[PATCH for next v1 0/2] gpio: few clean up patches to replace spin_lock_irqsave with spin_lock
There is no need to use API with _irqsave in hard IRQ handler, So replace those with spin_lock.
Luo Jiaxing (2): gpio: omap: Replace raw_spin_lock_irqsave with raw_spin_lock in omap_gpio_irq_handler() gpio: grgpio: Replace spin_lock_irqsave with spin_lock in grgpio_irq_handler()
drivers/gpio/gpio-grgpio.c | 5 ++--- drivers/gpio/gpio-omap.c | 15 ++++++--------- 2 files changed, 8 insertions(+), 12 deletions(-)
There is no need to use API with _irqsave in omap_gpio_irq_handler(), because it already be in a irq-disabled context.
Signed-off-by: Luo Jiaxing luojiaxing@huawei.com --- drivers/gpio/gpio-omap.c | 15 ++++++--------- 1 file changed, 6 insertions(+), 9 deletions(-)
diff --git a/drivers/gpio/gpio-omap.c b/drivers/gpio/gpio-omap.c index 41952bb..dc8bbf4 100644 --- a/drivers/gpio/gpio-omap.c +++ b/drivers/gpio/gpio-omap.c @@ -560,8 +560,6 @@ static irqreturn_t omap_gpio_irq_handler(int irq, void *gpiobank) u32 enabled, isr, edge; unsigned int bit; struct gpio_bank *bank = gpiobank; - unsigned long wa_lock_flags; - unsigned long lock_flags;
isr_reg = bank->base + bank->regs->irqstatus; if (WARN_ON(!isr_reg)) @@ -572,7 +570,7 @@ static irqreturn_t omap_gpio_irq_handler(int irq, void *gpiobank) return IRQ_NONE;
while (1) { - raw_spin_lock_irqsave(&bank->lock, lock_flags); + raw_spin_lock(&bank->lock);
enabled = omap_get_gpio_irqbank_mask(bank); isr = readl_relaxed(isr_reg) & enabled; @@ -586,7 +584,7 @@ static irqreturn_t omap_gpio_irq_handler(int irq, void *gpiobank) if (edge) omap_clear_gpio_irqbank(bank, edge);
- raw_spin_unlock_irqrestore(&bank->lock, lock_flags); + raw_spin_unlock(&bank->lock);
if (!isr) break; @@ -595,7 +593,7 @@ static irqreturn_t omap_gpio_irq_handler(int irq, void *gpiobank) bit = __ffs(isr); isr &= ~(BIT(bit));
- raw_spin_lock_irqsave(&bank->lock, lock_flags); + raw_spin_lock(&bank->lock); /* * Some chips can't respond to both rising and falling * at the same time. If this irq was requested with @@ -606,15 +604,14 @@ static irqreturn_t omap_gpio_irq_handler(int irq, void *gpiobank) if (bank->toggle_mask & (BIT(bit))) omap_toggle_gpio_edge_triggering(bank, bit);
- raw_spin_unlock_irqrestore(&bank->lock, lock_flags); + raw_spin_unlock(&bank->lock);
- raw_spin_lock_irqsave(&bank->wa_lock, wa_lock_flags); + raw_spin_lock(&bank->wa_lock);
generic_handle_irq(irq_find_mapping(bank->chip.irq.domain, bit));
- raw_spin_unlock_irqrestore(&bank->wa_lock, - wa_lock_flags); + raw_spin_unlock(&bank->wa_lock); } } exit:
On 08/02/2021 10:56, Luo Jiaxing wrote:
There is no need to use API with _irqsave in omap_gpio_irq_handler(), because it already be in a irq-disabled context.
Signed-off-by: Luo Jiaxing luojiaxing@huawei.com
drivers/gpio/gpio-omap.c | 15 ++++++--------- 1 file changed, 6 insertions(+), 9 deletions(-)
diff --git a/drivers/gpio/gpio-omap.c b/drivers/gpio/gpio-omap.c index 41952bb..dc8bbf4 100644 --- a/drivers/gpio/gpio-omap.c +++ b/drivers/gpio/gpio-omap.c @@ -560,8 +560,6 @@ static irqreturn_t omap_gpio_irq_handler(int irq, void *gpiobank) u32 enabled, isr, edge; unsigned int bit; struct gpio_bank *bank = gpiobank;
unsigned long wa_lock_flags;
unsigned long lock_flags;
isr_reg = bank->base + bank->regs->irqstatus; if (WARN_ON(!isr_reg))
@@ -572,7 +570,7 @@ static irqreturn_t omap_gpio_irq_handler(int irq, void *gpiobank) return IRQ_NONE;
while (1) {
raw_spin_lock_irqsave(&bank->lock, lock_flags);
raw_spin_lock(&bank->lock);enabled = omap_get_gpio_irqbank_mask(bank); isr = readl_relaxed(isr_reg) & enabled;
@@ -586,7 +584,7 @@ static irqreturn_t omap_gpio_irq_handler(int irq, void *gpiobank) if (edge) omap_clear_gpio_irqbank(bank, edge);
raw_spin_unlock_irqrestore(&bank->lock, lock_flags);
raw_spin_unlock(&bank->lock);if (!isr) break;
@@ -595,7 +593,7 @@ static irqreturn_t omap_gpio_irq_handler(int irq, void *gpiobank) bit = __ffs(isr); isr &= ~(BIT(bit));
raw_spin_lock_irqsave(&bank->lock, lock_flags);
raw_spin_lock(&bank->lock); /* * Some chips can't respond to both rising and falling * at the same time. If this irq was requested with@@ -606,15 +604,14 @@ static irqreturn_t omap_gpio_irq_handler(int irq, void *gpiobank) if (bank->toggle_mask & (BIT(bit))) omap_toggle_gpio_edge_triggering(bank, bit);
raw_spin_unlock_irqrestore(&bank->lock, lock_flags);
raw_spin_unlock(&bank->lock);
raw_spin_lock_irqsave(&bank->wa_lock, wa_lock_flags);
raw_spin_lock(&bank->wa_lock); generic_handle_irq(irq_find_mapping(bank->chip.irq.domain, bit));
raw_spin_unlock_irqrestore(&bank->wa_lock,wa_lock_flags);
raw_spin_unlock(&bank->wa_lock);
NACK. Who said that this is always hard IRQ handler? What about RT-kernel or boot with "threadirqs"?
On Thu, Feb 11, 2021 at 7:25 PM Grygorii Strashko grygorii.strashko@ti.com wrote:
On 08/02/2021 10:56, Luo Jiaxing wrote:
There is no need to use API with _irqsave in omap_gpio_irq_handler(), because it already be in a irq-disabled context.
NACK. Who said that this is always hard IRQ handler? What about RT-kernel or boot with "threadirqs"?
In those cases, the interrupt handler is just a normal thread, so the preempt_disable() that is implied by raw_spin_lock() is sufficient.
Disabling interrupts inside of an interrupt handler is always incorrect, the patch looks like a useful cleanup to me, if only for readability.
Arnd
On 11/02/2021 21:39, Arnd Bergmann wrote:
On Thu, Feb 11, 2021 at 7:25 PM Grygorii Strashko grygorii.strashko@ti.com wrote:
On 08/02/2021 10:56, Luo Jiaxing wrote:
There is no need to use API with _irqsave in omap_gpio_irq_handler(), because it already be in a irq-disabled context.
NACK. Who said that this is always hard IRQ handler? What about RT-kernel or boot with "threadirqs"?
In those cases, the interrupt handler is just a normal thread, so the preempt_disable() that is implied by raw_spin_lock() is sufficient.
Disabling interrupts inside of an interrupt handler is always incorrect, the patch looks like a useful cleanup to me, if only for readability.
Note. there is also generic_handle_irq() call inside.
-----Original Message----- From: Grygorii Strashko [mailto:grygorii.strashko@ti.com] Sent: Friday, February 12, 2021 9:17 AM To: Arnd Bergmann arnd@kernel.org Cc: luojiaxing luojiaxing@huawei.com; Linus Walleij linus.walleij@linaro.org; Andy Shevchenko andy.shevchenko@gmail.com; Andy Shevchenko andriy.shevchenko@linux.intel.com; Santosh Shilimkar ssantosh@kernel.org; Kevin Hilman khilman@kernel.org; open list:GPIO SUBSYSTEM linux-gpio@vger.kernel.org, linux-kernel@vger.kernel.org linux-kernel@vger.kernel.org; linuxarm@openeuler.org Subject: [Linuxarm] Re: [PATCH for next v1 1/2] gpio: omap: Replace raw_spin_lock_irqsave with raw_spin_lock in omap_gpio_irq_handler()
On 11/02/2021 21:39, Arnd Bergmann wrote:
On Thu, Feb 11, 2021 at 7:25 PM Grygorii Strashko grygorii.strashko@ti.com wrote:
On 08/02/2021 10:56, Luo Jiaxing wrote:
There is no need to use API with _irqsave in omap_gpio_irq_handler(), because it already be in a irq-disabled context.
