[PATCH 5.15.y] ring-buffer: Acquire the lock with irqsave in rb_wake_up_waiters()

[Sasha Levin <sashal@kernel.org>]

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

[ Upstream commit 815e07c8fe885a87751c2496a30ae0dcd4118210 ]

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>
[ Replaced scoped_guard() with explicit raw_spin_lock_irqsave()/raw_spin_unlock_irqrestore() calls for GNU89 compatibility. ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 kernel/trace/ring_buffer.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 84f3b0d0bc887..9c43f01fa2c2a 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -877,15 +877,15 @@ static void rb_wake_up_waiters(struct irq_work *work)
 		/* Only cpu_buffer sets the above flags */
 		struct ring_buffer_per_cpu *cpu_buffer =
 			container_of(rbwork, struct ring_buffer_per_cpu, irq_work);
+		unsigned long flags;
 
-		/* Called from interrupt context */
-		raw_spin_lock(&cpu_buffer->reader_lock);
+		raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
 		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);
+		raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
 
 		wake_up_all(&rbwork->full_waiters);
 	}
-- 
2.53.0