linux-kernel - Re: [PATCH v1] kernel/trace/ring_buffer: don't deactivate non-existant pages

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Date:   Thu, 17 Nov 2022 17:11:46 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Daniil Tatianin <d-tatianin@...dex-team.ru>
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        linux-kernel@...r.kernel.org, lvc-project@...uxtesting.org,
        yc-core@...dex-team.ru
Subject: Re: [PATCH v1] kernel/trace/ring_buffer: don't deactivate
 non-existant pages

On Mon, 14 Nov 2022 17:31:29 +0300
Daniil Tatianin <d-tatianin@...dex-team.ru> wrote:

> rb_head_page_deactivate() expects cpu_buffer to contain a valid list of
> ->pages, so verify that the list is actually present before calling it.  
> 
> Found by Linux Verification Center (linuxtesting.org) with the SVACE
> static analysis tool.
> 
> Signed-off-by: Daniil Tatianin <d-tatianin@...dex-team.ru>
> ---
>  kernel/trace/ring_buffer.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> index a12e27815555..1e9de3d49701 100644
> --- a/kernel/trace/ring_buffer.c
> +++ b/kernel/trace/ring_buffer.c
> @@ -1635,9 +1635,9 @@ static void rb_free_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
>  
>  	free_buffer_page(cpu_buffer->reader_page);
>  
> -	rb_head_page_deactivate(cpu_buffer);
> -

Logically, this should never happen, but regardless, I consider this a fix.

Queued. Thanks Daniil!

-- Steve


>  	if (head) {
> +		rb_head_page_deactivate(cpu_buffer);
> +
>  		list_for_each_entry_safe(bpage, tmp, head, list) {
>  			list_del_init(&bpage->list);
>  			free_buffer_page(bpage);