linux-kernel - Re: [PATCH] ring-buffer: Fix memory leak of free page

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Message-Id: <20231211212319.d1a714d0139e4fd893183b9e@kernel.org>
Date:   Mon, 11 Dec 2023 21:23:19 +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>,
        Mark Rutland <mark.rutland@....com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: Re: [PATCH] ring-buffer: Fix memory leak of free page

On Sun, 10 Dec 2023 22:12:50 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:

> From: "Steven Rostedt (Google)" <rostedt@...dmis.org>
> 
> Reading the ring buffer does a swap of a sub-buffer within the ring buffer
> with a empty sub-buffer. This allows the reader to have full access to the
> content of the sub-buffer that was swapped out without having to worry
> about contention with the writer.
> 
> The readers call ring_buffer_alloc_read_page() to allocate a page that
> will be used to swap with the ring buffer. When the code is finished with
> the reader page, it calls ring_buffer_free_read_page(). Instead of freeing
> the page, it stores it as a spare. Then next call to
> ring_buffer_alloc_read_page() will return this spare instead of calling
> into the memory management system to allocate a new page.
> 
> Unfortunately, on freeing of the ring buffer, this spare page is not
> freed, and causes a memory leak.
> 

Oops, Looks good to me.

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

Thanks,

> Cc: stable@...r.kernel.org
> Fixes: 73a757e63114d ("ring-buffer: Return reader page back into existing ring buffer")
> Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
> ---
>  kernel/trace/ring_buffer.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> index a38e5a3c6803..dd37d21d6e55 100644
> --- a/kernel/trace/ring_buffer.c
> +++ b/kernel/trace/ring_buffer.c
> @@ -1790,6 +1790,8 @@ static void rb_free_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
>  		free_buffer_page(bpage);
>  	}
>  
> +	free_page((unsigned long)cpu_buffer->free_page);
> +
>  	kfree(cpu_buffer);
>  }
>  
> -- 
> 2.42.0
> 


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