[PATCH] gpio: omap: use raw locks for locking

[PATCH] gpio: omap: use raw locks for locking

[Sebastian Andrzej Siewior]

This patch converts gpio_bank.lock from a spin_lock into a
raw_spin_lock. The call path to access this lock is always under a
raw_spin_lock, for instance
- __setup_irq() holds &desc->lock with irq off
  + __irq_set_trigger()
   + omap_gpio_irq_type()

- handle_level_irq() (runs with irqs off therefore raw locks)
  + mask_ack_irq()
   + omap_gpio_mask_irq()

This fixes the obvious backtrace on -RT. However I noticed two cases
where it looks wrong and this is not limited to -RT:
- omap_gpio_irq_type() is called with IRQ off and has an conditional
  call to pm_runtime_get_sync() which may sleep. Either it may happen or
  it may not happen but pm_runtime_get_sync() should not be called in an
  atomic section.

- omap_gpio_debounce() is holding the lock with IRQs off.
  + omap2_set_gpio_debounce()
   + clk_prepare_enable()
    + clk_prepare() this one might sleep.
  The number of users of gpiod_set_debounce() / gpio_set_debounce()
  looks low but still this is not good.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 drivers/gpio/gpio-omap.c | 78 ++++++++++++++++++++++++------------------------
 1 file changed, 39 insertions(+), 39 deletions(-)

diff --git a/drivers/gpio/gpio-omap.c b/drivers/gpio/gpio-omap.c
index f476ae2eb0b3..27e835f4c39d 100644
--- a/drivers/gpio/gpio-omap.c
+++ b/drivers/gpio/gpio-omap.c
@@ -57,7 +57,7 @@ struct gpio_bank {
 	u32 saved_datain;
 	u32 level_mask;
 	u32 toggle_mask;
-	spinlock_t lock;
+	raw_spinlock_t lock;
 	struct gpio_chip chip;
 	struct clk *dbck;
 	u32 mod_usage;
@@ -515,15 +515,15 @@ static int omap_gpio_irq_type(struct irq_data *d, unsigned type)
 		(type & (IRQ_TYPE_LEVEL_LOW|IRQ_TYPE_LEVEL_HIGH)))
 		return -EINVAL;
 
-	spin_lock_irqsave(&bank->lock, flags);
+	raw_spin_lock_irqsave(&bank->lock, flags);
 	offset = GPIO_INDEX(bank, gpio);
 	retval = omap_set_gpio_triggering(bank, offset, type);
 	omap_gpio_init_irq(bank, gpio, offset);
 	if (!omap_gpio_is_input(bank, BIT(offset))) {
-		spin_unlock_irqrestore(&bank->lock, flags);
+		raw_spin_unlock_irqrestore(&bank->lock, flags);
 		return -EINVAL;
 	}
-	spin_unlock_irqrestore(&bank->lock, flags);
+	raw_spin_unlock_irqrestore(&bank->lock, flags);
 
 	if (type & (IRQ_TYPE_LEVEL_LOW | IRQ_TYPE_LEVEL_HIGH))
 		__irq_set_handler_locked(d->irq, handle_level_irq);
@@ -641,14 +641,14 @@ static int omap_set_gpio_wakeup(struct gpio_bank *bank, int gpio, int enable)
 		return -EINVAL;
 	}
 
-	spin_lock_irqsave(&bank->lock, flags);
+	raw_spin_lock_irqsave(&bank->lock, flags);
 	if (enable)
 		bank->context.wake_en |= gpio_bit;
 	else
 		bank->context.wake_en &= ~gpio_bit;
 
 	writel_relaxed(bank->context.wake_en, bank->base + bank->regs->wkup_en);
-	spin_unlock_irqrestore(&bank->lock, flags);
+	raw_spin_unlock_irqrestore(&bank->lock, flags);
 
 	return 0;
 }
@@ -683,7 +683,7 @@ static int omap_gpio_request(struct gpio_chip *chip, unsigned offset)
 	if (!BANK_USED(bank))
 		pm_runtime_get_sync(bank->dev);
 
-	spin_lock_irqsave(&bank->lock, flags);
+	raw_spin_lock_irqsave(&bank->lock, flags);
 	/* Set trigger to none. You need to enable the desired trigger with
 	 * request_irq() or set_irq_type(). Only do this if the IRQ line has
 	 * not already been requested.
@@ -693,7 +693,7 @@ static int omap_gpio_request(struct gpio_chip *chip, unsigned offset)
 		omap_enable_gpio_module(bank, offset);
 	}
 	bank->mod_usage |= BIT(offset);
-	spin_unlock_irqrestore(&bank->lock, flags);
+	raw_spin_unlock_irqrestore(&bank->lock, flags);
 
 	return 0;
 }
@@ -703,11 +703,11 @@ static void omap_gpio_free(struct gpio_chip *chip, unsigned offset)
 	struct gpio_bank *bank = container_of(chip, struct gpio_bank, chip);
 	unsigned long flags;
 
-	spin_lock_irqsave(&bank->lock, flags);
+	raw_spin_lock_irqsave(&bank->lock, flags);
 	bank->mod_usage &= ~(BIT(offset));
 	omap_disable_gpio_module(bank, offset);
 	omap_reset_gpio(bank, bank->chip.base + offset);
-	spin_unlock_irqrestore(&bank->lock, flags);
+	raw_spin_unlock_irqrestore(&bank->lock, flags);
 