NACK. Who said that this is always hard IRQ handler? What about RT-kernel or boot with "threadirqs"?
In those cases, the interrupt handler is just a normal thread, so the preempt_disable() that is implied by raw_spin_lock() is sufficient.
Disabling interrupts inside of an interrupt handler is always incorrect, the patch looks like a useful cleanup to me, if only for readability.
Note. there is also generic_handle_irq() call inside.
So generic_handle_irq() is not safe to run in thread thus requires an interrupt-disabled environment to run? If so, I'd rather this irqsave moved into generic_handle_irq() rather than asking everyone calling it to do irqsave.
On the other hand, the author changed a couple of spin_lock_irqsave to spin_lock, if only this one is incorrect, it seems it is worth a new version to fix this.
-- Best regards, grygorii
Thanks Barry
On Fri, Feb 12, 2021 at 6:05 AM Song Bao Hua (Barry Song) song.bao.hua@hisilicon.com wrote:
-----Original Message-----
Note. there is also generic_handle_irq() call inside.
So generic_handle_irq() is not safe to run in thread thus requires an interrupt-disabled environment to run? If so, I'd rather this irqsave moved into generic_handle_irq() rather than asking everyone calling it to do irqsave.
In a preempt-rt kernel, interrupts are run in task context, so they clearly should not be called with interrupts disabled, that would defeat the purpose of making them preemptible.
generic_handle_irq() does need to run with in_irq()==true though, but this should be set by the caller of the gpiochip's handler, and it is not set by raw_spin_lock_irqsave().
Arnd
-----Original Message----- From: Arnd Bergmann [mailto:arnd@kernel.org] Sent: Friday, February 12, 2021 10:45 PM To: Song Bao Hua (Barry Song) song.bao.hua@hisilicon.com Cc: Grygorii Strashko grygorii.strashko@ti.com; luojiaxing luojiaxing@huawei.com; Linus Walleij linus.walleij@linaro.org; Andy Shevchenko andy.shevchenko@gmail.com; Andy Shevchenko andriy.shevchenko@linux.intel.com; Santosh Shilimkar ssantosh@kernel.org; Kevin Hilman khilman@kernel.org; open list:GPIO SUBSYSTEM linux-gpio@vger.kernel.org, linux-kernel@vger.kernel.org linux-kernel@vger.kernel.org; linuxarm@openeuler.org Subject: Re: [Linuxarm] Re: [PATCH for next v1 1/2] gpio: omap: Replace raw_spin_lock_irqsave with raw_spin_lock in omap_gpio_irq_handler()
On Fri, Feb 12, 2021 at 6:05 AM Song Bao Hua (Barry Song) song.bao.hua@hisilicon.com wrote:
-----Original Message-----
Note. there is also generic_handle_irq() call inside.
So generic_handle_irq() is not safe to run in thread thus requires an interrupt-disabled environment to run? If so, I'd rather this irqsave moved into generic_handle_irq() rather than asking everyone calling it to do irqsave.
In a preempt-rt kernel, interrupts are run in task context, so they clearly should not be called with interrupts disabled, that would defeat the purpose of making them preemptible.
Yes. Sounds sensible. Irqsave in generic_handle_irq() will defeat the purpose of RT.
generic_handle_irq() does need to run with in_irq()==true though, but this should be set by the caller of the gpiochip's handler, and it is not set by raw_spin_lock_irqsave().
So sounds like this issue of in_irq()=true is still irrelevant with this patch.
I guess this should have been set by the caller of the gpiochip's handler somewhere, otherwise, gpiochip's irq handler won't be able to be threaded. Has it been set somewhere?
Arnd
Thanks Barry
Hi Arnd,
On 12/02/2021 11:45, Arnd Bergmann wrote:
On Fri, Feb 12, 2021 at 6:05 AM Song Bao Hua (Barry Song) song.bao.hua@hisilicon.com wrote:
-----Original Message-----
Note. there is also generic_handle_irq() call inside.
So generic_handle_irq() is not safe to run in thread thus requires an interrupt-disabled environment to run? If so, I'd rather this irqsave moved into generic_handle_irq() rather than asking everyone calling it to do irqsave.
In a preempt-rt kernel, interrupts are run in task context, so they clearly should not be called with interrupts disabled, that would defeat the purpose of making them preemptible.
generic_handle_irq() does need to run with in_irq()==true though, but this should be set by the caller of the gpiochip's handler, and it is not set by raw_spin_lock_irqsave().
It will produce warning from __handle_irq_event_percpu(), as this is IRQ dispatcher and generic_handle_irq() will call one of handle_level_irq or handle_edge_irq.
The history behind this is commit 450fa54cfd66 ("gpio: omap: convert to use generic irq handler").
The resent related discussion: https://lkml.org/lkml/2020/12/5/208
-----Original Message----- From: Grygorii Strashko [mailto:grygorii.strashko@ti.com] Sent: Friday, February 12, 2021 11:28 PM To: Arnd Bergmann arnd@kernel.org; Song Bao Hua (Barry Song) song.bao.hua@hisilicon.com Cc: luojiaxing luojiaxing@huawei.com; Linus Walleij linus.walleij@linaro.org; Andy Shevchenko andy.shevchenko@gmail.com; Andy Shevchenko andriy.shevchenko@linux.intel.com; Santosh Shilimkar ssantosh@kernel.org; Kevin Hilman khilman@kernel.org; open list:GPIO SUBSYSTEM linux-gpio@vger.kernel.org; linux-kernel@vger.kernel.org; linuxarm@openeuler.org Subject: Re: [Linuxarm] Re: [PATCH for next v1 1/2] gpio: omap: Replace raw_spin_lock_irqsave with raw_spin_lock in omap_gpio_irq_handler()
Hi Arnd,
On 12/02/2021 11:45, Arnd Bergmann wrote:
On Fri, Feb 12, 2021 at 6:05 AM Song Bao Hua (Barry Song) song.bao.hua@hisilicon.com wrote:
-----Original Message-----
Note. there is also generic_handle_irq() call inside.
So generic_handle_irq() is not safe to run in thread thus requires an interrupt-disabled environment to run? If so, I'd rather this irqsave moved into generic_handle_irq() rather than asking everyone calling it to do irqsave.
In a preempt-rt kernel, interrupts are run in task context, so they clearly should not be called with interrupts disabled, that would defeat the purpose of making them preemptible.
generic_handle_irq() does need to run with in_irq()==true though, but this should be set by the caller of the gpiochip's handler, and it is not set by raw_spin_lock_irqsave().
It will produce warning from __handle_irq_event_percpu(), as this is IRQ dispatcher and generic_handle_irq() will call one of handle_level_irq or handle_edge_irq.
The history behind this is commit 450fa54cfd66 ("gpio: omap: convert to use generic irq handler").
The resent related discussion: https://lkml.org/lkml/2020/12/5/208
Ok, second thought. irqsave before generic_handle_irq() won't defeat the purpose of preemption too much as the dispatched irq handlers by gpiochip will run in their own threads but not in the thread of gpiochip's handler.
so looks like this patch can improve by: * move other raw_spin_lock_irqsave to raw_spin_lock; * keep the raw_spin_lock_irqsave before generic_handle_irq() to mute the warning in genirq.
-- Best regards, Grygorii
Thanks Barry
On Fri, Feb 12, 2021 at 10:42:19AM +0000, Song Bao Hua (Barry Song) wrote:
From: Grygorii Strashko [mailto:grygorii.strashko@ti.com] Sent: Friday, February 12, 2021 11:28 PM On 12/02/2021 11:45, Arnd Bergmann wrote:
On Fri, Feb 12, 2021 at 6:05 AM Song Bao Hua (Barry Song) song.bao.hua@hisilicon.com wrote:
Note. there is also generic_handle_irq() call inside.
So generic_handle_irq() is not safe to run in thread thus requires an interrupt-disabled environment to run? If so, I'd rather this irqsave moved into generic_handle_irq() rather than asking everyone calling it to do irqsave.
In a preempt-rt kernel, interrupts are run in task context, so they clearly should not be called with interrupts disabled, that would defeat the purpose of making them preemptible.
generic_handle_irq() does need to run with in_irq()==true though, but this should be set by the caller of the gpiochip's handler, and it is not set by raw_spin_lock_irqsave().
