linux-kernel - [PATCH 1/8] ring-buffer: Allow mapped field to be set without mapping

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Message-ID: <20240306020005.461538701@goodmis.org>
Date: Tue, 05 Mar 2024 20:59:11 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org
Cc: Masami Hiramatsu <mhiramat@...nel.org>,
 Mark Rutland <mark.rutland@....com>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Vincent Donnefort <vdonnefort@...gle.com>,
 Joel Fernandes <joel@...lfernandes.org>,
 Daniel Bristot de Oliveira <bristot@...hat.com>,
 Ingo Molnar <mingo@...nel.org>,
 Peter Zijlstra <peterz@...radead.org>,
 suleiman@...gle.com,
 Thomas Gleixner <tglx@...utronix.de>,
 Vineeth Pillai <vineeth@...byteword.org>,
 Youssef Esmat <youssefesmat@...gle.com>,
 Beau Belgrave <beaub@...ux.microsoft.com>,
 Alexander Graf <graf@...zon.com>,
 Baoquan He <bhe@...hat.com>,
 Borislav Petkov <bp@...en8.de>,
 "Paul E. McKenney" <paulmck@...nel.org>,
 David Howells <dhowells@...hat.com>
Subject: [PATCH 1/8] ring-buffer: Allow mapped field to be set without mapping

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

In preparation for having the ring buffer mapped to a dedicated location,
which will have the same restrictions as user space memory mapped buffers,
allow it to use the "mapped" field of the ring_buffer_per_cpu structure
without having the user space meta page mapping.

When this starts using the mapped field, it will need to handle adding a
user space mapping (and removing it) from a ring buffer that is using a
dedicated memory range.

Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
---
 kernel/trace/ring_buffer.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 1d7d7a701867..524b2c185c88 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -5171,6 +5171,9 @@ static void rb_update_meta_page(struct ring_buffer_per_cpu *cpu_buffer)
 {
 	struct trace_buffer_meta *meta = cpu_buffer->meta_page;

+	if (!meta)
+		return;
+
 	meta->reader.read = cpu_buffer->reader_page->read;
 	meta->reader.id = cpu_buffer->reader_page->id;
 	meta->reader.lost_events = cpu_buffer->lost_events;
@@ -6159,7 +6162,7 @@ rb_get_mapped_buffer(struct trace_buffer *buffer, int cpu)

 	mutex_lock(&cpu_buffer->mapping_lock);

-	if (!cpu_buffer->mapped) {
+	if (!cpu_buffer->mapped || !cpu_buffer->meta_page) {
 		mutex_unlock(&cpu_buffer->mapping_lock);
 		return ERR_PTR(-ENODEV);
 	}
@@ -6217,7 +6220,7 @@ int ring_buffer_map(struct trace_buffer *buffer, int cpu)

 	mutex_lock(&cpu_buffer->mapping_lock);

-	if (cpu_buffer->mapped) {
+	if (cpu_buffer->meta_page) {
 		err = __rb_inc_dec_mapped(buffer, cpu_buffer, true);
 		mutex_unlock(&cpu_buffer->mapping_lock);
 		return err;
@@ -6247,7 +6250,7 @@ int ring_buffer_map(struct trace_buffer *buffer, int cpu)
 	raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);

 	rb_setup_ids_meta_page(cpu_buffer, subbuf_ids);
-	cpu_buffer->mapped = 1;
+	cpu_buffer->mapped++;

 	raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
 unlock:
-- 
2.43.0