linux-kernel - Re: [PATCH] ring-buffer: Fix refcount setting of boot mapped buffers

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Message-Id: <20241012142054.bc1fffb7b4829ff2e496e566@kernel.org>
Date: Sat, 12 Oct 2024 14:20:54 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: LKML <linux-kernel@...r.kernel.org>, Linux Trace Kernel
 <linux-trace-kernel@...r.kernel.org>, Masami Hiramatsu
 <mhiramat@...nel.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: Re: [PATCH] ring-buffer: Fix refcount setting of boot mapped
 buffers

On Fri, 11 Oct 2024 16:52:24 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> From: Steven Rostedt <rostedt@...dmis.org>
> 
> A ring buffer which has its buffered mapped at boot up to fixed memory
> should not be freed. Other buffers can be. The ref counting setup was
> wrong for both. It made the not mapped buffers ref count have zero, and the
> boot mapped buffer a ref count of 1. But an normally allocated buffer
> should be 1, where it can be removed.
> 
> Keep the ref count of a normal boot buffer with its setup ref count (do
> not decrement it), and increment the fixed memory boot mapped buffer's ref
> count.
> 

Looks good to me.

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

Thank you,

> Fixes: e645535a954ad ("tracing: Add option to use memmapped memory for trace boot instance")
> Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
> ---
>  kernel/trace/trace.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index c01375adc471..5ba40f39c8b5 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -10610,10 +10610,10 @@ __init static void enable_instances(void)
>  		 * cannot be deleted by user space, so keep the reference
>  		 * to it.
>  		 */
> -		if (start)
> +		if (start) {
>  			tr->flags |= TRACE_ARRAY_FL_BOOT;
> -		else
> -			trace_array_put(tr);
> +			tr->ref++;
> +		}
>  
>  		while ((tok = strsep(&curr_str, ","))) {
>  			early_enable_events(tr, tok, true);
> -- 
> 2.45.2
> 


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