[PATCH v6 01/13] ring-buffer: Allow mapped field to be set without mapping

Steven Rostedt
2024-06-12T23:20:06Z

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@goodmis.org>
---
kernel/trace/ring_buffer.c | 37 +++++++++++++++++++++++++++----------
1 file changed, 27 insertions(+), 10 deletions(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 28853966aa9a..a240bdc0f2d8 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -491,6 +491,7 @@ struct ring_buffer_per_cpu {
unsigned long pages_removed;

unsigned int mapped;
+ unsigned int user_mapped; /* user space mapping */
struct mutex mapping_lock;
unsigned long *subbuf_ids; /* ID to subbuf VA */
struct trace_buffer_meta *meta_page;
@@ -5224,6 +5225,9 @@ 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;
@@ -5280,7 +5284,7 @@ rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
cpu_buffer->lost_events = 0;
cpu_buffer->last_overrun = 0;

- if (cpu_buffer->mapped)
+ if (cpu_buffer->user_mapped)
rb_update_meta_page(cpu_buffer);

rb_head_page_activate(cpu_buffer);
@@ -6167,7 +6171,7 @@ rb_get_mapped_buffer(struct trace_buffer *buffer, int cpu)

mutex_lock(&cpu_buffer->mapping_lock);

- if (!cpu_buffer->mapped) {
+ if (!cpu_buffer->user_mapped) {
mutex_unlock(&cpu_buffer->mapping_lock);
return ERR_PTR(-ENODEV);
}
@@ -6191,19 +6195,26 @@ static int __rb_inc_dec_mapped(struct ring_buffer_per_cpu *cpu_buffer,

lockdep_assert_held(&cpu_buffer->mapping_lock);

+ /* mapped is always greater or equal to user_mapped */
+ if (WARN_ON(cpu_buffer->mapped < cpu_buffer->user_mapped))
+ return -EINVAL;
+
if (inc && cpu_buffer->mapped == UINT_MAX)
return -EBUSY;

- if (WARN_ON(!inc && cpu_buffer->mapped == 0))
+ if (WARN_ON(!inc && cpu_buffer->user_mapped == 0))
return -EINVAL;

mutex_lock(&cpu_buffer->buffer->mutex);
raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);

- if (inc)
+ if (inc) {
+ cpu_buffer->user_mapped++;
cpu_buffer->mapped++;
- else
+ } else {
+ cpu_buffer->user_mapped--;
cpu_buffer->mapped--;
+ }

raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
mutex_unlock(&cpu_buffer->buffer->mutex);
@@ -6328,7 +6339,7 @@ int ring_buffer_map(struct trace_buffer *buffer, int cpu,

mutex_lock(&cpu_buffer->mapping_lock);

- if (cpu_buffer->mapped) {
+ if (cpu_buffer->user_mapped) {
err = __rb_map_vma(cpu_buffer, vma);
if (!err)
err = __rb_inc_dec_mapped(cpu_buffer, true);
@@ -6359,12 +6370,15 @@ 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;
+ /* This is the first time it is mapped by user */
+ cpu_buffer->mapped++;
+ cpu_buffer->user_mapped = 1;
raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
} else {
kfree(cpu_buffer->subbuf_ids);
@@ -6392,10 +6406,10 @@ int ring_buffer_unmap(struct trace_buffer *buffer, int cpu)

mutex_lock(&cpu_buffer->mapping_lock);

- if (!cpu_buffer->mapped) {
+ if (!cpu_buffer->user_mapped) {
err = -ENODEV;
goto out;
- } else if (cpu_buffer->mapped > 1) {
+ } else if (cpu_buffer->user_mapped > 1) {
__rb_inc_dec_mapped(cpu_buffer, false);
goto out;
}
@@ -6403,7 +6417,10 @@ 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;
+ /* This is the last user space mapping */
+ if (!WARN_ON_ONCE(cpu_buffer->mapped < cpu_buffer->user_mapped))
+ cpu_buffer->mapped--;
+ cpu_buffer->user_mapped = 0;

raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);

--
2.43.0