 	/*
 	 * If this is the last gpio to be freed in the bank,
@@ -810,9 +810,9 @@ static unsigned int omap_gpio_irq_startup(struct irq_data *d)
 	if (!BANK_USED(bank))
 		pm_runtime_get_sync(bank->dev);
 
-	spin_lock_irqsave(&bank->lock, flags);
+	raw_spin_lock_irqsave(&bank->lock, flags);
 	omap_gpio_init_irq(bank, gpio, offset);
-	spin_unlock_irqrestore(&bank->lock, flags);
+	raw_spin_unlock_irqrestore(&bank->lock, flags);
 	omap_gpio_unmask_irq(d);
 
 	return 0;
@@ -825,12 +825,12 @@ static void omap_gpio_irq_shutdown(struct irq_data *d)
 	unsigned long flags;
 	unsigned offset = GPIO_INDEX(bank, gpio);
 
-	spin_lock_irqsave(&bank->lock, flags);
+	raw_spin_lock_irqsave(&bank->lock, flags);
 	gpiochip_unlock_as_irq(&bank->chip, offset);
 	bank->irq_usage &= ~(BIT(offset));
 	omap_disable_gpio_module(bank, offset);
 	omap_reset_gpio(bank, gpio);
-	spin_unlock_irqrestore(&bank->lock, flags);
+	raw_spin_unlock_irqrestore(&bank->lock, flags);
 
 	/*
 	 * If this is the last IRQ to be freed in the bank,
@@ -854,10 +854,10 @@ static void omap_gpio_mask_irq(struct irq_data *d)
 	unsigned int gpio = omap_irq_to_gpio(bank, d->hwirq);
 	unsigned long flags;
 
-	spin_lock_irqsave(&bank->lock, flags);
+	raw_spin_lock_irqsave(&bank->lock, flags);
 	omap_set_gpio_irqenable(bank, gpio, 0);
 	omap_set_gpio_triggering(bank, GPIO_INDEX(bank, gpio), IRQ_TYPE_NONE);
-	spin_unlock_irqrestore(&bank->lock, flags);
+	raw_spin_unlock_irqrestore(&bank->lock, flags);
 }
 
 static void omap_gpio_unmask_irq(struct irq_data *d)
@@ -868,7 +868,7 @@ static void omap_gpio_unmask_irq(struct irq_data *d)
 	u32 trigger = irqd_get_trigger_type(d);
 	unsigned long flags;
 
-	spin_lock_irqsave(&bank->lock, flags);
+	raw_spin_lock_irqsave(&bank->lock, flags);
 	if (trigger)
 		omap_set_gpio_triggering(bank, GPIO_INDEX(bank, gpio), trigger);
 
@@ -880,7 +880,7 @@ static void omap_gpio_unmask_irq(struct irq_data *d)
 	}
 
 	omap_set_gpio_irqenable(bank, gpio, 1);
-	spin_unlock_irqrestore(&bank->lock, flags);
+	raw_spin_unlock_irqrestore(&bank->lock, flags);
 }
 
 /*---------------------------------------------------------------------*/
@@ -893,9 +893,9 @@ static int omap_mpuio_suspend_noirq(struct device *dev)
 					OMAP_MPUIO_GPIO_MASKIT / bank->stride;
 	unsigned long		flags;
 
-	spin_lock_irqsave(&bank->lock, flags);
+	raw_spin_lock_irqsave(&bank->lock, flags);
 	writel_relaxed(0xffff & ~bank->context.wake_en, mask_reg);
-	spin_unlock_irqrestore(&bank->lock, flags);
+	raw_spin_unlock_irqrestore(&bank->lock, flags);
 
 	return 0;
 }
@@ -908,9 +908,9 @@ static int omap_mpuio_resume_noirq(struct device *dev)
 					OMAP_MPUIO_GPIO_MASKIT / bank->stride;
 	unsigned long		flags;
 
-	spin_lock_irqsave(&bank->lock, flags);
+	raw_spin_lock_irqsave(&bank->lock, flags);
 	writel_relaxed(bank->context.wake_en, mask_reg);
-	spin_unlock_irqrestore(&bank->lock, flags);
+	raw_spin_unlock_irqrestore(&bank->lock, flags);
 
 	return 0;
 }
@@ -956,9 +956,9 @@ static int omap_gpio_get_direction(struct gpio_chip *chip, unsigned offset)
 
 	bank = container_of(chip, struct gpio_bank, chip);
 	reg = bank->base + bank->regs->direction;
-	spin_lock_irqsave(&bank->lock, flags);
+	raw_spin_lock_irqsave(&bank->lock, flags);
 	dir = !!(readl_relaxed(reg) & BIT(offset));
-	spin_unlock_irqrestore(&bank->lock, flags);
+	raw_spin_unlock_irqrestore(&bank->lock, flags);
 	return dir;
 }
 
@@ -968,9 +968,9 @@ static int omap_gpio_input(struct gpio_chip *chip, unsigned offset)
 	unsigned long flags;
 
 	bank = container_of(chip, struct gpio_bank, chip);
-	spin_lock_irqsave(&bank->lock, flags);
+	raw_spin_lock_irqsave(&bank->lock, flags);
 	omap_set_gpio_direction(bank, offset, 1);
-	spin_unlock_irqrestore(&bank->lock, flags);
+	raw_spin_unlock_irqrestore(&bank->lock, flags);
 	return 0;
 }
 
