linux-kernel - Re: [PATCH v2 04/10] ftrace: Store direct called addresses in their ops

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Message-ID: <20230315194334.58eb56ab@gandalf.local.home>
Date:   Wed, 15 Mar 2023 19:43:34 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Florent Revest <revest@...omium.org>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-trace-kernel@...r.kernel.org, bpf@...r.kernel.org,
        catalin.marinas@....com, will@...nel.org, mhiramat@...nel.org,
        mark.rutland@....com, ast@...nel.org, daniel@...earbox.net,
        andrii@...nel.org, kpsingh@...nel.org, jolsa@...nel.org,
        xukuohai@...weicloud.com, lihuafei1@...wei.com
Subject: Re: [PATCH v2 04/10] ftrace: Store direct called addresses in their
 ops

On Tue,  7 Feb 2023 19:21:29 +0100
Florent Revest <revest@...omium.org> wrote:

> @@ -5445,6 +5445,7 @@ __modify_ftrace_direct(struct ftrace_ops *ops, unsigned long addr)
>  	/* Enable the tmp_ops to have the same functions as the direct ops */
>  	ftrace_ops_init(&tmp_ops);
>  	tmp_ops.func_hash = ops->func_hash;
> +	tmp_ops.direct_call = addr;
>  
>  	err = register_ftrace_function_nolock(&tmp_ops);
>  	if (err)
> @@ -5466,6 +5467,7 @@ __modify_ftrace_direct(struct ftrace_ops *ops, unsigned long addr)
>  			entry->direct = addr;
>  		}
>  	}
> +	WRITE_ONCE(ops->direct_call, addr);

I'm curious about the use of WRITE_ONCE(). It should not go outside the
mutex barrier.

-- Steve

>  
>  	mutex_unlock(&ftrace_lock);
>