From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: stable@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	patches@lists.linux.dev,
	Vincent Donnefort <vdonnefort@google.com>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	Steven Rostedt <rostedt@goodmis.org>
Subject: [PATCH 6.12 0839/1102] ring-buffer: Acquire the lock with irqsave in rb_wake_up_waiters()
Date: Thu, 17 Sep 2026 16:13:02 +0100
Message-ID: <20260917151601.583564261@linuxfoundation.org>
In-Reply-To: <20260917151539.408551884@linuxfoundation.org>
References: <20260917151539.408551884@linuxfoundation.org>
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6.12-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

commit 815e07c8fe885a87751c2496a30ae0dcd4118210 upstream.

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 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.

Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260911102152.YEtwkBj9@linutronix.de
Fixes: 68282dd930ea3 ("ring-buffer: Fix resetting of shortest_full")
Reviewed-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 kernel/trace/ring_buffer.c |   13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -837,14 +837,13 @@ static void rb_wake_up_waiters(struct ir
 		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);
 	}