@@ -994,10 +994,10 @@ static int omap_gpio_output(struct gpio_chip *chip, unsigned offset, int value)
 	unsigned long flags;
 
 	bank = container_of(chip, struct gpio_bank, chip);
-	spin_lock_irqsave(&bank->lock, flags);
+	raw_spin_lock_irqsave(&bank->lock, flags);
 	bank->set_dataout(bank, offset, value);
 	omap_set_gpio_direction(bank, offset, 0);
-	spin_unlock_irqrestore(&bank->lock, flags);
+	raw_spin_unlock_irqrestore(&bank->lock, flags);
 	return 0;
 }
 
@@ -1009,9 +1009,9 @@ static int omap_gpio_debounce(struct gpio_chip *chip, unsigned offset,
 
 	bank = container_of(chip, struct gpio_bank, chip);
 
-	spin_lock_irqsave(&bank->lock, flags);
+	raw_spin_lock_irqsave(&bank->lock, flags);
 	omap2_set_gpio_debounce(bank, offset, debounce);
-	spin_unlock_irqrestore(&bank->lock, flags);
+	raw_spin_unlock_irqrestore(&bank->lock, flags);
 
 	return 0;
 }
@@ -1022,9 +1022,9 @@ static void omap_gpio_set(struct gpio_chip *chip, unsigned offset, int value)
 	unsigned long flags;
 
 	bank = container_of(chip, struct gpio_bank, chip);
-	spin_lock_irqsave(&bank->lock, flags);
+	raw_spin_lock_irqsave(&bank->lock, flags);
 	bank->set_dataout(bank, offset, value);
-	spin_unlock_irqrestore(&bank->lock, flags);
+	raw_spin_unlock_irqrestore(&bank->lock, flags);
 }
 
 /*---------------------------------------------------------------------*/
@@ -1250,7 +1250,7 @@ static int omap_gpio_probe(struct platform_device *pdev)
 	else
 		bank->set_dataout = omap_set_gpio_dataout_mask;
 
-	spin_lock_init(&bank->lock);
+	raw_spin_lock_init(&bank->lock);
 
 	/* Static mapping, never released */
 	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
@@ -1297,7 +1297,7 @@ static int omap_gpio_runtime_suspend(struct device *dev)
 	unsigned long flags;
 	u32 wake_low, wake_hi;
 
-	spin_lock_irqsave(&bank->lock, flags);
+	raw_spin_lock_irqsave(&bank->lock, flags);
 
 	/*
 	 * Only edges can generate a wakeup event to the PRCM.
@@ -1350,7 +1350,7 @@ static int omap_gpio_runtime_suspend(struct device *dev)
 				bank->get_context_loss_count(bank->dev);
 
 	omap_gpio_dbck_disable(bank);
-	spin_unlock_irqrestore(&bank->lock, flags);
+	raw_spin_unlock_irqrestore(&bank->lock, flags);
 
 	return 0;
 }
@@ -1365,7 +1365,7 @@ static int omap_gpio_runtime_resume(struct device *dev)
 	unsigned long flags;
 	int c;
 
-	spin_lock_irqsave(&bank->lock, flags);
+	raw_spin_lock_irqsave(&bank->lock, flags);
 
 	/*
 	 * On the first resume during the probe, the context has not
@@ -1401,14 +1401,14 @@ static int omap_gpio_runtime_resume(struct device *dev)
 			if (c != bank->context_loss_count) {
 				omap_gpio_restore_context(bank);
 			} else {
-				spin_unlock_irqrestore(&bank->lock, flags);
+				raw_spin_unlock_irqrestore(&bank->lock, flags);
 				return 0;
 			}
 		}
 	}
 
 	if (!bank->workaround_enabled) {
-		spin_unlock_irqrestore(&bank->lock, flags);
+		raw_spin_unlock_irqrestore(&bank->lock, flags);
 		return 0;
 	}
 
@@ -1463,7 +1463,7 @@ static int omap_gpio_runtime_resume(struct device *dev)
 	}
 
 	bank->workaround_enabled = false;
-	spin_unlock_irqrestore(&bank->lock, flags);
+	raw_spin_unlock_irqrestore(&bank->lock, flags);
 
 	return 0;
 }
-- 
2.1.4

Re: [PATCH] gpio: omap: use raw locks for locking

[Javier Martinez Canillas]

Hello Sebastian,

Thanks a lot for your patch.

On Thu, Feb 12, 2015 at 5:10 PM, Sebastian Andrzej Siewior
<bigeasy@linutronix.de> wrote:
> This patch converts gpio_bank.lock from a spin_lock into a
> raw_spin_lock. The call path to access this lock is always under a
> raw_spin_lock, for instance
> - __setup_irq() holds &desc->lock with irq off
>   + __irq_set_trigger()
>    + omap_gpio_irq_type()
>
> - handle_level_irq() (runs with irqs off therefore raw locks)
>   + mask_ack_irq()
>    + omap_gpio_mask_irq()
>

Agreed that raw_spin_lock should be used instead of spin_lock since
afaiu those are converted to a rt-mutex in PREEMPT_RT and so they
might sleep.

