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Message-ID: <ZcaUw4xQT0VcC7IO@tassilo>
Date: Fri, 9 Feb 2024 13:10:27 -0800
From: Andi Kleen <ak@...ux.intel.com>
To: Adrian Hunter <adrian.hunter@...el.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Heiko Carstens <hca@...ux.ibm.com>,
Thomas Richter <tmricht@...ux.ibm.com>,
Hendrik Brueckner <brueckner@...ux.ibm.com>,
Suzuki K Poulose <suzuki.poulose@....com>,
Mike Leach <mike.leach@...aro.org>,
James Clark <james.clark@....com>, coresight@...ts.linaro.org,
linux-arm-kernel@...ts.infradead.org,
Yicong Yang <yangyicong@...ilicon.com>,
Jonathan Cameron <jonathan.cameron@...wei.com>,
Will Deacon <will@...nel.org>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Jiri Olsa <jolsa@...nel.org>, Namhyung Kim <namhyung@...nel.org>,
Ian Rogers <irogers@...gle.com>, linux-kernel@...r.kernel.org,
linux-perf-users@...r.kernel.org
Subject: Re: [PATCH V5 01/12] perf/core: Add aux_pause, aux_resume,
aux_start_paused
> The writes to rb->aux_in_pause_resume must be done
> only once. It might be possible to get away without
> WRITE_ONCE(), but really the compiler should be informed
> not to make assumptions.
What stops the NMI from firing here?
> >> + if (READ_ONCE(rb->aux_in_pause_resume))
> >> + /* Guard against NMI, NMI loses here */
> >> + goto out_restore;
<----------------------- NMI
> >> + WRITE_ONCE(rb->aux_in_pause_resume, 1);
Even if it isn't racy it needs a clear comment.
-Andi
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