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

[Steven Rostedt]

From: "Steven Rostedt (Google)" <rostedt@xxxxxxxxxxx>

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@xxxxxxxxxxx>
---
 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