> This fixes the obvious backtrace on -RT. However I noticed two cases
> where it looks wrong and this is not limited to -RT:
> - omap_gpio_irq_type() is called with IRQ off and has an conditional
>   call to pm_runtime_get_sync() which may sleep. Either it may happen or
>   it may not happen but pm_runtime_get_sync() should not be called in an
>   atomic section.
>
> - omap_gpio_debounce() is holding the lock with IRQs off.
>   + omap2_set_gpio_debounce()
>    + clk_prepare_enable()
>     + clk_prepare() this one might sleep.
>   The number of users of gpiod_set_debounce() / gpio_set_debounce()
>   looks low but still this is not good.
>

Right, those are bugs regardless of PREEMPT_RT or not as you said.
I'll add it to my TODO list, thanks for finding those.

> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> ---
>  drivers/gpio/gpio-omap.c | 78 ++++++++++++++++++++++++------------------------
>  1 file changed, 39 insertions(+), 39 deletions(-)
>

Acked-by: Javier Martinez Canillas <javier@dowhile0.org>

Best regards,
Javier

Re: [PATCH] gpio: omap: use raw locks for locking

[Sebastian Andrzej Siewior]

On 02/16/2015 09:54 AM, Javier Martinez Canillas wrote:
> Hello Sebastian,

Hello Javier,

> Right, those are bugs regardless of PREEMPT_RT or not as you said.
> I'll add it to my TODO list, thanks for finding those.

Thanks.

> Acked-by: Javier Martinez Canillas <javier@dowhile0.org>
> 
> Best regards,
> Javier

Sebastian

Re: [PATCH] gpio: omap: use raw locks for locking

[Javier Martinez Canillas]

Hello Sebastian,

On Thu, Feb 12, 2015 at 5:10 PM, Sebastian Andrzej Siewior
<bigeasy@linutronix.de> wrote:
> This patch converts gpio_bank.lock from a spin_lock into a
> raw_spin_lock. The call path to access this lock is always under a
> raw_spin_lock, for instance
> - __setup_irq() holds &desc->lock with irq off
>   + __irq_set_trigger()
>    + omap_gpio_irq_type()
>
> - handle_level_irq() (runs with irqs off therefore raw locks)
>   + mask_ack_irq()
>    + omap_gpio_mask_irq()
>
> This fixes the obvious backtrace on -RT. However I noticed two cases
> where it looks wrong and this is not limited to -RT:
> - omap_gpio_irq_type() is called with IRQ off and has an conditional
>   call to pm_runtime_get_sync() which may sleep. Either it may happen or
>   it may not happen but pm_runtime_get_sync() should not be called in an
>   atomic section.
>
> - omap_gpio_debounce() is holding the lock with IRQs off.
>   + omap2_set_gpio_debounce()
>    + clk_prepare_enable()
>     + clk_prepare() this one might sleep.
>   The number of users of gpiod_set_debounce() / gpio_set_debounce()
>   looks low but still this is not good.
>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> ---

I had already acked the first time you posted this [0] but you didn't
carry the tag so here goes again:

Acked-by: Javier Martinez Canillas <javier@dowhile0.org>

Best regards,
Javier

[0]: https://patchwork.ozlabs.org/patch/439249/
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Re: [PATCH] gpio: omap: use raw locks for locking

[Linus Walleij]

On Thu, Feb 12, 2015 at 5:10 PM, Sebastian Andrzej Siewior
<bigeasy@linutronix.de> wrote:

> This patch converts gpio_bank.lock from a spin_lock into a
> raw_spin_lock. The call path to access this lock is always under a
> raw_spin_lock, for instance
> - __setup_irq() holds &desc->lock with irq off
>   + __irq_set_trigger()
>    + omap_gpio_irq_type()
>
> - handle_level_irq() (runs with irqs off therefore raw locks)
>   + mask_ack_irq()
>    + omap_gpio_mask_irq()
>
> This fixes the obvious backtrace on -RT. However I noticed two cases
> where it looks wrong and this is not limited to -RT:
> - omap_gpio_irq_type() is called with IRQ off and has an conditional
>   call to pm_runtime_get_sync() which may sleep. Either it may happen or
>   it may not happen but pm_runtime_get_sync() should not be called in an
>   atomic section.
>
> - omap_gpio_debounce() is holding the lock with IRQs off.
>   + omap2_set_gpio_debounce()
>    + clk_prepare_enable()
>     + clk_prepare() this one might sleep.
>   The number of users of gpiod_set_debounce() / gpio_set_debounce()
>   looks low but still this is not good.
>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

This doesn't apply to the current development tree.

Can you rebase this patch in Torvalds' HEAD, add Javier's ACK
and resend?

Please put me on the To: line, I have no time to read all mail that
I'm only CC on.

Yours,
Linus Walleij

Re: [PATCH] gpio: omap: use raw locks for locking

[Sebastian Andrzej Siewior]

On 06/30/2015 08:45 AM, Linus Walleij wrote:
> This doesn't apply to the current development tree.

it has been pointed out to me.

> Can you rebase this patch in Torvalds' HEAD, add Javier's ACK
> and resend?

I will do it once I'm done roasted :)

> Please put me on the To: line, I have no time to read all mail that
> I'm only CC on.
noted. This might been the problem while it hasn't been applied the
first time I posted it.

