FAILED: patch "[PATCH] ring-buffer: Acquire the lock with irqsave in" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 815e07c8fe885a87751c2496a30ae0dcd4118210
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026091640-capacity-finalize-8fbc@gregkh' --subject-prefix 'PATCH 5.15.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 815e07c8fe885a87751c2496a30ae0dcd4118210 Mon Sep 17 00:00:00 2001
From: Sebastian Andrzej Siewior <[email protected]>
Date: Fri, 11 Sep 2026 12:21:52 +0200
Subject: [PATCH] ring-buffer: Acquire the lock with irqsave in
rb_wake_up_waiters()

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.

index 0e30c7bd6045..9bc8ce8c5676 100644
@@ -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);
 	}

From: Sebastian Andrzej Siewior <[email protected]>

[ 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.

---
 kernel/trace/ring_buffer.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

index 84f3b0d0bc887..9c43f01fa2c2a 100644
@@ -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