It will produce warning from __handle_irq_event_percpu(), as this is IRQ dispatcher and generic_handle_irq() will call one of handle_level_irq or handle_edge_irq.
The history behind this is commit 450fa54cfd66 ("gpio: omap: convert to use generic irq handler").
The resent related discussion: https://lkml.org/lkml/2020/12/5/208
Ok, second thought. irqsave before generic_handle_irq() won't defeat the purpose of preemption too much as the dispatched irq handlers by gpiochip will run in their own threads but not in the thread of gpiochip's handler.
so looks like this patch can improve by:
- move other raw_spin_lock_irqsave to raw_spin_lock;
- keep the raw_spin_lock_irqsave before generic_handle_irq() to mute
the warning in genirq.
Isn't the idea of irqsave is to prevent dead lock from the process context when we get interrupt on the *same* CPU?
-----Original Message----- From: Andy Shevchenko [mailto:andy.shevchenko@gmail.com] Sent: Friday, February 12, 2021 11:57 PM To: Song Bao Hua (Barry Song) song.bao.hua@hisilicon.com Cc: Grygorii Strashko grygorii.strashko@ti.com; Arnd Bergmann arnd@kernel.org; luojiaxing luojiaxing@huawei.com; Linus Walleij linus.walleij@linaro.org; Santosh Shilimkar ssantosh@kernel.org; Kevin Hilman khilman@kernel.org; open list:GPIO SUBSYSTEM linux-gpio@vger.kernel.org; linux-kernel@vger.kernel.org; linuxarm@openeuler.org Subject: Re: [Linuxarm] Re: [PATCH for next v1 1/2] gpio: omap: Replace raw_spin_lock_irqsave with raw_spin_lock in omap_gpio_irq_handler()
On Fri, Feb 12, 2021 at 10:42:19AM +0000, Song Bao Hua (Barry Song) wrote:
From: Grygorii Strashko [mailto:grygorii.strashko@ti.com] Sent: Friday, February 12, 2021 11:28 PM On 12/02/2021 11:45, Arnd Bergmann wrote:
On Fri, Feb 12, 2021 at 6:05 AM Song Bao Hua (Barry Song) song.bao.hua@hisilicon.com wrote:
Note. there is also generic_handle_irq() call inside.
So generic_handle_irq() is not safe to run in thread thus requires an interrupt-disabled environment to run? If so, I'd rather this irqsave moved into generic_handle_irq() rather than asking everyone calling it to do irqsave.
In a preempt-rt kernel, interrupts are run in task context, so they clearly should not be called with interrupts disabled, that would defeat the purpose of making them preemptible.
generic_handle_irq() does need to run with in_irq()==true though, but this should be set by the caller of the gpiochip's handler, and it is not set by raw_spin_lock_irqsave().
It will produce warning from __handle_irq_event_percpu(), as this is IRQ dispatcher and generic_handle_irq() will call one of handle_level_irq or
handle_edge_irq.
The history behind this is commit 450fa54cfd66 ("gpio: omap: convert to
use
generic irq handler").
The resent related discussion: https://lkml.org/lkml/2020/12/5/208
Ok, second thought. irqsave before generic_handle_irq() won't defeat the purpose of preemption too much as the dispatched irq handlers by gpiochip will run in their own threads but not in the thread of gpiochip's handler.
so looks like this patch can improve by:
- move other raw_spin_lock_irqsave to raw_spin_lock;
- keep the raw_spin_lock_irqsave before generic_handle_irq() to mute
the warning in genirq.
Isn't the idea of irqsave is to prevent dead lock from the process context when we get interrupt on the *same* CPU?
Anyway, gpiochip is more tricky as it is also a irq dispatcher. Moving spin_lock_irq to spin_lock in the irq handler of non-irq dispatcher driver is almost always correct.
But for gpiochip, would the below be true though it is almost alway true for non-irq dispatcher?
1. While gpiochip's handler runs in hardIRQ, interrupts are disabled, so no more interrupt on the same cpu -> No deadleak.
2. While gpiochip's handler runs in threads * other non-threaded interrupts such as timer tick might come on same cpu, but they are an irrelevant driver and thus they are not going to get the lock gpiochip's handler has held. -> no deadlock. * other devices attached to this gpiochip might get interrupts, since gpiochip's handler is running in threads, raw_spin_lock can help avoid messing up the critical data by two threads -> still no deadlock.
-- With Best Regards, Andy Shevchenko
Thanks Barry
On 12/02/2021 13:29, Song Bao Hua (Barry Song) wrote:
-----Original Message----- From: Andy Shevchenko [mailto:andy.shevchenko@gmail.com] Sent: Friday, February 12, 2021 11:57 PM To: Song Bao Hua (Barry Song) song.bao.hua@hisilicon.com Cc: Grygorii Strashko grygorii.strashko@ti.com; Arnd Bergmann arnd@kernel.org; luojiaxing luojiaxing@huawei.com; Linus Walleij linus.walleij@linaro.org; Santosh Shilimkar ssantosh@kernel.org; Kevin Hilman khilman@kernel.org; open list:GPIO SUBSYSTEM linux-gpio@vger.kernel.org; linux-kernel@vger.kernel.org; linuxarm@openeuler.org Subject: Re: [Linuxarm] Re: [PATCH for next v1 1/2] gpio: omap: Replace raw_spin_lock_irqsave with raw_spin_lock in omap_gpio_irq_handler()
On Fri, Feb 12, 2021 at 10:42:19AM +0000, Song Bao Hua (Barry Song) wrote:
From: Grygorii Strashko [mailto:grygorii.strashko@ti.com] Sent: Friday, February 12, 2021 11:28 PM On 12/02/2021 11:45, Arnd Bergmann wrote:
On Fri, Feb 12, 2021 at 6:05 AM Song Bao Hua (Barry Song) song.bao.hua@hisilicon.com wrote:
> Note. there is also generic_handle_irq() call inside.
So generic_handle_irq() is not safe to run in thread thus requires an interrupt-disabled environment to run? If so, I'd rather this irqsave moved into generic_handle_irq() rather than asking everyone calling it to do irqsave.
In a preempt-rt kernel, interrupts are run in task context, so they clearly should not be called with interrupts disabled, that would defeat the purpose of making them preemptible.
generic_handle_irq() does need to run with in_irq()==true though, but this should be set by the caller of the gpiochip's handler, and it is not set by raw_spin_lock_irqsave().
It will produce warning from __handle_irq_event_percpu(), as this is IRQ dispatcher and generic_handle_irq() will call one of handle_level_irq or
handle_edge_irq.
The history behind this is commit 450fa54cfd66 ("gpio: omap: convert to
use
generic irq handler").
The resent related discussion: https://lkml.org/lkml/2020/12/5/208
Ok, second thought. irqsave before generic_handle_irq() won't defeat the purpose of preemption too much as the dispatched irq handlers by gpiochip will run in their own threads but not in the thread of gpiochip's handler.
so looks like this patch can improve by:
- move other raw_spin_lock_irqsave to raw_spin_lock;
- keep the raw_spin_lock_irqsave before generic_handle_irq() to mute
the warning in genirq.
Isn't the idea of irqsave is to prevent dead lock from the process context when we get interrupt on the *same* CPU?
Anyway, gpiochip is more tricky as it is also a irq dispatcher. Moving spin_lock_irq to spin_lock in the irq handler of non-irq dispatcher driver is almost always correct.
But for gpiochip, would the below be true though it is almost alway true for non-irq dispatcher?
- While gpiochip's handler runs in hardIRQ, interrupts are disabled, so no more
interrupt on the same cpu -> No deadleak.
- While gpiochip's handler runs in threads
- other non-threaded interrupts such as timer tick might come on same cpu,
but they are an irrelevant driver and thus they are not going to get the lock gpiochip's handler has held. -> no deadlock.
- other devices attached to this gpiochip might get interrupts, since
gpiochip's handler is running in threads, raw_spin_lock can help avoid messing up the critical data by two threads -> still no deadlock.
The worst RT case I can imagine is when gpio API is still called from hard IRQ context by some other device driver - some toggling for example. Note. RT or "threadirqs" does not mean gpiochip become sleepable.
In this case: threaded handler raw_spin_lock IRQ from other device hard_irq handler gpiod_x() raw_spin_lock_irqsave() -- oops
But in general, what are the benefit of such changes at all, except better marking call context annotation, so we are spending so much time on it?
