linux-kernel - Re: [PATCH perf/core 08/22] uprobes/x86: Add mapping for optimized uprobe trampolines

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Message-ID: <20250427180432.GC27775@redhat.com>
Date: Sun, 27 Apr 2025 20:04:32 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Jiri Olsa <jolsa@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>,
	Andrii Nakryiko <andrii@...nel.org>, bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
	x86@...nel.org, Song Liu <songliubraving@...com>,
	Yonghong Song <yhs@...com>,
	John Fastabend <john.fastabend@...il.com>,
	Hao Luo <haoluo@...gle.com>, Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Alan Maguire <alan.maguire@...cle.com>,
	David Laight <David.Laight@...LAB.COM>,
	Thomas Weißschuh <thomas@...ch.de>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH perf/core 08/22] uprobes/x86: Add mapping for optimized
 uprobe trampolines

On 04/21, Jiri Olsa wrote:
>
> +struct uprobe_trampoline {
> +	struct hlist_node	node;
> +	unsigned long		vaddr;
> +	atomic64_t		ref;
> +};

I don't really understand the point of uprobe_trampoline->ref...

set_orig_insn/swbp_unoptimize paths don't call uprobe_trampoline_put().
It is only called in unlikely case when swbp_optimize() fails, so perhaps
we can kill this member and uprobe_trampoline_put() ? At least in the initial
version.

> +static void uprobe_trampoline_put(struct uprobe_trampoline *tramp)
> +{
> +	if (tramp && atomic64_dec_and_test(&tramp->ref))
> +		destroy_uprobe_trampoline(tramp);
> +}

Why does it check tramp != NULL ?

Oleg.