005199] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:97
[   29.012124] in_atomic(): 1, irqs_disabled(): 0, pid: 0, name: swapper/0

[[email protected]: Fixed the commit message]

Signed-off-by Anand Moon <[email protected]>

---
Changes logs: droped my prevoius approch.

---
 drivers/pwm/core.c  | 10 +++++-----
 include/linux/pwm.h |  4 ++--
 2 files changed, 7 insertions(+), 7 deletions(-)

drivers/pwm/core.c +1 -1

index d24ca5f..58e7091 100644
@@ -269,7 +269,7 @@ int pwmchip_add_with_polarity(struct pwm_chip *chip,
              pwm->pwm = chip->base + i;
              pwm->hwpwm = i;
              pwm->polarity = polarity;
-             mutex_init(&pwm->lock);
+             spin_lock_init(&pwm->lock);
 
              radix_tree_insert(&pwm_tree, pwm->pwm, pwm);
      }

drivers/pwm/core.c int pwm_set_polarity(struct pwm_device *pwm, enum pwm_polarity polarity) · line 477

Quoted 5 lines

drivers/pwm/core.c +1 -1

@@ -474,7 +474,7 @@ int pwm_set_polarity(struct pwm_device *pwm, enum pwm_polarity polarity)
      if (!pwm->chip->ops->set_polarity)
              return -ENOSYS;
 
-     mutex_lock(&pwm->lock);
+     spin_lock_irq(&pwm->lock);

Anand,

Thank you for the effort put into digging into this issue. Unfortunately this approach is bad. You cannot fix one issue without looking at the big picture of the given subsystem. This patch does exactly this - fixes your warning but probably introduces bugs all over the place.

Although the set_polarity callback (called under the lock) is not described as sleeping-allowed but some implementations do it in a sleeping way. This is really easy to find, e.g.:
pwm_omap_dmtimer_set_polarity.

Quoted 5 lines

This means: no.

Best regards,
Krzysztof

Quoted 7 lines

Already within function pwm_samsung_set_invert is protected by spin_lock_irqsave(&samsung_pwm_lock, flags);

So no need to introduce another lock to control pwm_samsung_set_polarity.

Best Regards.
-Anand Moon

I don't have any clue what is your point here. I don't get what pwm_samsung_set_polarity has to do with main pwm core...

Sorry, you need to be more specific.

Best regards,
Krzysztof

Hi Krzysztof,

On 18 January 2016 at 09:58, Krzysztof Kozlowski

Quoted 8 lines

Quoted 7 lines

Already within function pwm_samsung_set_invert is protected by spin_lock_irqsave(&samsung_pwm_lock, flags);

So no need to introduce another lock to control pwm_samsung_set_polarity.

Best Regards.
-Anand Moon

Quoted 9 lines

I don't have any clue what is your point here. I don't get what pwm_samsung_set_polarity has to do with main pwm core...

Sorry, you need to be more specific.

Best regards,
Krzysztof

Below is the mapping of calls from pwm driver.
I have tried to map the functionality and I am trying to understand the flow of the driver.

Also looking in document

https://www.kernel.org/doc/Documentation/pwm.txt

pwm-samsung driver controls the LEDS, fans...etc

Form the dts modes pwmleds

        pwmleds {
                compatible = "pwm-leds";

                blueled {
                        label = "blue:heartbeat";
                        pwms = <&pwm 2 2000000 0>;
                        pwm-names = "pwm2";
                        max_brightness = <255>;
                        linux,default-trigger = "heartbeat";
                };
        };

Following is the map out from the device tree.

pwms = <&pwm 2 2000000 0>;

&pwm       ->  pwm: pwm@12dd0000 --->samsung,exynos4210-pwm
2              ->  period
2000000    ->  duty_cycle
0              ->  polarity

And here is the mapping of the call of function
Note: This function call are as per my understanding of the flow in the driver. I might be wrong.

pwm_samsung_set_polarity(struct pwm_chip *chip, struct pwm_device *pwm, enum pwm_polarity polarity)
\
pwm_samsung_set_invert(our_chip, pwm->hwpwm, invert);
\
pwm_set_polarity(struct pwm_device *pwm, enum pwm_polarity polarity)