> Yours,
> Linus Walleij

Sebastian

Re: [PATCH] gpio: omap: use raw locks for locking

[Thomas Gleixner]

On Mon, 27 Jul 2015, Sebastian Andrzej Siewior wrote:
> On 07/27/2015 02:50 PM, Linus Walleij wrote:
> > Patch applied.
> thanks.
> 
> > 
> > Now this question appear in my head:
> > 
> > Is drivers/gpio full of stuff that will not work with the -RT kernel,
> > and is this a change that should be done mutatis mutandis on
> > all the GPIO drivers?
> 
> I described two call paths where you need a rawlock_t. If your gpio
> driver uses irq_chip_generic then you a rawlock here and things should
> be fine.
> 
> In general: If your gpio controller acts as an interrupts controller
> (that is via chained handler) then you need the raw-locks if you need
> any locking (if you have a write 1 to mask/unmask/enable/disable
> register then you probably don't need any locking here at all). If the
> gpio controller does not act as an interrupt controller than the
> spinlock_t type should be enough.
> If your gpio-interrupt controller requests its interrupt via
> requested_threaded_irq() then it should do handle_nested_irq() and a
> mutex is probably used for locking.
> 
> Using request_irq() with "0" flags is kind of broken. It works in
> IRQ-context and delivers the interrupts with generic_handle_irq() and
> this one passes it the handler (like handle_edge_irq() /
> handle_level_irq()) which takes a raw_lock. Now, if you boot the
> vanilla kernel with threadedirq then the irq-handler runs in threaded
> context and you can't take a spinlock here anymore. So I think you
> should use here IRQF_NO_THREAD here (and the raw lock type). I added
> tglx on Cc: to back up because it is Monday.

Indeed it was monday.

It's an RT only problem. On mainline spinlock resovles to raw_spinlock.

Now there is the story what breaks in RT:

1) irq controller specific locks which are taken in the irq chip
   callbacks need to be raw_spinlocks because these functions are
   called with irq_desc->lock helds and interrupts disabled.

   If that irq chip lock is not raw you rightfully get a backtrace.

   raw_spinlock_irq(&desc->lock);
   chip->callback()
     spin_lock(chip_private_lock);
       might_sleep() triggers

2) locks which are taken in chained interrupt handlers need to be raw
   on RT. These handlers run in hard interrupt context so again
   might_sleep() rightfully complains.

Thanks,

	tglx

Re: [PATCH] gpio: omap: use raw locks for locking

[Sebastian Andrzej Siewior]

On 07/27/2015 02:50 PM, Linus Walleij wrote:
> Patch applied.
thanks.

> 
> Now this question appear in my head:
> 
> Is drivers/gpio full of stuff that will not work with the -RT kernel,
> and is this a change that should be done mutatis mutandis on
> all the GPIO drivers?

I described two call paths where you need a rawlock_t. If your gpio
driver uses irq_chip_generic then you a rawlock here and things should
be fine.

In general: If your gpio controller acts as an interrupts controller
(that is via chained handler) then you need the raw-locks if you need
any locking (if you have a write 1 to mask/unmask/enable/disable
register then you probably don't need any locking here at all). If the
gpio controller does not act as an interrupt controller than the
spinlock_t type should be enough.
If your gpio-interrupt controller requests its interrupt via
requested_threaded_irq() then it should do handle_nested_irq() and a
mutex is probably used for locking.

Using request_irq() with "0" flags is kind of broken. It works in
IRQ-context and delivers the interrupts with generic_handle_irq() and
this one passes it the handler (like handle_edge_irq() /
handle_level_irq()) which takes a raw_lock. Now, if you boot the
vanilla kernel with threadedirq then the irq-handler runs in threaded
context and you can't take a spinlock here anymore. So I think you
should use here IRQF_NO_THREAD here (and the raw lock type). I added
tglx on Cc: to back up because it is Monday.

> Yours,
> Linus Walleij
> 

Sebastian

Re: [PATCH] gpio: omap: use raw locks for locking

[Linus Walleij]

On Tue, Jul 21, 2015 at 6:26 PM, Sebastian Andrzej Siewior
<bigeasy@linutronix.de> wrote:

> This patch converts gpio_bank.lock from a spin_lock into a
> raw_spin_lock. The call path is to access this lock is always under a
> raw_spin_lock, for instance
> - __setup_irq() holds &desc->lock with irq off
>   + __irq_set_trigger()
>    + omap_gpio_irq_type()
>
> - handle_level_irq() (runs with irqs off therefore raw locks)
>   + mask_ack_irq()
>    + omap_gpio_mask_irq()
>
> This fixes the obvious backtrace on -RT. However the locking vs context
> is not and this is not limited to -RT:
> - omap_gpio_irq_type() is called with IRQ off and has an conditional
>   call to pm_runtime_get_sync() which may sleep. Either it may happen or
>   it may not happen but pm_runtime_get_sync() should not be called with
>   irqs off.
>
> - omap_gpio_debounce() is holding the lock with IRQs off.
>   + omap2_set_gpio_debounce()
>    + clk_prepare_enable()
>     + clk_prepare() this one might sleep.
>   The number of users of gpiod_set_debounce() / gpio_set_debounce()
>   looks low but still this is not good.
>
> Acked-by: Javier Martinez Canillas <javier@dowhile0.org>
> Acked-by: Santosh Shilimkar <ssantosh@kernel.org>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

Patch applied.

