linux-kernel - Re: [PATCH v5 11/17] perf: Simplify get_perf

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Message-ID: <20250424163607.GE18306@noisy.programming.kicks-ass.net>
Date: Thu, 24 Apr 2025 18:36:07 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Josh Poimboeuf <jpoimboe@...nel.org>, x86@...nel.org,
	Ingo Molnar <mingo@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Indu Bhagat <indu.bhagat@...cle.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>,
	Andrii Nakryiko <andrii.nakryiko@...il.com>,
	Jens Remus <jremus@...ux.ibm.com>,
	Florian Weimer <fweimer@...hat.com>,
	Andy Lutomirski <luto@...nel.org>, Weinan Liu <wnliu@...gle.com>,
	Blake Jones <blakejones@...gle.com>,
	Beau Belgrave <beaub@...ux.microsoft.com>,
	"Jose E. Marchesi" <jemarch@....org>
Subject: Re: [PATCH v5 11/17] perf: Simplify get_perf_callchain() user logic

On Thu, Apr 24, 2025 at 12:25:40PM -0400, Steven Rostedt wrote:
> From: Josh Poimboeuf <jpoimboe@...nel.org>
> 
> Simplify the get_perf_callchain() user logic a bit.  task_pt_regs()
> should never be NULL.
> 
> Acked-by: Namhyung Kim <namhyung@...nel.org>
> Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
> Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
> ---
>  kernel/events/callchain.c | 20 +++++++++-----------
>  1 file changed, 9 insertions(+), 11 deletions(-)
> 
> diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c
> index abf258913ab6..bba7f8540ade 100644
> --- a/kernel/events/callchain.c
> +++ b/kernel/events/callchain.c
> @@ -246,22 +246,20 @@ get_perf_callchain(struct pt_regs *regs, bool kernel, bool user,
>  
>  	if (user) {
>  		if (!user_mode(regs)) {
> -			if  (current->mm)
> -				regs = task_pt_regs(current);
> -			else
> -				regs = NULL;
> +			if (!current->mm)
> +				goto exit_put;
> +			regs = task_pt_regs(current);

I'm thinking this might be one of those is-kthread test written as
has-mm, and they're broken.

Notably things like the io-uring kthreads do have mm.

>  		}
>  
> -		if (regs) {
> -			if (add_mark)
> -				perf_callchain_store_context(&ctx, PERF_CONTEXT_USER);
> +		if (add_mark)
> +			perf_callchain_store_context(&ctx, PERF_CONTEXT_USER);
>  
> -			start_entry_idx = entry->nr;
> -			perf_callchain_user(&ctx, regs);
> -			fixup_uretprobe_trampoline_entries(entry, start_entry_idx);
> -		}
> +		start_entry_idx = entry->nr;
> +		perf_callchain_user(&ctx, regs);
> +		fixup_uretprobe_trampoline_entries(entry, start_entry_idx);
>  	}
>  
> +exit_put:
>  	put_callchain_entry(rctx);
>  
>  	return entry;
> -- 
> 2.47.2
> 
>