From: Steven Rostedt <rostedt@goodmis.org>

The pages_touched field represents the number of subbuffers in the ring
buffer that have content that can be read. This is used in accounting of
"dirty_pages" and "buffer_percent" to allow the user to wait for the
buffer to be filled to a certain amount before it reads the buffer in
blocking mode.

The persistent buffer never updated this value so it was set to zero, and
this accounting would take it as it had no content. This would cause user
space to wait for content even though there's enough content in the ring
buffer that satisfies the buffer_percent.

Cc: stable@vger.kernel.org
Fixes: 5f3b6e839f3ce ("ring-buffer: Validate boot range memory events")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 kernel/trace/ring_buffer.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 0419d41a2060..bb6089c2951e 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -1850,6 +1850,11 @@ static void rb_meta_validate_events(struct ring_buffer_per_cpu *cpu_buffer)
 				cpu_buffer->cpu);
 			goto invalid;
 		}
+
+		/* If the buffer has content, update pages_touched */
+		if (ret)
+			local_inc(&cpu_buffer->pages_touched);
+
 		entries += ret;
 		entry_bytes += local_read(&head_page->page->commit);
 		local_set(&cpu_buffer->head_page->entries, ret);
-- 
2.47.2

On Fri, 14 Feb 2025 12:35:12 -0500
Steven Rostedt <rostedt@goodmis.org> wrote:

> From: Steven Rostedt <rostedt@goodmis.org>
> 
> The pages_touched field represents the number of subbuffers in the ring
> buffer that have content that can be read. This is used in accounting of
> "dirty_pages" and "buffer_percent" to allow the user to wait for the
> buffer to be filled to a certain amount before it reads the buffer in
> blocking mode.
> 
> The persistent buffer never updated this value so it was set to zero, and
> this accounting would take it as it had no content. This would cause user
> space to wait for content even though there's enough content in the ring
> buffer that satisfies the buffer_percent.

Looks good to me.

Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Thanks,

> 
> Cc: stable@vger.kernel.org
> Fixes: 5f3b6e839f3ce ("ring-buffer: Validate boot range memory events")
> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
> ---
>  kernel/trace/ring_buffer.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> index 0419d41a2060..bb6089c2951e 100644
> --- a/kernel/trace/ring_buffer.c
> +++ b/kernel/trace/ring_buffer.c
> @@ -1850,6 +1850,11 @@ static void rb_meta_validate_events(struct ring_buffer_per_cpu *cpu_buffer)
>  				cpu_buffer->cpu);
>  			goto invalid;
>  		}
> +
> +		/* If the buffer has content, update pages_touched */
> +		if (ret)
> +			local_inc(&cpu_buffer->pages_touched);
> +
>  		entries += ret;
>  		entry_bytes += local_read(&head_page->page->commit);
>  		local_set(&cpu_buffer->head_page->entries, ret);
> -- 
> 2.47.2
> 


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>