Now this question appear in my head:

Is drivers/gpio full of stuff that will not work with the -RT kernel,
and is this a change that should be done mutatis mutandis on
all the GPIO drivers?

Yours,
Linus Walleij

[PATCH] gpio: omap: use raw locks for locking

[Sebastian Andrzej Siewior]

This patch converts gpio_bank.lock from a spin_lock into a
raw_spin_lock. The call path is to access this lock is always under a
raw_spin_lock, for instance
- __setup_irq() holds &desc->lock with irq off
  + __irq_set_trigger()
   + omap_gpio_irq_type()

- handle_level_irq() (runs with irqs off therefore raw locks)
  + mask_ack_irq()
   + omap_gpio_mask_irq()

This fixes the obvious backtrace on -RT. However the locking vs context
is not and this is not limited to -RT:
- omap_gpio_irq_type() is called with IRQ off and has an conditional
  call to pm_runtime_get_sync() which may sleep. Either it may happen or
  it may not happen but pm_runtime_get_sync() should not be called with
  irqs off.

- omap_gpio_debounce() is holding the lock with IRQs off.
  + omap2_set_gpio_debounce()
   + clk_prepare_enable()
    + clk_prepare() this one might sleep.
  The number of users of gpiod_set_debounce() / gpio_set_debounce()
  looks low but still this is not good.

Acked-by: Javier Martinez Canillas <javier@dowhile0.org>
Acked-by: Santosh Shilimkar <ssantosh@kernel.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 drivers/gpio/gpio-omap.c | 82 ++++++++++++++++++++++++------------------------
 1 file changed, 41 insertions(+), 41 deletions(-)

diff --git a/drivers/gpio/gpio-omap.c b/drivers/gpio/gpio-omap.c
index 61a731ff9a07..f56de8de9c55 100644
--- a/drivers/gpio/gpio-omap.c
+++ b/drivers/gpio/gpio-omap.c
@@ -57,7 +57,7 @@ struct gpio_bank {
 	u32 saved_datain;
 	u32 level_mask;
 	u32 toggle_mask;
-	spinlock_t lock;
+	raw_spinlock_t lock;
 	struct gpio_chip chip;
 	struct clk *dbck;
 	u32 mod_usage;
@@ -498,19 +498,19 @@ static int omap_gpio_irq_type(struct irq_data *d, unsigned type)
 	if (!BANK_USED(bank))
 		pm_runtime_get_sync(bank->dev);
 
-	spin_lock_irqsave(&bank->lock, flags);
+	raw_spin_lock_irqsave(&bank->lock, flags);
 	retval = omap_set_gpio_triggering(bank, offset, type);
 	if (retval) {
-		spin_unlock_irqrestore(&bank->lock, flags);
+		raw_spin_unlock_irqrestore(&bank->lock, flags);
 		goto error;
 	}
 	omap_gpio_init_irq(bank, offset);
 	if (!omap_gpio_is_input(bank, offset)) {
-		spin_unlock_irqrestore(&bank->lock, flags);
+		raw_spin_unlock_irqrestore(&bank->lock, flags);
 		retval = -EINVAL;
 		goto error;
 	}
-	spin_unlock_irqrestore(&bank->lock, flags);
+	raw_spin_unlock_irqrestore(&bank->lock, flags);
 
 	if (type & (IRQ_TYPE_LEVEL_LOW | IRQ_TYPE_LEVEL_HIGH))
 		__irq_set_handler_locked(d->irq, handle_level_irq);
@@ -636,14 +636,14 @@ static int omap_set_gpio_wakeup(struct gpio_bank *bank, unsigned offset,
 		return -EINVAL;
 	}
 
-	spin_lock_irqsave(&bank->lock, flags);
+	raw_spin_lock_irqsave(&bank->lock, flags);
 	if (enable)
 		bank->context.wake_en |= gpio_bit;
 	else
 		bank->context.wake_en &= ~gpio_bit;
 
 	writel_relaxed(bank->context.wake_en, bank->base + bank->regs->wkup_en);
-	spin_unlock_irqrestore(&bank->lock, flags);
+	raw_spin_unlock_irqrestore(&bank->lock, flags);
 
 	return 0;
 }
@@ -669,10 +669,10 @@ static int omap_gpio_request(struct gpio_chip *chip, unsigned offset)
 	if (!BANK_USED(bank))
 		pm_runtime_get_sync(bank->dev);
 
-	spin_lock_irqsave(&bank->lock, flags);
+	raw_spin_lock_irqsave(&bank->lock, flags);
 	omap_enable_gpio_module(bank, offset);
 	bank->mod_usage |= BIT(offset);
-	spin_unlock_irqrestore(&bank->lock, flags);
+	raw_spin_unlock_irqrestore(&bank->lock, flags);
 
 	return 0;
 }
@@ -682,14 +682,14 @@ static void omap_gpio_free(struct gpio_chip *chip, unsigned offset)
 	struct gpio_bank *bank = container_of(chip, struct gpio_bank, chip);
 	unsigned long flags;
 