-----Original Message----- From: Grygorii Strashko [mailto:grygorii.strashko@ti.com] Sent: Saturday, February 13, 2021 12:53 AM To: Song Bao Hua (Barry Song) song.bao.hua@hisilicon.com; Andy Shevchenko andy.shevchenko@gmail.com Cc: Arnd Bergmann arnd@kernel.org; luojiaxing luojiaxing@huawei.com; Linus Walleij linus.walleij@linaro.org; Santosh Shilimkar ssantosh@kernel.org; Kevin Hilman khilman@kernel.org; open list:GPIO SUBSYSTEM linux-gpio@vger.kernel.org; linux-kernel@vger.kernel.org; linuxarm@openeuler.org Subject: Re: [Linuxarm] Re: [PATCH for next v1 1/2] gpio: omap: Replace raw_spin_lock_irqsave with raw_spin_lock in omap_gpio_irq_handler()
On 12/02/2021 13:29, Song Bao Hua (Barry Song) wrote:
-----Original Message----- From: Andy Shevchenko [mailto:andy.shevchenko@gmail.com] Sent: Friday, February 12, 2021 11:57 PM To: Song Bao Hua (Barry Song) song.bao.hua@hisilicon.com Cc: Grygorii Strashko grygorii.strashko@ti.com; Arnd Bergmann arnd@kernel.org; luojiaxing luojiaxing@huawei.com; Linus Walleij linus.walleij@linaro.org; Santosh Shilimkar ssantosh@kernel.org; Kevin Hilman khilman@kernel.org; open list:GPIO SUBSYSTEM linux-gpio@vger.kernel.org; linux-kernel@vger.kernel.org; linuxarm@openeuler.org Subject: Re: [Linuxarm] Re: [PATCH for next v1 1/2] gpio: omap: Replace raw_spin_lock_irqsave with raw_spin_lock in omap_gpio_irq_handler()
On Fri, Feb 12, 2021 at 10:42:19AM +0000, Song Bao Hua (Barry Song) wrote:
From: Grygorii Strashko [mailto:grygorii.strashko@ti.com] Sent: Friday, February 12, 2021 11:28 PM On 12/02/2021 11:45, Arnd Bergmann wrote:
On Fri, Feb 12, 2021 at 6:05 AM Song Bao Hua (Barry Song) song.bao.hua@hisilicon.com wrote:
>> Note. there is also generic_handle_irq() call inside. > > So generic_handle_irq() is not safe to run in thread thus requires > an interrupt-disabled environment to run? If so, I'd rather this > irqsave moved into generic_handle_irq() rather than asking everyone > calling it to do irqsave.
In a preempt-rt kernel, interrupts are run in task context, so they clearly should not be called with interrupts disabled, that would defeat the purpose of making them preemptible.
generic_handle_irq() does need to run with in_irq()==true though, but this should be set by the caller of the gpiochip's handler, and it is not set by raw_spin_lock_irqsave().
It will produce warning from __handle_irq_event_percpu(), as this is IRQ dispatcher and generic_handle_irq() will call one of handle_level_irq or
handle_edge_irq.
The history behind this is commit 450fa54cfd66 ("gpio: omap: convert to
use
generic irq handler").
The resent related discussion: https://lkml.org/lkml/2020/12/5/208
Ok, second thought. irqsave before generic_handle_irq() won't defeat the purpose of preemption too much as the dispatched irq handlers by gpiochip will run in their own threads but not in the thread of gpiochip's handler.
so looks like this patch can improve by:
- move other raw_spin_lock_irqsave to raw_spin_lock;
- keep the raw_spin_lock_irqsave before generic_handle_irq() to mute
the warning in genirq.
Isn't the idea of irqsave is to prevent dead lock from the process context
when
we get interrupt on the *same* CPU?
Anyway, gpiochip is more tricky as it is also a irq dispatcher. Moving spin_lock_irq to spin_lock in the irq handler of non-irq dispatcher driver is almost always correct.
But for gpiochip, would the below be true though it is almost alway true for non-irq dispatcher?
- While gpiochip's handler runs in hardIRQ, interrupts are disabled, so no
more
interrupt on the same cpu -> No deadleak.
- While gpiochip's handler runs in threads
- other non-threaded interrupts such as timer tick might come on same cpu,
but they are an irrelevant driver and thus they are not going to get the lock gpiochip's handler has held. -> no deadlock.
- other devices attached to this gpiochip might get interrupts, since
gpiochip's handler is running in threads, raw_spin_lock can help avoid messing up the critical data by two threads -> still no deadlock.
The worst RT case I can imagine is when gpio API is still called from hard IRQ context by some other device driver - some toggling for example. Note. RT or "threadirqs" does not mean gpiochip become sleepable.
In this case: threaded handler raw_spin_lock IRQ from other device hard_irq handler gpiod_x() raw_spin_lock_irqsave() -- oops
Actually no oops here. other drivers don't hold the same spinlock of this driver.
But in general, what are the benefit of such changes at all, except better marking call context annotation, so we are spending so much time on it?
TBH, the benefit is really tiny except code cleanup. just curious how things could be different while it happens in an irq dispatcher's handler.
-- Best regards, Grygorii
Thanks Barry
On 12/02/2021 15:12, Song Bao Hua (Barry Song) wrote:
-----Original Message----- From: Grygorii Strashko [mailto:grygorii.strashko@ti.com] Sent: Saturday, February 13, 2021 12:53 AM To: Song Bao Hua (Barry Song) song.bao.hua@hisilicon.com; Andy Shevchenko andy.shevchenko@gmail.com Cc: Arnd Bergmann arnd@kernel.org; luojiaxing luojiaxing@huawei.com; Linus Walleij linus.walleij@linaro.org; Santosh Shilimkar ssantosh@kernel.org; Kevin Hilman khilman@kernel.org; open list:GPIO SUBSYSTEM linux-gpio@vger.kernel.org; linux-kernel@vger.kernel.org; linuxarm@openeuler.org Subject: Re: [Linuxarm] Re: [PATCH for next v1 1/2] gpio: omap: Replace raw_spin_lock_irqsave with raw_spin_lock in omap_gpio_irq_handler()
On 12/02/2021 13:29, Song Bao Hua (Barry Song) wrote:
-----Original Message----- From: Andy Shevchenko [mailto:andy.shevchenko@gmail.com] Sent: Friday, February 12, 2021 11:57 PM To: Song Bao Hua (Barry Song) song.bao.hua@hisilicon.com Cc: Grygorii Strashko grygorii.strashko@ti.com; Arnd Bergmann arnd@kernel.org; luojiaxing luojiaxing@huawei.com; Linus Walleij linus.walleij@linaro.org; Santosh Shilimkar ssantosh@kernel.org; Kevin Hilman khilman@kernel.org; open list:GPIO SUBSYSTEM linux-gpio@vger.kernel.org; linux-kernel@vger.kernel.org; linuxarm@openeuler.org Subject: Re: [Linuxarm] Re: [PATCH for next v1 1/2] gpio: omap: Replace raw_spin_lock_irqsave with raw_spin_lock in omap_gpio_irq_handler()
On Fri, Feb 12, 2021 at 10:42:19AM +0000, Song Bao Hua (Barry Song) wrote:
From: Grygorii Strashko [mailto:grygorii.strashko@ti.com] Sent: Friday, February 12, 2021 11:28 PM On 12/02/2021 11:45, Arnd Bergmann wrote: > On Fri, Feb 12, 2021 at 6:05 AM Song Bao Hua (Barry Song) > song.bao.hua@hisilicon.com wrote:
>>> Note. there is also generic_handle_irq() call inside. >> >> So generic_handle_irq() is not safe to run in thread thus requires >> an interrupt-disabled environment to run? If so, I'd rather this >> irqsave moved into generic_handle_irq() rather than asking everyone >> calling it to do irqsave. > > In a preempt-rt kernel, interrupts are run in task context, so they clearly > should not be called with interrupts disabled, that would defeat the > purpose of making them preemptible. > > generic_handle_irq() does need to run with in_irq()==true though, > but this should be set by the caller of the gpiochip's handler, and > it is not set by raw_spin_lock_irqsave().
It will produce warning from __handle_irq_event_percpu(), as this is IRQ dispatcher and generic_handle_irq() will call one of handle_level_irq or
handle_edge_irq.
The history behind this is commit 450fa54cfd66 ("gpio: omap: convert to
use
generic irq handler").
The resent related discussion: https://lkml.org/lkml/2020/12/5/208
Ok, second thought. irqsave before generic_handle_irq() won't defeat the purpose of preemption too much as the dispatched irq handlers by gpiochip will run in their own threads but not in the thread of gpiochip's handler.
so looks like this patch can improve by:
- move other raw_spin_lock_irqsave to raw_spin_lock;
- keep the raw_spin_lock_irqsave before generic_handle_irq() to mute
the warning in genirq.
