linux-kernel - [PATCH] tracing: Update snapshot buffer on resize if it is allocated

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Date:   Sun, 10 Dec 2023 22:54:47 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     LKML <linux-kernel@...r.kernel.org>,
        Linux trace kernel <linux-trace-kernel@...r.kernel.org>
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: [PATCH] tracing: Update snapshot buffer on resize if it is
 allocated

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

The snapshot buffer is to mimic the main buffer so that when a snapshot is
needed, the snapshot and main buffer are swapped. When the snapshot buffer
is allocated, it is set to the minimal size that the ring buffer may be at
and still functional. When it is allocated it becomes the same size as the
main ring buffer, and when the main ring buffer changes in size, it should
do.

Currently, the resize only updates the snapshot buffer if it's used by the
current tracer (ie. the preemptirqsoff tracer). But it needs to be updated
anytime it is allocated.

When changing the size of the main buffer, instead of looking to see if
the current tracer is utilizing the snapshot buffer, just check if it is
allocated to know if it should be updated or not.

Also fix typo in comment just above the code change.

Cc: stable@...r.kernel.org
Fixes: ad909e21bbe69 ("tracing: Add internal tracing_snapshot() functions")
Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
---
 kernel/trace/trace.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index aa8f99f3e5de..6c79548f9574 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -6348,7 +6348,7 @@ static int __tracing_resize_ring_buffer(struct trace_array *tr,
 	if (!tr->array_buffer.buffer)
 		return 0;

-	/* Do not allow tracing while resizng ring buffer */
+	/* Do not allow tracing while resizing ring buffer */
 	tracing_stop_tr(tr);

 	ret = ring_buffer_resize(tr->array_buffer.buffer, size, cpu);
@@ -6356,7 +6356,7 @@ static int __tracing_resize_ring_buffer(struct trace_array *tr,
 		goto out_start;

 #ifdef CONFIG_TRACER_MAX_TRACE
-	if (!tr->current_trace->use_max_tr)
+	if (!tr->allocated_snapshot)
 		goto out;

 	ret = ring_buffer_resize(tr->max_buffer.buffer, size, cpu);
-- 
2.42.0