-	spin_lock_irqsave(&bank->lock, flags);
+	raw_spin_lock_irqsave(&bank->lock, flags);
 	bank->mod_usage &= ~(BIT(offset));
 	if (!LINE_USED(bank->irq_usage, offset)) {
 		omap_set_gpio_direction(bank, offset, 1);
 		omap_clear_gpio_debounce(bank, offset);
 	}
 	omap_disable_gpio_module(bank, offset);
-	spin_unlock_irqrestore(&bank->lock, flags);
+	raw_spin_unlock_irqrestore(&bank->lock, flags);
 
 	/*
 	 * If this is the last gpio to be freed in the bank,
@@ -791,7 +791,7 @@ static unsigned int omap_gpio_irq_startup(struct irq_data *d)
 	if (!BANK_USED(bank))
 		pm_runtime_get_sync(bank->dev);
 
-	spin_lock_irqsave(&bank->lock, flags);
+	raw_spin_lock_irqsave(&bank->lock, flags);
 
 	if (!LINE_USED(bank->mod_usage, offset))
 		omap_set_gpio_direction(bank, offset, 1);
@@ -800,12 +800,12 @@ static unsigned int omap_gpio_irq_startup(struct irq_data *d)
 	omap_enable_gpio_module(bank, offset);
 	bank->irq_usage |= BIT(offset);
 
-	spin_unlock_irqrestore(&bank->lock, flags);
+	raw_spin_unlock_irqrestore(&bank->lock, flags);
 	omap_gpio_unmask_irq(d);
 
 	return 0;
 err:
-	spin_unlock_irqrestore(&bank->lock, flags);
+	raw_spin_unlock_irqrestore(&bank->lock, flags);
 	if (!BANK_USED(bank))
 		pm_runtime_put(bank->dev);
 	return -EINVAL;
@@ -817,7 +817,7 @@ static void omap_gpio_irq_shutdown(struct irq_data *d)
 	unsigned long flags;
 	unsigned offset = d->hwirq;
 
-	spin_lock_irqsave(&bank->lock, flags);
+	raw_spin_lock_irqsave(&bank->lock, flags);
 	bank->irq_usage &= ~(BIT(offset));
 	omap_set_gpio_irqenable(bank, offset, 0);
 	omap_clear_gpio_irqstatus(bank, offset);
@@ -825,7 +825,7 @@ static void omap_gpio_irq_shutdown(struct irq_data *d)
 	if (!LINE_USED(bank->mod_usage, offset))
 		omap_clear_gpio_debounce(bank, offset);
 	omap_disable_gpio_module(bank, offset);
-	spin_unlock_irqrestore(&bank->lock, flags);
+	raw_spin_unlock_irqrestore(&bank->lock, flags);
 
 	/*
 	 * If this is the last IRQ to be freed in the bank,
@@ -849,10 +849,10 @@ static void omap_gpio_mask_irq(struct irq_data *d)
 	unsigned offset = d->hwirq;
 	unsigned long flags;
 
-	spin_lock_irqsave(&bank->lock, flags);
+	raw_spin_lock_irqsave(&bank->lock, flags);
 	omap_set_gpio_irqenable(bank, offset, 0);
 	omap_set_gpio_triggering(bank, offset, IRQ_TYPE_NONE);
-	spin_unlock_irqrestore(&bank->lock, flags);
+	raw_spin_unlock_irqrestore(&bank->lock, flags);
 }
 
 static void omap_gpio_unmask_irq(struct irq_data *d)
@@ -862,7 +862,7 @@ static void omap_gpio_unmask_irq(struct irq_data *d)
 	u32 trigger = irqd_get_trigger_type(d);
 	unsigned long flags;
 
-	spin_lock_irqsave(&bank->lock, flags);
+	raw_spin_lock_irqsave(&bank->lock, flags);
 	if (trigger)
 		omap_set_gpio_triggering(bank, offset, trigger);
 
@@ -874,7 +874,7 @@ static void omap_gpio_unmask_irq(struct irq_data *d)
 	}
 
 	omap_set_gpio_irqenable(bank, offset, 1);
-	spin_unlock_irqrestore(&bank->lock, flags);
+	raw_spin_unlock_irqrestore(&bank->lock, flags);
 }
 
 /*---------------------------------------------------------------------*/
@@ -887,9 +887,9 @@ static int omap_mpuio_suspend_noirq(struct device *dev)
 					OMAP_MPUIO_GPIO_MASKIT / bank->stride;
 	unsigned long		flags;
 
-	spin_lock_irqsave(&bank->lock, flags);
+	raw_spin_lock_irqsave(&bank->lock, flags);
 	writel_relaxed(0xffff & ~bank->context.wake_en, mask_reg);
-	spin_unlock_irqrestore(&bank->lock, flags);
+	raw_spin_unlock_irqrestore(&bank->lock, flags);
 
 	return 0;
 }
@@ -902,9 +902,9 @@ static int omap_mpuio_resume_noirq(struct device *dev)
 					OMAP_MPUIO_GPIO_MASKIT / bank->stride;
 	unsigned long		flags;
 