Isn't the idea of irqsave is to prevent dead lock from the process context
when
we get interrupt on the *same* CPU?
Anyway, gpiochip is more tricky as it is also a irq dispatcher. Moving spin_lock_irq to spin_lock in the irq handler of non-irq dispatcher driver is almost always correct.
But for gpiochip, would the below be true though it is almost alway true for non-irq dispatcher?
- While gpiochip's handler runs in hardIRQ, interrupts are disabled, so no
more
interrupt on the same cpu -> No deadleak.
- While gpiochip's handler runs in threads
- other non-threaded interrupts such as timer tick might come on same cpu,
but they are an irrelevant driver and thus they are not going to get the lock gpiochip's handler has held. -> no deadlock.
- other devices attached to this gpiochip might get interrupts, since
gpiochip's handler is running in threads, raw_spin_lock can help avoid messing up the critical data by two threads -> still no deadlock.
The worst RT case I can imagine is when gpio API is still called from hard IRQ context by some other device driver - some toggling for example. Note. RT or "threadirqs" does not mean gpiochip become sleepable.
In this case: threaded handler raw_spin_lock IRQ from other device hard_irq handler gpiod_x() raw_spin_lock_irqsave() -- oops
Actually no oops here. other drivers don't hold the same spinlock of this driver.
huh. driver/module A requests gpio and uses it in its hard_irq handler by calling GPIO API (Like gpiod_set_value()), those will go to this driver and end up in omap_gpio_set().
But in general, what are the benefit of such changes at all, except better marking call context annotation, so we are spending so much time on it?
TBH, the benefit is really tiny except code cleanup. just curious how things could be different while it happens in an irq dispatcher's handler.
-----Original Message----- From: Grygorii Strashko [mailto:grygorii.strashko@ti.com] Sent: Saturday, February 13, 2021 3:09 AM To: Song Bao Hua (Barry Song) song.bao.hua@hisilicon.com; Andy Shevchenko andy.shevchenko@gmail.com Cc: Arnd Bergmann arnd@kernel.org; luojiaxing luojiaxing@huawei.com; Linus Walleij linus.walleij@linaro.org; Santosh Shilimkar ssantosh@kernel.org; Kevin Hilman khilman@kernel.org; open list:GPIO SUBSYSTEM linux-gpio@vger.kernel.org; linux-kernel@vger.kernel.org; linuxarm@openeuler.org Subject: Re: [Linuxarm] Re: [PATCH for next v1 1/2] gpio: omap: Replace raw_spin_lock_irqsave with raw_spin_lock in omap_gpio_irq_handler()
On 12/02/2021 15:12, Song Bao Hua (Barry Song) wrote:
-----Original Message----- From: Grygorii Strashko [mailto:grygorii.strashko@ti.com] Sent: Saturday, February 13, 2021 12:53 AM To: Song Bao Hua (Barry Song) song.bao.hua@hisilicon.com; Andy Shevchenko andy.shevchenko@gmail.com Cc: Arnd Bergmann arnd@kernel.org; luojiaxing luojiaxing@huawei.com;
Linus
Walleij linus.walleij@linaro.org; Santosh Shilimkar
Kevin Hilman khilman@kernel.org; open list:GPIO SUBSYSTEM linux-gpio@vger.kernel.org; linux-kernel@vger.kernel.org; linuxarm@openeuler.org Subject: Re: [Linuxarm] Re: [PATCH for next v1 1/2] gpio: omap: Replace raw_spin_lock_irqsave with raw_spin_lock in omap_gpio_irq_handler()
On 12/02/2021 13:29, Song Bao Hua (Barry Song) wrote:
-----Original Message----- From: Andy Shevchenko [mailto:andy.shevchenko@gmail.com] Sent: Friday, February 12, 2021 11:57 PM To: Song Bao Hua (Barry Song) song.bao.hua@hisilicon.com Cc: Grygorii Strashko grygorii.strashko@ti.com; Arnd Bergmann arnd@kernel.org; luojiaxing luojiaxing@huawei.com; Linus Walleij linus.walleij@linaro.org; Santosh Shilimkar ssantosh@kernel.org;
Kevin
Hilman khilman@kernel.org; open list:GPIO SUBSYSTEM linux-gpio@vger.kernel.org; linux-kernel@vger.kernel.org; linuxarm@openeuler.org Subject: Re: [Linuxarm] Re: [PATCH for next v1 1/2] gpio: omap: Replace raw_spin_lock_irqsave with raw_spin_lock in omap_gpio_irq_handler()
On Fri, Feb 12, 2021 at 10:42:19AM +0000, Song Bao Hua (Barry Song) wrote:
> From: Grygorii Strashko [mailto:grygorii.strashko@ti.com] > Sent: Friday, February 12, 2021 11:28 PM > On 12/02/2021 11:45, Arnd Bergmann wrote: >> On Fri, Feb 12, 2021 at 6:05 AM Song Bao Hua (Barry Song) >> song.bao.hua@hisilicon.com wrote:
>>>> Note. there is also generic_handle_irq() call inside. >>> >>> So generic_handle_irq() is not safe to run in thread thus requires >>> an interrupt-disabled environment to run? If so, I'd rather this >>> irqsave moved into generic_handle_irq() rather than asking everyone >>> calling it to do irqsave. >> >> In a preempt-rt kernel, interrupts are run in task context, so they
clearly
>> should not be called with interrupts disabled, that would defeat the >> purpose of making them preemptible. >> >> generic_handle_irq() does need to run with in_irq()==true though, >> but this should be set by the caller of the gpiochip's handler, and >> it is not set by raw_spin_lock_irqsave(). > > It will produce warning from __handle_irq_event_percpu(), as this is
IRQ
> dispatcher > and generic_handle_irq() will call one of handle_level_irq or
handle_edge_irq.
> > The history behind this is commit 450fa54cfd66 ("gpio: omap: convert
to
use
> generic irq handler"). > > The resent related discussion: > https://lkml.org/lkml/2020/12/5/208
Ok, second thought. irqsave before generic_handle_irq() won't defeat the purpose of preemption too much as the dispatched irq handlers by gpiochip will run in their own threads but not in the thread of gpiochip's handler.
so looks like this patch can improve by:
- move other raw_spin_lock_irqsave to raw_spin_lock;
- keep the raw_spin_lock_irqsave before generic_handle_irq() to mute
the warning in genirq.
Isn't the idea of irqsave is to prevent dead lock from the process context
when
we get interrupt on the *same* CPU?
Anyway, gpiochip is more tricky as it is also a irq dispatcher. Moving spin_lock_irq to spin_lock in the irq handler of non-irq dispatcher driver is almost always correct.
But for gpiochip, would the below be true though it is almost alway true for non-irq dispatcher?
- While gpiochip's handler runs in hardIRQ, interrupts are disabled, so
no
more
interrupt on the same cpu -> No deadleak.
- While gpiochip's handler runs in threads
- other non-threaded interrupts such as timer tick might come on same cpu,
but they are an irrelevant driver and thus they are not going to get the lock gpiochip's handler has held. -> no deadlock.
- other devices attached to this gpiochip might get interrupts, since
gpiochip's handler is running in threads, raw_spin_lock can help avoid messing up the critical data by two threads -> still no deadlock.
The worst RT case I can imagine is when gpio API is still called from hard
IRQ
context by some other device driver - some toggling for example. Note. RT or "threadirqs" does not mean gpiochip become sleepable.
In this case: threaded handler raw_spin_lock IRQ from other device hard_irq handler gpiod_x() raw_spin_lock_irqsave() -- oops
Actually no oops here. other drivers don't hold the same spinlock of this driver.
huh. driver/module A requests gpio and uses it in its hard_irq handler by calling GPIO API (Like gpiod_set_value()), those will go to this driver and end up in omap_gpio_set().
Yes, this could be a corner though it doesn't make any sense to use IRQF_NO_THREAD for this kind of driver/module A on rt as this will defeat the purpose of preemption by adding a long irqsoff section.
Since it cannot completely avoid this lockdep issue, I think that it is pointless to continue struggling with this patch which is changing an irq dispatcher driver any more.
But in general, what are the benefit of such changes at all, except better
marking
call context annotation, so we are spending so much time on it?
TBH, the benefit is really tiny except code cleanup. just curious how things
could
be different while it happens in an irq dispatcher's handler.
