Linux 5.10.215

[thirdparty/kernel/stable-queue.git] / releases / 5.10.215 / ring-buffer-do-not-set-shortest_full-when-full-targe.patch

From 97a7f84a7a2f0086ff610254ed3c24b62a8627b5 Mon Sep 17 00:00:00 2001
From: Sasha Levin <sashal@kernel.org>
Date: Tue, 12 Mar 2024 11:56:41 -0400
Subject: ring-buffer: Do not set shortest_full when full target is hit

From: Steven Rostedt (Google) <rostedt@goodmis.org>

[ Upstream commit 761d9473e27f0c8782895013a3e7b52a37c8bcfc ]

The rb_watermark_hit() checks if the amount of data in the ring buffer is
above the percentage level passed in by the "full" variable. If it is, it
returns true.

But it also sets the "shortest_full" field of the cpu_buffer that informs
writers that it needs to call the irq_work if the amount of data on the
ring buffer is above the requested amount.

The rb_watermark_hit() always sets the shortest_full even if the amount in
the ring buffer is what it wants. As it is not going to wait, because it
has what it wants, there's no reason to set shortest_full.

Link: https://lore.kernel.org/linux-trace-kernel/20240312115641.6aa8ba08@gandalf.local.home

Cc: stable@vger.kernel.org
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Fixes: 42fb0a1e84ff5 ("tracing/ring-buffer: Have polling block on watermark")
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 kernel/trace/ring_buffer.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 936b560989a3e..5b665e5991bf7 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -887,9 +887,10 @@ static bool rb_watermark_hit(struct trace_buffer *buffer, int cpu, int full)
 		pagebusy = cpu_buffer->reader_page == cpu_buffer->commit_page;
 		ret = !pagebusy && full_hit(buffer, cpu, full);
 
-		if (!cpu_buffer->shortest_full ||
-		    cpu_buffer->shortest_full > full)
-			cpu_buffer->shortest_full = full;
+		if (!ret && (!cpu_buffer->shortest_full ||
+			     cpu_buffer->shortest_full > full)) {
+		    cpu_buffer->shortest_full = full;
+		}
 		raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
 	}
 	return ret;
-- 
2.43.0