  \
   pwm->chip->ops->set_polarity(pwm->chip, pwm, polarity);
    \
     pwm_enable(struct pwm_device *pwm) or pwm_disable(struct pwm_device *pwm)

pwm_enable or pwm_disable will be triggered on change in pwm->flags by the pwm core.
before pwm_set_polarity is called form the Samsung driver it hold with following locks

Here is the locking

pwm_samsung_set_polarity(struct pwm_chip *chip, struct pwm_device *pwm, enum pwm_polarity polarity)
\
pwm_samsung_set_invert(struct samsung_pwm_chip *chip, unsigned int
channel, bool invert)

    \
     spin_lock_irqsave(&samsung_pwm_lock, flags);
      \
       pwm_set_polarity(struct pwm_device *pwm, enum pwm_polarity polarity)
       \
        mutex_lock(&pwm->lock)

          pwm_enable(struct pwm_device *pwm) or pwm_disable(struct
pwm_device *pwm)
          \
           mutex_lock(&pwm->lock);

Problem I see that we are holding the lock in interrupt context. I don't know how the this triggers this bug.

BUG: sleeping function called from invalid context at kernel/locking/mutex.c:97

Quoted 45 lines · Anand Moon

Hi Krzysztof,

On 18 January 2016 at 09:58, Krzysztof Kozlowski

Quoted 8 lines

Quoted 7 lines

Already within function pwm_samsung_set_invert is protected by spin_lock_irqsave(&samsung_pwm_lock, flags);

So no need to introduce another lock to control pwm_samsung_set_polarity.

Best Regards.
-Anand Moon

Quoted 9 lines

I don't have any clue what is your point here. I don't get what pwm_samsung_set_polarity has to do with main pwm core...

Sorry, you need to be more specific.

Best regards,
Krzysztof

Below is the mapping of calls from pwm driver.
I have tried to map the functionality and I am trying to understand the flow of the driver.

Also looking in document

https://www.kernel.org/doc/Documentation/pwm.txt

pwm-samsung driver controls the LEDS, fans...etc

Form the dts modes pwmleds

        pwmleds {
                compatible = "pwm-leds";

                blueled {
                        label = "blue:heartbeat";
                        pwms = <&pwm 2 2000000 0>;
                        pwm-names = "pwm2";
                        max_brightness = <255>;
                        linux,default-trigger = "heartbeat";
                };
        };

Quoted 8 lines

Following is the map out from the device tree.

pwms = <&pwm 2 2000000 0>;

&pwm       ->  pwm: pwm@12dd0000 --->samsung,exynos4210-pwm
2              ->  period
2000000    ->  duty_cycle
0              ->  polarity

I do not see any relations between DTS and the problem.

Quoted 11 lines

And here is the mapping of the call of function
Note: This function call are as per my understanding of the flow in the driver. I might be wrong.

pwm_samsung_set_polarity(struct pwm_chip *chip, struct pwm_device *pwm, enum pwm_polarity polarity)
\
pwm_samsung_set_invert(our_chip, pwm->hwpwm, invert);
\
pwm_set_polarity(struct pwm_device *pwm, enum pwm_polarity polarity)

No, pwm_samsung_set_invert does not call pwm_set_polarity(). This would result in a circular call - back to pwm_samsung_set_polarity().

Quoted 32 lines

  \
   pwm->chip->ops->set_polarity(pwm->chip, pwm, polarity);
    \
     pwm_enable(struct pwm_device *pwm) or pwm_disable(struct pwm_device *pwm)

pwm_enable or pwm_disable will be triggered on change in pwm->flags by the pwm core.
before pwm_set_polarity is called form the Samsung driver it hold with following locks

Here is the locking

pwm_samsung_set_polarity(struct pwm_chip *chip, struct pwm_device *pwm, enum pwm_polarity polarity)
\
pwm_samsung_set_invert(struct samsung_pwm_chip *chip, unsigned int
channel, bool invert)

    \
     spin_lock_irqsave(&samsung_pwm_lock, flags);
      \
       pwm_set_polarity(struct pwm_device *pwm, enum pwm_polarity polarity)
       \
        mutex_lock(&pwm->lock)

          pwm_enable(struct pwm_device *pwm) or pwm_disable(struct
pwm_device *pwm)
          \
           mutex_lock(&pwm->lock);

Problem I see that we are holding the lock in interrupt context. I don't know how the this triggers this bug.