-- Best regards, Grygorii
Thanks Barry
On Fri, Feb 12, 2021 at 12:53 PM Grygorii Strashko grygorii.strashko@ti.com wrote:
The worst RT case I can imagine is when gpio API is still called from hard IRQ context by some other device driver - some toggling for example. Note. RT or "threadirqs" does not mean gpiochip become sleepable.
In this case: threaded handler raw_spin_lock IRQ from other device hard_irq handler gpiod_x() raw_spin_lock_irqsave() -- oops
Good point, I had missed the fact that drivers can call gpio functions from hardirq context when I replied earlier, gpio is clearly special here.
Arnd
-----Original Message----- From: Arnd Bergmann [mailto:arnd@kernel.org] Sent: Saturday, February 13, 2021 9:23 AM To: Grygorii Strashko grygorii.strashko@ti.com Cc: Song Bao Hua (Barry Song) song.bao.hua@hisilicon.com; Andy Shevchenko andy.shevchenko@gmail.com; luojiaxing luojiaxing@huawei.com; Linus Walleij linus.walleij@linaro.org; Santosh Shilimkar ssantosh@kernel.org; Kevin Hilman khilman@kernel.org; open list:GPIO SUBSYSTEM linux-gpio@vger.kernel.org; linux-kernel@vger.kernel.org; linuxarm@openeuler.org Subject: Re: [Linuxarm] Re: [PATCH for next v1 1/2] gpio: omap: Replace raw_spin_lock_irqsave with raw_spin_lock in omap_gpio_irq_handler()
On Fri, Feb 12, 2021 at 12:53 PM Grygorii Strashko grygorii.strashko@ti.com wrote:
The worst RT case I can imagine is when gpio API is still called from hard
IRQ context by some
other device driver - some toggling for example. Note. RT or "threadirqs" does not mean gpiochip become sleepable.
In this case: threaded handler raw_spin_lock IRQ from other device hard_irq handler gpiod_x() raw_spin_lock_irqsave() -- oops
Good point, I had missed the fact that drivers can call gpio functions from hardirq context when I replied earlier, gpio is clearly special here.
Yes. Gpio provides APIs, thus, other drivers can go directly into the territory of gpio driver.
Another one which is even more special might be m68k, which I cc-ed you yesterday: https://lore.kernel.org/lkml/c46ddb954cfe45d9849c911271d7ec23@hisilicon.com/
Arnd
Thanks Barry
On Fri, Feb 12, 2021 at 11:42 AM Song Bao Hua (Barry Song) song.bao.hua@hisilicon.com wrote:
Ok, second thought. irqsave before generic_handle_irq() won't defeat the purpose of preemption too much as the dispatched irq handlers by gpiochip will run in their own threads but not in the thread of gpiochip's handler.
so looks like this patch can improve by:
- move other raw_spin_lock_irqsave to raw_spin_lock;
- keep the raw_spin_lock_irqsave before generic_handle_irq() to mute
the warning in genirq.
It seems that the other drivers just call handle_nested_irq() instead of generic_handle_irq().
Arnd
On Fri, Feb 12, 2021 at 11:59:28AM +0100, Arnd Bergmann wrote:
On Fri, Feb 12, 2021 at 11:42 AM Song Bao Hua (Barry Song) song.bao.hua@hisilicon.com wrote:
Ok, second thought. irqsave before generic_handle_irq() won't defeat the purpose of preemption too much as the dispatched irq handlers by gpiochip will run in their own threads but not in the thread of gpiochip's handler.
so looks like this patch can improve by:
- move other raw_spin_lock_irqsave to raw_spin_lock;
- keep the raw_spin_lock_irqsave before generic_handle_irq() to mute
the warning in genirq.
It seems that the other drivers just call handle_nested_irq() instead of generic_handle_irq().
And IIRC all of them request threaded IRQ explicitly.
Sorry, my operation error causes a patch missing from this patch set. I re-send the patch set. Please check the new one.
On 2021/2/8 16:56, Luo Jiaxing wrote:
There is no need to use API with _irqsave in hard IRQ handler, So replace those with spin_lock.
Luo Jiaxing (2): gpio: omap: Replace raw_spin_lock_irqsave with raw_spin_lock in omap_gpio_irq_handler() gpio: grgpio: Replace spin_lock_irqsave with spin_lock in grgpio_irq_handler()
drivers/gpio/gpio-grgpio.c | 5 ++--- drivers/gpio/gpio-omap.c | 15 ++++++--------- 2 files changed, 8 insertions(+), 12 deletions(-)
On Mon, Feb 8, 2021 at 11:11 AM luojiaxing luojiaxing@huawei.com wrote:
Sorry, my operation error causes a patch missing from this patch set. I re-send the patch set. Please check the new one.
What is the new one?! You have to give proper versioning and change log for your series.
On 2021/2/8 16:56, Luo Jiaxing wrote:
There is no need to use API with _irqsave in hard IRQ handler, So replace those with spin_lock.
How do you know that another CPU in the system can't serve the following interrupt from the hardware at the same time?
On 2021/2/8 21:28, Andy Shevchenko wrote:
On Mon, Feb 8, 2021 at 11:11 AM luojiaxing luojiaxing@huawei.com wrote:
Sorry, my operation error causes a patch missing from this patch set. I re-send the patch set. Please check the new one.
What is the new one?! You have to give proper versioning and change log for your series.
sure, I will send a new one later, but let me answer your question first.
On 2021/2/8 16:56, Luo Jiaxing wrote:
There is no need to use API with _irqsave in hard IRQ handler, So replace those with spin_lock.
How do you know that another CPU in the system can't serve the following interrupt from the hardware at the same time?
Yes, I have some question before.
There are some similar discussion here, please take a look, Song baohua explained it more professionally.
https://lore.kernel.org/lkml/e949a474a9284ac6951813bfc8b34945@hisilicon.com/
Here are some excerpts from the discussion:
I think the code disabling irq in hardIRQ is simply wrong. Since this commit https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... genirq: Run irq handlers with interrupts disabled
interrupt handlers are definitely running in a irq-disabled context unless irq handlers enable them explicitly in the handler to permit other interrupts.
Thanks
Jiaxing
On Tue, Feb 9, 2021 at 11:24 AM luojiaxing luojiaxing@huawei.com wrote:
On 2021/2/8 21:28, Andy Shevchenko wrote:
On Mon, Feb 8, 2021 at 11:11 AM luojiaxing luojiaxing@huawei.com wrote:
Sorry, my operation error causes a patch missing from this patch set. I re-send the patch set. Please check the new one.
What is the new one?! You have to give proper versioning and change log for your series.
sure, I will send a new one later, but let me answer your question first.
On 2021/2/8 16:56, Luo Jiaxing wrote:
There is no need to use API with _irqsave in hard IRQ handler, So replace those with spin_lock.
How do you know that another CPU in the system can't serve the
The keyword here is: *another*.
following interrupt from the hardware at the same time?
Yes, I have some question before.
There are some similar discussion here, please take a look, Song baohua explained it more professionally.
https://lore.kernel.org/lkml/e949a474a9284ac6951813bfc8b34945@hisilicon.com/
Here are some excerpts from the discussion:
I think the code disabling irq in hardIRQ is simply wrong.
Why?
Since this commit https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... genirq: Run irq handlers with interrupts disabled
interrupt handlers are definitely running in a irq-disabled context unless irq handlers enable them explicitly in the handler to permit other interrupts.
This doesn't explain any changes in the behaviour on SMP. IRQ line can be disabled on a few stages: a) on the source (IP that generates an event) b) on IRQ router / controller c) on CPU side
The commit above is discussing (rightfully!) the problem when all interrupts are being served by a *single* core. Nobody prevents them from being served by *different* cores simultaneously. Also, see [1].
[1]: https://www.kernel.org/doc/htmldocs/kernel-locking/cheatsheet.html
On 2021/2/9 17:42, Andy Shevchenko wrote:
On Tue, Feb 9, 2021 at 11:24 AM luojiaxing luojiaxing@huawei.com wrote:
On 2021/2/8 21:28, Andy Shevchenko wrote:
On Mon, Feb 8, 2021 at 11:11 AM luojiaxing luojiaxing@huawei.com wrote:
Sorry, my operation error causes a patch missing from this patch set. I re-send the patch set. Please check the new one.
What is the new one?! You have to give proper versioning and change log for your series.
sure, I will send a new one later, but let me answer your question first.
On 2021/2/8 16:56, Luo Jiaxing wrote:
There is no need to use API with _irqsave in hard IRQ handler, So replace those with spin_lock.
How do you know that another CPU in the system can't serve the
The keyword here is: *another*.
ooh, sorry, now I got your point.
