linux-kernel - Re: [PATCH v3 15/19] perf: Add deferred user callchains

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Message-ID: <20241029140614.GC14555@noisy.programming.kicks-ass.net>
Date: Tue, 29 Oct 2024 15:06:14 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Josh Poimboeuf <jpoimboe@...nel.org>
Cc: x86@...nel.org, Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	linux-kernel@...r.kernel.org, Indu Bhagat <indu.bhagat@...cle.com>,
	Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>, Namhyung Kim <namhyung@...nel.org>,
	Ian Rogers <irogers@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	linux-perf-users@...r.kernel.org, Mark Brown <broonie@...nel.org>,
	linux-toolchains@...r.kernel.org, Jordan Rome <jordalgo@...a.com>,
	Sam James <sam@...too.org>, linux-trace-kernel@...r.kerne.org,
	Andrii Nakryiko <andrii.nakryiko@...il.com>,
	Jens Remus <jremus@...ux.ibm.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Florian Weimer <fweimer@...hat.com>,
	Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH v3 15/19] perf: Add deferred user callchains

On Mon, Oct 28, 2024 at 02:47:42PM -0700, Josh Poimboeuf wrote:
> diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c
> index 2278402b7ac9..eeb15ba0137f 100644
> --- a/kernel/events/callchain.c
> +++ b/kernel/events/callchain.c
> @@ -217,7 +217,7 @@ static void fixup_uretprobe_trampoline_entries(struct perf_callchain_entry *entr
>  
>  struct perf_callchain_entry *
>  get_perf_callchain(struct pt_regs *regs, bool kernel, bool user,
> -		   u32 max_stack, bool add_mark)
> +		   u32 max_stack, bool add_mark, bool defer_user)
>  {
>  	struct perf_callchain_entry *entry;
>  	struct perf_callchain_entry_ctx ctx;
> @@ -246,6 +246,15 @@ get_perf_callchain(struct pt_regs *regs, bool kernel, bool user,
>  			regs = task_pt_regs(current);
>  		}
>  
> +		if (defer_user) {
> +			/*
> +			 * Foretell the coming of PERF_RECORD_CALLCHAIN_DEFERRED
> +			 * which can be stitched to this one.
> +			 */
> +			perf_callchain_store_context(&ctx, PERF_CONTEXT_USER_DEFERRED);
> +			goto exit_put;
> +		}
> +
>  		if (add_mark)
>  			perf_callchain_store_context(&ctx, PERF_CONTEXT_USER);

Given that the whole deferred thing doesn't handle COMPAT, this will
break thing, no?