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

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

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