As to me, I don't think another CPU can serve the IRQ when one CPU runing hard IRQ handler,
except it's a per CPU interrupts.
The following is a simple call logic when IRQ come.
elx_irq -> handle_arch_irq -> __handle_domain_irq -> desc->handle_irq -> handle_irq_event
Assume that two CPUs receive the same IRQ and enter the preceding process. Both of them will go to desc->handle_irq().
In handle_irq(), raw_spin_lock(&desc->lock) always be called first. Therefore, even if two CPUs are running handle_irq(),
only one can get the spin lock. Assume that CPU A obtains the spin lock. Then CPU A will sets the status of irq_data to
IRQD_IRQ_INPROGRESS in handle_irq_event() and releases the spin lock. Even though CPU B gets the spin lock later and
continue to run handle_irq(), but the check of irq_may_run(desc) causes it to exit.
so, I think we don't own the situation that two CPU server the hard IRQ handler at the same time.
following interrupt from the hardware at the same time?
Yes, I have some question before.
There are some similar discussion here, please take a look, Song baohua explained it more professionally.
https://lore.kernel.org/lkml/e949a474a9284ac6951813bfc8b34945@hisilicon.com/
Here are some excerpts from the discussion:
I think the code disabling irq in hardIRQ is simply wrong.
Why?
I mention the following call before.
elx_irq -> handle_arch_irq -> __handle_domain_irq -> desc->handle_irq -> handle_irq_event
__handle_domain_irq() will call irq_enter(), it ensures that the IRQ processing of the current CPU can not be preempted.
So I think this is the reason why Song baohua said it's not need to disable IRQ in hardIRQ handler.
Since this commit https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... genirq: Run irq handlers with interrupts disabled
interrupt handlers are definitely running in a irq-disabled context unless irq handlers enable them explicitly in the handler to permit other interrupts.
This doesn't explain any changes in the behaviour on SMP. IRQ line can be disabled on a few stages: a) on the source (IP that generates an event) b) on IRQ router / controller c) on CPU side
yes, you are right.
The commit above is discussing (rightfully!) the problem when all interrupts are being served by a *single* core. Nobody prevents them from being served by *different* cores simultaneously. Also, see [1].
I check [1], quite useful description about locking, thanks. But you can
see Table of locking Requirements
Between IRQ handler A and IRQ handle A, it's no need for a SLIS.
Thanks
Jiaxing
On Wed, Feb 10, 2021 at 5:43 AM luojiaxing luojiaxing@huawei.com wrote:
On 2021/2/9 17:42, Andy Shevchenko wrote:
On Tue, Feb 9, 2021 at 11:24 AM luojiaxing luojiaxing@huawei.com wrote:
On 2021/2/8 21:28, Andy Shevchenko wrote:
On Mon, Feb 8, 2021 at 11:11 AM luojiaxing luojiaxing@huawei.com wrote:
On 2021/2/8 16:56, Luo Jiaxing wrote:
There is no need to use API with _irqsave in hard IRQ handler, So replace those with spin_lock.
How do you know that another CPU in the system can't serve the
The keyword here is: *another*.
ooh, sorry, now I got your point.
As to me, I don't think another CPU can serve the IRQ when one CPU runing hard IRQ handler,
Why is it so? Each CPU can serve IRQs separately.
except it's a per CPU interrupts.
I didn't get how it is related.
The following is a simple call logic when IRQ come.
elx_irq -> handle_arch_irq -> __handle_domain_irq -> desc->handle_irq -> handle_irq_event
What is `elx_irq()`? I haven't found any mention of this in the kernel source tree. But okay, it shouldn't prevent our discussion.
Assume that two CPUs receive the same IRQ and enter the preceding process. Both of them will go to desc->handle_irq().
Ah, I'm talking about the same IRQ by number (like Linux IRQ number, means from the same source), but with different sequence number (means two consequent events).
In handle_irq(), raw_spin_lock(&desc->lock) always be called first. Therefore, even if two CPUs are running handle_irq(),
only one can get the spin lock. Assume that CPU A obtains the spin lock. Then CPU A will sets the status of irq_data to
IRQD_IRQ_INPROGRESS in handle_irq_event() and releases the spin lock. Even though CPU B gets the spin lock later and
continue to run handle_irq(), but the check of irq_may_run(desc) causes it to exit.
so, I think we don't own the situation that two CPU server the hard IRQ handler at the same time.
Okay. Assuming your analysis is correct, have you considered the case when all IRQ handlers are threaded? (There is a kernel command line option to force this)
following interrupt from the hardware at the same time?
Yes, I have some question before.
There are some similar discussion here, please take a look, Song baohua explained it more professionally.
https://lore.kernel.org/lkml/e949a474a9284ac6951813bfc8b34945@hisilicon.com/
Here are some excerpts from the discussion:
I think the code disabling irq in hardIRQ is simply wrong.
Why?
I mention the following call before.
elx_irq -> handle_arch_irq -> __handle_domain_irq -> desc->handle_irq -> handle_irq_event
__handle_domain_irq() will call irq_enter(), it ensures that the IRQ processing of the current CPU can not be preempted.
So I think this is the reason why Song baohua said it's not need to disable IRQ in hardIRQ handler.
Since this commit https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... genirq: Run irq handlers with interrupts disabled
interrupt handlers are definitely running in a irq-disabled context unless irq handlers enable them explicitly in the handler to permit other interrupts.
This doesn't explain any changes in the behaviour on SMP. IRQ line can be disabled on a few stages: a) on the source (IP that generates an event) b) on IRQ router / controller c) on CPU side
yes, you are right.
The commit above is discussing (rightfully!) the problem when all interrupts are being served by a *single* core. Nobody prevents them from being served by *different* cores simultaneously. Also, see [1].
I check [1], quite useful description about locking, thanks. But you can see Table of locking Requirements
Between IRQ handler A and IRQ handle A, it's no need for a SLIS.
Right, but it's not the case in the patches you provided.
-- With Best Regards, Andy Shevchenko
-----Original Message----- From: Andy Shevchenko [mailto:andy.shevchenko@gmail.com] Sent: Wednesday, February 10, 2021 11:51 PM To: luojiaxing luojiaxing@huawei.com Cc: Linus Walleij linus.walleij@linaro.org; Andy Shevchenko andriy.shevchenko@linux.intel.com; Grygorii Strashko grygorii.strashko@ti.com; Santosh Shilimkar ssantosh@kernel.org; Kevin Hilman khilman@kernel.org; open list:GPIO SUBSYSTEM linux-gpio@vger.kernel.org; Linux Kernel Mailing List linux-kernel@vger.kernel.org; linuxarm@openeuler.org Subject: [Linuxarm] Re: [PATCH for next v1 0/2] gpio: few clean up patches to replace spin_lock_irqsave with spin_lock
On Wed, Feb 10, 2021 at 5:43 AM luojiaxing luojiaxing@huawei.com wrote:
On 2021/2/9 17:42, Andy Shevchenko wrote:
On Tue, Feb 9, 2021 at 11:24 AM luojiaxing luojiaxing@huawei.com wrote:
On 2021/2/8 21:28, Andy Shevchenko wrote:
On Mon, Feb 8, 2021 at 11:11 AM luojiaxing luojiaxing@huawei.com wrote:
On 2021/2/8 16:56, Luo Jiaxing wrote: > There is no need to use API with _irqsave in hard IRQ handler, So replace > those with spin_lock.
How do you know that another CPU in the system can't serve the
The keyword here is: *another*.
ooh, sorry, now I got your point.
As to me, I don't think another CPU can serve the IRQ when one CPU runing hard IRQ handler,
Why is it so? Each CPU can serve IRQs separately.
except it's a per CPU interrupts.
I didn't get how it is related.
The following is a simple call logic when IRQ come.
elx_irq -> handle_arch_irq -> __handle_domain_irq -> desc->handle_irq -> handle_irq_event
What is `elx_irq()`? I haven't found any mention of this in the kernel source tree. But okay, it shouldn't prevent our discussion.
Assume that two CPUs receive the same IRQ and enter the preceding process. Both of them will go to desc->handle_irq().
Ah, I'm talking about the same IRQ by number (like Linux IRQ number, means from the same source), but with different sequence number (means two consequent events).
In handle_irq(), raw_spin_lock(&desc->lock) always be called first. Therefore, even if two CPUs are running handle_irq(),
only one can get the spin lock. Assume that CPU A obtains the spin lock. Then CPU A will sets the status of irq_data to
IRQD_IRQ_INPROGRESS in handle_irq_event() and releases the spin lock. Even though CPU B gets the spin lock later and
continue to run handle_irq(), but the check of irq_may_run(desc) causes it to exit.
so, I think we don't own the situation that two CPU server the hard IRQ handler at the same time.
