[PATCH] ring-buffer: Acquire the lock with irqsave in rb_wake_up_waiters()

[PATCH] ring-buffer: Acquire the lock with irqsave in rb_wake_up_waiters()

[Sebastian Andrzej Siewior]

rb_wake_up_waiters() is a irq_work callback which is initialized with
init_irq_work(). As such it will be invoked in thread context on
PREEMPT_RT. Invoking the callback in IRQ context on PREEMPT_RT is not an
option due its usage of wake_up_all().
Since this callback may run in thread context, it needs to acqurie
ring_buffer_per_cpu::reader_lock with disabling interrupts and may not
assume that they are disabled.

Use raw_spinlock_irqsave() to acquire ring_buffer_per_cpu::reader_lock.

Fixes: 68282dd930ea3 ("ring-buffer: Fix resetting of shortest_full")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 kernel/trace/ring_buffer.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 9c03a555a6ba2..681f9daf6fabb 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -904,14 +904,13 @@ static void rb_wake_up_waiters(struct irq_work *work)
 		struct ring_buffer_per_cpu *cpu_buffer =
 			container_of(rbwork, struct ring_buffer_per_cpu, irq_work);
 
-		/* Called from interrupt context */
-		raw_spin_lock(&cpu_buffer->reader_lock);
-		rbwork->wakeup_full = false;
-		rbwork->full_waiters_pending = false;
+		scoped_guard(raw_spinlock_irqsave, &cpu_buffer->reader_lock) {
+			rbwork->wakeup_full = false;
+			rbwork->full_waiters_pending = false;
 
-		/* Waking up all waiters, they will reset the shortest full */
-		cpu_buffer->shortest_full = 0;
-		raw_spin_unlock(&cpu_buffer->reader_lock);
+			/* Waking up all waiters, they will reset the shortest full */
+			cpu_buffer->shortest_full = 0;
+		}
 
 		wake_up_all(&rbwork->full_waiters);
 	}
-- 
2.55.0

Re: [PATCH] ring-buffer: Acquire the lock with irqsave in rb_wake_up_waiters()

[Vincent Donnefort]

On Fri, Sep 11, 2026 at 12:21:52PM +0200, Sebastian Andrzej Siewior wrote:
> rb_wake_up_waiters() is a irq_work callback which is initialized with
> init_irq_work(). As such it will be invoked in thread context on
> PREEMPT_RT. Invoking the callback in IRQ context on PREEMPT_RT is not an
> option due its usage of wake_up_all().
> Since this callback may run in thread context, it needs to acqurie

nit: typo "acquire" 

> ring_buffer_per_cpu::reader_lock with disabling interrupts and may not
> assume that they are disabled.
> 
> Use raw_spinlock_irqsave() to acquire ring_buffer_per_cpu::reader_lock.
> 
> Fixes: 68282dd930ea3 ("ring-buffer: Fix resetting of shortest_full")
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> ---
>  kernel/trace/ring_buffer.c | 13 ++++++-------
>  1 file changed, 6 insertions(+), 7 deletions(-)
> 
> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> index 9c03a555a6ba2..681f9daf6fabb 100644
> --- a/kernel/trace/ring_buffer.c
> +++ b/kernel/trace/ring_buffer.c
> @@ -904,14 +904,13 @@ static void rb_wake_up_waiters(struct irq_work *work)
>  		struct ring_buffer_per_cpu *cpu_buffer =
>  			container_of(rbwork, struct ring_buffer_per_cpu, irq_work);
>  
> -		/* Called from interrupt context */
> -		raw_spin_lock(&cpu_buffer->reader_lock);
> -		rbwork->wakeup_full = false;
> -		rbwork->full_waiters_pending = false;
> +		scoped_guard(raw_spinlock_irqsave, &cpu_buffer->reader_lock) {
> +			rbwork->wakeup_full = false;
> +			rbwork->full_waiters_pending = false;
>  
> -		/* Waking up all waiters, they will reset the shortest full */
> -		cpu_buffer->shortest_full = 0;
> -		raw_spin_unlock(&cpu_buffer->reader_lock);
> +			/* Waking up all waiters, they will reset the shortest full */
> +			cpu_buffer->shortest_full = 0;
> +		}
>  
>  		wake_up_all(&rbwork->full_waiters);
>  	}
> -- 
> 2.55.0
> 
> 

Reviewed-by: Vincent Donnefort <vdonnefort@google.com>