[PATCH] clocksource/i8253: Acquire the lock disabled interrupts.

[PATCH] clocksource/i8253: Acquire the lock disabled interrupts.

[Sebastian Andrzej Siewior]

On x86 during boot, clockevent_i8253_disable() can be invoked via
x86_late_time_init -> hpet_time_init() -> pit_timer_init() which happens
with enabled interrupts.
If some of the old i8253 hardware is actually used then lockdep will
notice that i8253_lock is used in hardirq context. This causes lockdep
to complain because it observed the lock being acquired with enabled
interrupts and in hardirq context.

Make clockevent_i8253_disable() acquire the lock with disabled
interrupts.

Fixes: c8c4076723dac ("x86/timer: Skip PIT initialization on modern chipsets")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 drivers/clocksource/i8253.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/clocksource/i8253.c b/drivers/clocksource/i8253.c
index 39f7c2d736d16..67dcd9c8f1875 100644
--- a/drivers/clocksource/i8253.c
+++ b/drivers/clocksource/i8253.c
@@ -103,8 +103,9 @@ int __init clocksource_i8253_init(void)
 #ifdef CONFIG_CLKEVT_I8253
 void clockevent_i8253_disable(void)
 {
-	raw_spin_lock(&i8253_lock);
+	unsigned long flags;
 
+	raw_spin_lock_irqsave(&i8253_lock, flags);
 	/*
 	 * Writing the MODE register should stop the counter, according to
 	 * the datasheet. This appears to work on real hardware (well, on
@@ -133,7 +134,7 @@ void clockevent_i8253_disable(void)
 
 	outb_p(0x30, PIT_MODE);
 
-	raw_spin_unlock(&i8253_lock);
+	raw_spin_unlock_irqrestore(&i8253_lock, flags);
 }
 
 static int pit_shutdown(struct clock_event_device *evt)
-- 
2.49.0

Re: [PATCH] clocksource/i8253: Acquire the lock disabled interrupts.

[Sebastian Andrzej Siewior]

On 2025-04-04 15:31:17 [+0200], To linux-kernel@vger.kernel.org wrote:
> On x86 during boot, clockevent_i8253_disable() can be invoked via
> x86_late_time_init -> hpet_time_init() -> pit_timer_init() which happens
> with enabled interrupts.
> If some of the old i8253 hardware is actually used then lockdep will
> notice that i8253_lock is used in hardirq context. This causes lockdep
> to complain because it observed the lock being acquired with enabled
> interrupts and in hardirq context.
> 
> Make clockevent_i8253_disable() acquire the lock with disabled
> interrupts.
> 
> Fixes: c8c4076723dac ("x86/timer: Skip PIT initialization on modern chipsets")
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

A gentle reminder.

Sebastian

Re: [PATCH] clocksource/i8253: Acquire the lock disabled interrupts.

[Thomas Gleixner]

On Fri, Apr 04 2025 at 15:31, Sebastian Andrzej Siewior wrote:
> On x86 during boot, clockevent_i8253_disable() can be invoked via
> x86_late_time_init -> hpet_time_init() -> pit_timer_init() which happens
> with enabled interrupts.
> If some of the old i8253 hardware is actually used then lockdep will
> notice that i8253_lock is used in hardirq context. This causes lockdep
> to complain because it observed the lock being acquired with enabled
> interrupts and in hardirq context.
>
> Make clockevent_i8253_disable() acquire the lock with disabled
> interrupts.

This sentence does not make sense. I'll fix it up...

> Fixes: c8c4076723dac ("x86/timer: Skip PIT initialization on modern chipsets")
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> ---
>  drivers/clocksource/i8253.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/clocksource/i8253.c b/drivers/clocksource/i8253.c
> index 39f7c2d736d16..67dcd9c8f1875 100644
> --- a/drivers/clocksource/i8253.c
> +++ b/drivers/clocksource/i8253.c
> @@ -103,8 +103,9 @@ int __init clocksource_i8253_init(void)
>  #ifdef CONFIG_CLKEVT_I8253
>  void clockevent_i8253_disable(void)
>  {
> -	raw_spin_lock(&i8253_lock);
> +	unsigned long flags;
>  
> +	raw_spin_lock_irqsave(&i8253_lock, flags);
>  	/*
>  	 * Writing the MODE register should stop the counter, according to
>  	 * the datasheet. This appears to work on real hardware (well, on
> @@ -133,7 +134,7 @@ void clockevent_i8253_disable(void)
>  
>  	outb_p(0x30, PIT_MODE);
>  
> -	raw_spin_unlock(&i8253_lock);
> +	raw_spin_unlock_irqrestore(&i8253_lock, flags);
>  }
>  
>  static int pit_shutdown(struct clock_event_device *evt)

[tip: timers/urgent] clocksource/i8253: Use raw_spinlock_irqsave() in clockevent_i8253_disable()

[tip-bot2 for Sebastian Andrzej Siewior]

The following commit has been merged into the timers/urgent branch of tip:

Commit-ID:     94cff94634e506a4a44684bee1875d2dbf782722
Gitweb:        https://git.kernel.org/tip/94cff94634e506a4a44684bee1875d2dbf782722
Author:        Sebastian Andrzej Siewior <bigeasy@linutronix.de>
AuthorDate:    Fri, 04 Apr 2025 15:31:16 +02:00
Committer:     Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Mon, 05 May 2025 15:34:49 +02:00

clocksource/i8253: Use raw_spinlock_irqsave() in clockevent_i8253_disable()

On x86 during boot, clockevent_i8253_disable() can be invoked via
x86_late_time_init -> hpet_time_init() -> pit_timer_init() which happens
with enabled interrupts.

If some of the old i8253 hardware is actually used then lockdep will notice
that i8253_lock is used in hard interrupt context. This causes lockdep to
complain because it observed the lock being acquired with interrupts
enabled and in hard interrupt context.

Make clockevent_i8253_disable() acquire the lock with
raw_spinlock_irqsave() to cure this.

[ tglx: Massage change log and use guard() ]

Fixes: c8c4076723dac ("x86/timer: Skip PIT initialization on modern chipsets")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/all/20250404133116.p-XRWJXf@linutronix.de
---
 drivers/clocksource/i8253.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/clocksource/i8253.c b/drivers/clocksource/i8253.c
index 39f7c2d..b603c25 100644
--- a/drivers/clocksource/i8253.c
+++ b/drivers/clocksource/i8253.c
@@ -103,7 +103,7 @@ int __init clocksource_i8253_init(void)
 #ifdef CONFIG_CLKEVT_I8253
 void clockevent_i8253_disable(void)
 {
-	raw_spin_lock(&i8253_lock);
+	guard(raw_spinlock_irqsave)(&i8253_lock);
 
 	/*
 	 * Writing the MODE register should stop the counter, according to
@@ -132,8 +132,6 @@ void clockevent_i8253_disable(void)
 	outb_p(0, PIT_CH0);
 
 	outb_p(0x30, PIT_MODE);
-
-	raw_spin_unlock(&i8253_lock);
 }
 
 static int pit_shutdown(struct clock_event_device *evt)