Okay. Assuming your analysis is correct, have you considered the case when all IRQ handlers are threaded? (There is a kernel command line option to force this)
following interrupt from the hardware at the same time?
Yes, I have some question before.
There are some similar discussion here, please take a look, Song baohua explained it more professionally.
https://lore.kernel.org/lkml/e949a474a9284ac6951813bfc8b34945@hisilicon.co m/
Here are some excerpts from the discussion:
I think the code disabling irq in hardIRQ is simply wrong.
Why?
I mention the following call before.
elx_irq -> handle_arch_irq -> __handle_domain_irq -> desc->handle_irq -> handle_irq_event
__handle_domain_irq() will call irq_enter(), it ensures that the IRQ processing of the current CPU can not be preempted.
So I think this is the reason why Song baohua said it's not need to disable IRQ in hardIRQ handler.
Since this commit
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/ ?id=e58aa3d2d0cc
genirq: Run irq handlers with interrupts disabled
interrupt handlers are definitely running in a irq-disabled context unless irq handlers enable them explicitly in the handler to permit other interrupts.
This doesn't explain any changes in the behaviour on SMP. IRQ line can be disabled on a few stages: a) on the source (IP that generates an event) b) on IRQ router / controller c) on CPU side
yes, you are right.
The commit above is discussing (rightfully!) the problem when all interrupts are being served by a *single* core. Nobody prevents them from being served by *different* cores simultaneously. Also, see [1].
I check [1], quite useful description about locking, thanks. But you can see Table of locking Requirements
Between IRQ handler A and IRQ handle A, it's no need for a SLIS.
Right, but it's not the case in the patches you provided.
The code still holds spin_lock. So if two cpus call same IRQ handler, spin_lock makes them spin; and if interrupts are threaded, spin_lock makes two threads run the same handler one by one.
-- With Best Regards, Andy Shevchenko
Thanks Barry
On Wed, Feb 10, 2021 at 11:50:45AM +0000, Song Bao Hua (Barry Song) wrote:
-----Original Message----- From: Andy Shevchenko [mailto:andy.shevchenko@gmail.com] Sent: Wednesday, February 10, 2021 11:51 PM On Wed, Feb 10, 2021 at 5:43 AM luojiaxing luojiaxing@huawei.com wrote:
On 2021/2/9 17:42, Andy Shevchenko wrote:
...
Between IRQ handler A and IRQ handle A, it's no need for a SLIS.
Right, but it's not the case in the patches you provided.
The code still holds spin_lock. So if two cpus call same IRQ handler, spin_lock makes them spin; and if interrupts are threaded, spin_lock makes two threads run the same handler one by one.
If you run on an SMP system and it happens that spin_lock_irqsave() just immediately after spin_unlock(), you will get into the troubles. Am I mistaken?
I think this entire activity is a carefully crafted mine field for the future syzcaller and fuzzers alike. I don't believe there are no side effects in a long term on all possible systems and configurations (including forced threaded IRQ handlers).
I would love to see a better explanation in the commit message of such patches which makes it clear that there are *no* side effects.
For time being, NAK to the all patches of this kind.
-----Original Message----- From: Andy Shevchenko [mailto:andy.shevchenko@gmail.com] Sent: Thursday, February 11, 2021 3:57 AM To: Song Bao Hua (Barry Song) song.bao.hua@hisilicon.com Cc: luojiaxing luojiaxing@huawei.com; Linus Walleij linus.walleij@linaro.org; Grygorii Strashko grygorii.strashko@ti.com; Santosh Shilimkar ssantosh@kernel.org; Kevin Hilman khilman@kernel.org; open list:GPIO SUBSYSTEM linux-gpio@vger.kernel.org; Linux Kernel Mailing List linux-kernel@vger.kernel.org; linuxarm@openeuler.org Subject: Re: [Linuxarm] Re: [PATCH for next v1 0/2] gpio: few clean up patches to replace spin_lock_irqsave with spin_lock
On Wed, Feb 10, 2021 at 11:50:45AM +0000, Song Bao Hua (Barry Song) wrote:
-----Original Message----- From: Andy Shevchenko [mailto:andy.shevchenko@gmail.com] Sent: Wednesday, February 10, 2021 11:51 PM On Wed, Feb 10, 2021 at 5:43 AM luojiaxing luojiaxing@huawei.com wrote:
On 2021/2/9 17:42, Andy Shevchenko wrote:
...
Between IRQ handler A and IRQ handle A, it's no need for a SLIS.
Right, but it's not the case in the patches you provided.
The code still holds spin_lock. So if two cpus call same IRQ handler, spin_lock makes them spin; and if interrupts are threaded, spin_lock makes two threads run the same handler one by one.
If you run on an SMP system and it happens that spin_lock_irqsave() just immediately after spin_unlock(), you will get into the troubles. Am I mistaken?
Hi Andy, Thanks for your reply.
But I don't agree spin_lock_irqsave() just immediately after spin_unlock() could a problem on SMP. When the 1st cpu releases spinlock by spin_unlock, it has completed its section of accessing the critical data, then 2nd cpu gets the spin_lock. These two CPUs won't have overlap on accessing the same data.
I think this entire activity is a carefully crafted mine field for the future syzcaller and fuzzers alike. I don't believe there are no side effects in a long term on all possible systems and configurations (including forced threaded IRQ handlers).
Also I don't understand why forced threaded IRQ could be a problem. Since IRQ has been a thread, this actually makes the situation much simpler than non-threaded IRQ. Since all threads including those IRQ threads want to hold spin_lock, they won't access the same critical data at the same time either.
I would love to see a better explanation in the commit message of such patches which makes it clear that there are *no* side effects.
People had the same questions before, But I guess the discussion in this commit has led to a better commit log:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...
For time being, NAK to the all patches of this kind.
Fair enough, if you expect better explanation, I agree the commit log is too short.
-- With Best Regards, Andy Shevchenko
Thanks Barry
On Wed, Feb 10, 2021 at 10:42 PM Song Bao Hua (Barry Song) song.bao.hua@hisilicon.com wrote:
-----Original Message----- From: Andy Shevchenko [mailto:andy.shevchenko@gmail.com] Sent: Thursday, February 11, 2021 3:57 AM On Wed, Feb 10, 2021 at 11:50:45AM +0000, Song Bao Hua (Barry Song) wrote:
-----Original Message----- From: Andy Shevchenko [mailto:andy.shevchenko@gmail.com] Sent: Wednesday, February 10, 2021 11:51 PM On Wed, Feb 10, 2021 at 5:43 AM luojiaxing luojiaxing@huawei.com wrote:
On 2021/2/9 17:42, Andy Shevchenko wrote:
...
Between IRQ handler A and IRQ handle A, it's no need for a SLIS.
Right, but it's not the case in the patches you provided.
The code still holds spin_lock. So if two cpus call same IRQ handler, spin_lock makes them spin; and if interrupts are threaded, spin_lock makes two threads run the same handler one by one.
If you run on an SMP system and it happens that spin_lock_irqsave() just immediately after spin_unlock(), you will get into the troubles. Am I mistaken?
Hi Andy, Thanks for your reply.
But I don't agree spin_lock_irqsave() just immediately after spin_unlock() could a problem on SMP. When the 1st cpu releases spinlock by spin_unlock, it has completed its section of accessing the critical data, then 2nd cpu gets the spin_lock. These two CPUs won't have overlap on accessing the same data.
I think this entire activity is a carefully crafted mine field for the future syzcaller and fuzzers alike. I don't believe there are no side effects in a long term on all possible systems and configurations (including forced threaded IRQ handlers).
Also I don't understand why forced threaded IRQ could be a problem. Since IRQ has been a thread, this actually makes the situation much simpler than non-threaded IRQ. Since all threads including those IRQ threads want to hold spin_lock, they won't access the same critical data at the same time either.
I would love to see a better explanation in the commit message of such patches which makes it clear that there are *no* side effects.
People had the same questions before, But I guess the discussion in this commit has led to a better commit log:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...
For time being, NAK to the all patches of this kind.
Fair enough, if you expect better explanation, I agree the commit log is too short.
Yes, my main concern that the commit message style as "I feel it's wrong" is inappropriate to this kind of patch. The one you pointed out above is better, you may give it even more thrust by explaining why it was in the first place and what happened between the driver gained this type of spinlock and your patch.
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Andy Shevchenko -
Arnd Bergmann -
Grygorii Strashko -
Luo Jiaxing -
luojiaxing
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Song Bao Hua (Barry Song)