linux-kernel - Re: [PATCH v2] fprobe: add unlock to match a succeeded ftrace_test_recursion

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Date:   Thu, 6 Jul 2023 12:09:16 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Ze Gao <zegao2021@...il.com>
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        Ze Gao <zegao@...cent.com>, Yafang <laoar.shao@...il.com>
Subject: Re: [PATCH v2] fprobe: add unlock to match a succeeded
 ftrace_test_recursion_trylock

On Mon,  3 Jul 2023 17:23:36 +0800
Ze Gao <zegao2021@...il.com> wrote:

> Unlock ftrace recursion lock when fprobe_kprobe_handler() is failed
> because of some running kprobe.
> 
> Fixes: 3cc4e2c5fbae ("fprobe: make fprobe_kprobe_handler recursion free")
> Reported-by: Yafang <laoar.shao@...il.com>
> Closes: https://lore.kernel.org/linux-trace-kernel/CALOAHbC6UpfFOOibdDiC7xFc5YFUgZnk3MZ=3Ny6we=AcrNbew@mail.gmail.com/
> Signed-off-by: Ze Gao <zegao@...cent.com>

Reviewed-by: Steven Rostedt (Google) <rostedt@...dmis.org>

> ---
>  kernel/trace/fprobe.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c
> index 18d36842faf5..93b3e361bb97 100644
> --- a/kernel/trace/fprobe.c
> +++ b/kernel/trace/fprobe.c
> @@ -102,12 +102,14 @@ static void fprobe_kprobe_handler(unsigned long ip, unsigned long parent_ip,
>  
>  	if (unlikely(kprobe_running())) {

Off topic for this patch, but Masami, what's the purpose of not calling the
fprobe when a kprobe is running? Does that mean it has probed another kprobe?

Probably could add a comment here to explain the issue.

-- Steve


>  		fp->nmissed++;
> -		return;
> +		goto recursion_unlock;
>  	}
>  
>  	kprobe_busy_begin();
>  	__fprobe_handler(ip, parent_ip, ops, fregs);
>  	kprobe_busy_end();
> +
> +recursion_unlock:
>  	ftrace_test_recursion_unlock(bit);
>  }
>