linux-kernel - Re: [PATCH 1/4] rethook: use preempt_{disable, enable}_notrace in rethook_trampoline

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Message-Id: <20230516132502.c51be728bd086b8c9005ce57@kernel.org>
Date:   Tue, 16 May 2023 13:25:02 +0900
From:   Masami Hiramatsu (Google) <mhiramat@...nel.org>
To:     Ze Gao <zegao2021@...il.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>, Ze Gao <zegao@...cent.com>,
        linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] rethook: use preempt_{disable, enable}_notrace in
 rethook_trampoline_handler

Hi Ze Gao,

Thanks for the patch.

On Mon, 15 May 2023 11:26:38 +0800
Ze Gao <zegao2021@...il.com> wrote:

> This patch replace preempt_{disable, enable} with its corresponding
> notrace version in rethook_trampoline_handler so no worries about stack
> recursion or overflow introduced by preempt_count_{add, sub} under
> fprobe + rethook context.

So, have you ever see that recursion of preempt_count overflow case?

I intended to use the normal preempt_disable() here because it does NOT
prohibit any function-trace call (Note that both kprobes and
fprobe checks recursive call by itself) but it is used for preempt_onoff
tracer.

Thanks,

> 
> Signed-off-by: Ze Gao <zegao@...cent.com>
> ---
>  kernel/trace/rethook.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/trace/rethook.c b/kernel/trace/rethook.c
> index 32c3dfdb4d6a..60f6cb2b486b 100644
> --- a/kernel/trace/rethook.c
> +++ b/kernel/trace/rethook.c
> @@ -288,7 +288,7 @@ unsigned long rethook_trampoline_handler(struct pt_regs *regs,
>  	 * These loops must be protected from rethook_free_rcu() because those
>  	 * are accessing 'rhn->rethook'.
>  	 */
> -	preempt_disable();
> +	preempt_disable_notrace();
>  
>  	/*
>  	 * Run the handler on the shadow stack. Do not unlink the list here because
> @@ -321,7 +321,7 @@ unsigned long rethook_trampoline_handler(struct pt_regs *regs,
>  		first = first->next;
>  		rethook_recycle(rhn);
>  	}
> -	preempt_enable();
> +	preempt_enable_notrace();
>  
>  	return correct_ret_addr;
>  }
> -- 
> 2.40.1
> 


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