Quoted 1 line

BUG: sleeping function called from invalid context at kernel/locking/mutex.c:97

So leave it. If your flow of calls was correct, you would spot the problem. But actually it does not matter - I think the flow is not correct.

Best regards,
Krzysztof

Quoted 45 lines · Anand Moon

Hi Krzysztof,

On 18 January 2016 at 09:58, Krzysztof Kozlowski

Quoted 8 lines

Quoted 7 lines

Already within function pwm_samsung_set_invert is protected by spin_lock_irqsave(&samsung_pwm_lock, flags);

So no need to introduce another lock to control pwm_samsung_set_polarity.

Best Regards.
-Anand Moon

Quoted 9 lines

I don't have any clue what is your point here. I don't get what pwm_samsung_set_polarity has to do with main pwm core...

Sorry, you need to be more specific.

Best regards,
Krzysztof

Below is the mapping of calls from pwm driver.
I have tried to map the functionality and I am trying to understand the flow of the driver.

Also looking in document

https://www.kernel.org/doc/Documentation/pwm.txt

pwm-samsung driver controls the LEDS, fans...etc

Form the dts modes pwmleds

        pwmleds {
                compatible = "pwm-leds";

                blueled {
                        label = "blue:heartbeat";
                        pwms = <&pwm 2 2000000 0>;
                        pwm-names = "pwm2";
                        max_brightness = <255>;
                        linux,default-trigger = "heartbeat";
                };
        };

Quoted 8 lines

Following is the map out from the device tree.

pwms = <&pwm 2 2000000 0>;

&pwm       ->  pwm: pwm@12dd0000 --->samsung,exynos4210-pwm
2              ->  period
2000000    ->  duty_cycle
0              ->  polarity

I do not see any relations between DTS and the problem.

Quoted 11 lines

And here is the mapping of the call of function
Note: This function call are as per my understanding of the flow in the driver. I might be wrong.

pwm_samsung_set_polarity(struct pwm_chip *chip, struct pwm_device *pwm, enum pwm_polarity polarity)
\
pwm_samsung_set_invert(our_chip, pwm->hwpwm, invert);
\
pwm_set_polarity(struct pwm_device *pwm, enum pwm_polarity polarity)

No, pwm_samsung_set_invert does not call pwm_set_polarity(). This would result in a circular call - back to pwm_samsung_set_polarity().

Quoted 29 lines

  \
   pwm->chip->ops->set_polarity(pwm->chip, pwm, polarity);
    \
     pwm_enable(struct pwm_device *pwm) or pwm_disable(struct pwm_device *pwm)

pwm_enable or pwm_disable will be triggered on change in pwm->flags by the pwm core.
before pwm_set_polarity is called form the Samsung driver it hold with following locks

Here is the locking

pwm_samsung_set_polarity(struct pwm_chip *chip, struct pwm_device *pwm, enum pwm_polarity polarity)
\
pwm_samsung_set_invert(struct samsung_pwm_chip *chip, unsigned int
channel, bool invert)

    \
     spin_lock_irqsave(&samsung_pwm_lock, flags);
      \
       pwm_set_polarity(struct pwm_device *pwm, enum pwm_polarity polarity)
       \
        mutex_lock(&pwm->lock)

          pwm_enable(struct pwm_device *pwm) or pwm_disable(struct
pwm_device *pwm)
          \
           mutex_lock(&pwm->lock);

Quoted 4 lines

Problem I see that we are holding the lock in interrupt context. I don't know how the this triggers this bug.

BUG: sleeping function called from invalid context at kernel/locking/mutex.c:97

So leave it. If your flow of calls was correct, you would spot the problem. But actually it does not matter - I think the flow is not correct.

Quoted 101 lines · Krzysztof Kozlowski

Quoted 45 lines · Anand Moon

Hi Krzysztof,

On 18 January 2016 at 09:58, Krzysztof Kozlowski

Quoted 8 lines

Quoted 7 lines

Already within function pwm_samsung_set_invert is protected by spin_lock_irqsave(&samsung_pwm_lock, flags);

So no need to introduce another lock to control pwm_samsung_set_polarity.

Best Regards.
-Anand Moon

Quoted 9 lines

I don't have any clue what is your point here. I don't get what pwm_samsung_set_polarity has to do with main pwm core...

