linux-kernel - Re: [PATCH] ftrace/direct: Fix lockup in modify_ftrace_direct

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Date:   Tue, 9 Nov 2021 11:02:37 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     Ingo Molnar <mingo@...hat.com>, lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ftrace/direct: Fix lockup in modify_ftrace_direct_multi

On Tue,  9 Nov 2021 12:42:17 +0100
Jiri Olsa <jolsa@...hat.com> wrote:

> We can't call unregister_ftrace_function under ftrace_lock.

Ouch. 

Do you have a sample module that triggers this?

I thought we had something that tested this code, but I don't see it in my
tree.

-- Steve

> 
> Fixes: ed29271894aa ("ftrace/direct: Do not disable when switching direct callers")
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> ---
>  kernel/trace/ftrace.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index b4ed1a301232..fc49e8809a56 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -5602,10 +5602,11 @@ int modify_ftrace_direct_multi(struct ftrace_ops *ops, unsigned long addr)
>  		}
>  	}
>  
> +	mutex_unlock(&ftrace_lock);
> +
>  	/* Removing the tmp_ops will add the updated direct callers to the functions */
>  	unregister_ftrace_function(&tmp_ops);
>  
> -	mutex_unlock(&ftrace_lock);
>   out_direct:
>  	mutex_unlock(&direct_mutex);
>  	return err;