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Message-ID: <20250424163845.GG18306@noisy.programming.kicks-ass.net>
Date: Thu, 24 Apr 2025 18:38:45 +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 13/17] perf: Support deferred user callchains
On Thu, Apr 24, 2025 at 12:25:42PM -0400, Steven Rostedt wrote:
> +static int deferred_request(struct perf_event *event)
> +{
> + struct callback_head *work = &event->pending_unwind_work;
> + int pending;
> + int ret;
> +
> + if (!current->mm || !user_mode(task_pt_regs(current)))
> + return -EINVAL;
> +
> + if (in_nmi())
> + return deferred_request_nmi(event);
> +
> + guard(irqsave)();
> +
> + /* callback already pending? */
> + pending = READ_ONCE(event->pending_unwind_callback);
> + if (pending)
> + return 1;
> +
> + /* Claim the work unless an NMI just now swooped in to do so. */
> + if (!try_cmpxchg(&event->pending_unwind_callback, &pending, 1))
> + return 1;
> +
> + /* The work has been claimed, now schedule it. */
> + ret = task_work_add(current, work, TWA_RESUME);
> + if (WARN_ON_ONCE(ret)) {
> + WRITE_ONCE(event->pending_unwind_callback, 0);
> + return ret;
> + }
> + return 0;
> +}
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