Sorry, you need to be more specific.

Best regards,
Krzysztof

Below is the mapping of calls from pwm driver.
I have tried to map the functionality and I am trying to understand the flow of the driver.

Also looking in document

https://www.kernel.org/doc/Documentation/pwm.txt

pwm-samsung driver controls the LEDS, fans...etc

Form the dts modes pwmleds

        pwmleds {
                compatible = "pwm-leds";

                blueled {
                        label = "blue:heartbeat";
                        pwms = <&pwm 2 2000000 0>;
                        pwm-names = "pwm2";
                        max_brightness = <255>;
                        linux,default-trigger = "heartbeat";
                };
        };

Quoted 8 lines

Following is the map out from the device tree.

pwms = <&pwm 2 2000000 0>;

&pwm       ->  pwm: pwm@12dd0000 --->samsung,exynos4210-pwm
2              ->  period
2000000    ->  duty_cycle
0              ->  polarity

I do not see any relations between DTS and the problem.

Quoted 11 lines

And here is the mapping of the call of function
Note: This function call are as per my understanding of the flow in the driver. I might be wrong.

pwm_samsung_set_polarity(struct pwm_chip *chip, struct pwm_device *pwm, enum pwm_polarity polarity)
\
pwm_samsung_set_invert(our_chip, pwm->hwpwm, invert);
\
pwm_set_polarity(struct pwm_device *pwm, enum pwm_polarity polarity)

No, pwm_samsung_set_invert does not call pwm_set_polarity(). This would result in a circular call - back to pwm_samsung_set_polarity().

Quoted 29 lines

  \
   pwm->chip->ops->set_polarity(pwm->chip, pwm, polarity);
    \
     pwm_enable(struct pwm_device *pwm) or pwm_disable(struct pwm_device *pwm)

pwm_enable or pwm_disable will be triggered on change in pwm->flags by the pwm core.
before pwm_set_polarity is called form the Samsung driver it hold with following locks

Here is the locking

pwm_samsung_set_polarity(struct pwm_chip *chip, struct pwm_device *pwm, enum pwm_polarity polarity)
\
pwm_samsung_set_invert(struct samsung_pwm_chip *chip, unsigned int
channel, bool invert)

    \
     spin_lock_irqsave(&samsung_pwm_lock, flags);
      \
       pwm_set_polarity(struct pwm_device *pwm, enum pwm_polarity polarity)
       \
        mutex_lock(&pwm->lock)

          pwm_enable(struct pwm_device *pwm) or pwm_disable(struct
pwm_device *pwm)
          \
           mutex_lock(&pwm->lock);

Quoted 7 lines

Quoted 4 lines

Problem I see that we are holding the lock in interrupt context. I don't know how the this triggers this bug.

BUG: sleeping function called from invalid context at kernel/locking/mutex.c:97

So leave it. If your flow of calls was correct, you would spot the problem. But actually it does not matter - I think the flow is not correct.

The reason for the BUG that you're seeing is that the leds-pwm driver differentiates between PWMs that can sleep and those that can't. This used to be limited to some PWMs that were attached to a slow bus like I2C, or that called functions which might sleep (like clk_prepare()). With commit d1cd21427747 ("pwm: Set enable state properly on failed call to enable"), effectively all PWM drivers may sleep. The lock introduced in that commit must also be a mutex because it protects sections which may sleep themselves (->enable() and ->set_polarity()) so turning it into a spinlock won't work for the general case.

Given that this is currently broken and we're quite close to -rc1 I suggest the following fix for now:

--- >8 ---

drivers/pwm/core.c +1 -2

index d24ca5f281b4..7831bc6b51dd 100644
@@ -889,7 +889,7 @@ EXPORT_SYMBOL_GPL(devm_pwm_put);
   */
 bool pwm_can_sleep(struct pwm_device *pwm)
 {
-       return pwm->chip->can_sleep;
+       return true;
 }
 EXPORT_SYMBOL_GPL(pwm_can_sleep);
 
--- >8 ---

For v4.6 I can remove all usage of the ->can_sleep and pwm_can_sleep() because they're effectively useless now.

Does that sound reasonable to everyone?

Anand, the above should fix the issue for you. Can you give it a try and report if it doesn't?

Thanks,
Thierry