-	spin_lock_irqsave(&bank->lock, flags);
+	raw_spin_lock_irqsave(&bank->lock, flags);
 	writel_relaxed(bank->context.wake_en, mask_reg);
-	spin_unlock_irqrestore(&bank->lock, flags);
+	raw_spin_unlock_irqrestore(&bank->lock, flags);
 
 	return 0;
 }
@@ -950,9 +950,9 @@ static int omap_gpio_get_direction(struct gpio_chip *chip, unsigned offset)
 
 	bank = container_of(chip, struct gpio_bank, chip);
 	reg = bank->base + bank->regs->direction;
-	spin_lock_irqsave(&bank->lock, flags);
+	raw_spin_lock_irqsave(&bank->lock, flags);
 	dir = !!(readl_relaxed(reg) & BIT(offset));
-	spin_unlock_irqrestore(&bank->lock, flags);
+	raw_spin_unlock_irqrestore(&bank->lock, flags);
 	return dir;
 }
 
@@ -962,9 +962,9 @@ static int omap_gpio_input(struct gpio_chip *chip, unsigned offset)
 	unsigned long flags;
 
 	bank = container_of(chip, struct gpio_bank, chip);
-	spin_lock_irqsave(&bank->lock, flags);
+	raw_spin_lock_irqsave(&bank->lock, flags);
 	omap_set_gpio_direction(bank, offset, 1);
-	spin_unlock_irqrestore(&bank->lock, flags);
+	raw_spin_unlock_irqrestore(&bank->lock, flags);
 	return 0;
 }
 
@@ -986,10 +986,10 @@ static int omap_gpio_output(struct gpio_chip *chip, unsigned offset, int value)
 	unsigned long flags;
 
 	bank = container_of(chip, struct gpio_bank, chip);
-	spin_lock_irqsave(&bank->lock, flags);
+	raw_spin_lock_irqsave(&bank->lock, flags);
 	bank->set_dataout(bank, offset, value);
 	omap_set_gpio_direction(bank, offset, 0);
-	spin_unlock_irqrestore(&bank->lock, flags);
+	raw_spin_unlock_irqrestore(&bank->lock, flags);
 	return 0;
 }
 
@@ -1001,9 +1001,9 @@ static int omap_gpio_debounce(struct gpio_chip *chip, unsigned offset,
 
 	bank = container_of(chip, struct gpio_bank, chip);
 
-	spin_lock_irqsave(&bank->lock, flags);
+	raw_spin_lock_irqsave(&bank->lock, flags);
 	omap2_set_gpio_debounce(bank, offset, debounce);
-	spin_unlock_irqrestore(&bank->lock, flags);
+	raw_spin_unlock_irqrestore(&bank->lock, flags);
 
 	return 0;
 }
@@ -1014,9 +1014,9 @@ static void omap_gpio_set(struct gpio_chip *chip, unsigned offset, int value)
 	unsigned long flags;
 
 	bank = container_of(chip, struct gpio_bank, chip);
-	spin_lock_irqsave(&bank->lock, flags);
+	raw_spin_lock_irqsave(&bank->lock, flags);
 	bank->set_dataout(bank, offset, value);
-	spin_unlock_irqrestore(&bank->lock, flags);
+	raw_spin_unlock_irqrestore(&bank->lock, flags);
 }
 
 /*---------------------------------------------------------------------*/
@@ -1213,7 +1213,7 @@ static int omap_gpio_probe(struct platform_device *pdev)
 	else
 		bank->set_dataout = omap_set_gpio_dataout_mask;
 
-	spin_lock_init(&bank->lock);
+	raw_spin_lock_init(&bank->lock);
 
 	/* Static mapping, never released */
 	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
@@ -1271,7 +1271,7 @@ static int omap_gpio_runtime_suspend(struct device *dev)
 	unsigned long flags;
 	u32 wake_low, wake_hi;
 
-	spin_lock_irqsave(&bank->lock, flags);
+	raw_spin_lock_irqsave(&bank->lock, flags);
 
 	/*
 	 * Only edges can generate a wakeup event to the PRCM.
@@ -1324,7 +1324,7 @@ static int omap_gpio_runtime_suspend(struct device *dev)
 				bank->get_context_loss_count(bank->dev);
 
 	omap_gpio_dbck_disable(bank);
-	spin_unlock_irqrestore(&bank->lock, flags);
+	raw_spin_unlock_irqrestore(&bank->lock, flags);
 
 	return 0;
 }
@@ -1339,7 +1339,7 @@ static int omap_gpio_runtime_resume(struct device *dev)
 	unsigned long flags;
 	int c;
 
-	spin_lock_irqsave(&bank->lock, flags);
+	raw_spin_lock_irqsave(&bank->lock, flags);
 
 	/*
 	 * On the first resume during the probe, the context has not
@@ -1375,14 +1375,14 @@ static int omap_gpio_runtime_resume(struct device *dev)
 			if (c != bank->context_loss_count) {
 				omap_gpio_restore_context(bank);
 			} else {
-				spin_unlock_irqrestore(&bank->lock, flags);
+				raw_spin_unlock_irqrestore(&bank->lock, flags);
 				return 0;
 			}
 		}
 	}
 
 	if (!bank->workaround_enabled) {
-		spin_unlock_irqrestore(&bank->lock, flags);
+		raw_spin_unlock_irqrestore(&bank->lock, flags);
 		return 0;
 	}
 
@@ -1437,7 +1437,7 @@ static int omap_gpio_runtime_resume(struct device *dev)
 	}
 
 	bank->workaround_enabled = false;
-	spin_unlock_irqrestore(&bank->lock, flags);
+	raw_spin_unlock_irqrestore(&bank->lock, flags);
 
 	return 0;
 }
-- 
2.1.4