[PATCH v2 01/11] ring-buffer: Allow mapped field to be set without mapping

[Steven Rostedt]

From: "Steven Rostedt (Google)" <rost...@goodmis.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) <rost...@goodmis.org>
---
 kernel/trace/ring_buffer.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 793ecc454039..44b1d5f1a99a 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -5223,6 +5223,9 @@ 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;
@@ -6167,7 +6170,7 @@ 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);
        }
@@ -6345,12 +6348,13 @@ 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);
+
        raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
 
        err = __rb_map_vma(cpu_buffer, vma);
        if (!err) {
                raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
-               cpu_buffer->mapped = 1;
+               cpu_buffer->mapped++;
                raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
        } else {
                kfree(cpu_buffer->subbuf_ids);
@@ -6388,7 +6392,7 @@ int ring_buffer_unmap(struct trace_buffer *buffer, int 
cpu)
        mutex_lock(&buffer->mutex);
        raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
 
-       cpu_buffer->mapped = 0;
+       cpu_buffer->mapped--;
 
        raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
 
-- 
2.43.0