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Date: Fri,  7 Jun 2024 13:47:27 -0700
Message-Id: <20240607204727.849174-1-irogers@google.com>
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Subject: [PATCH v1] perf record: Ensure space for lost samples
From: Ian Rogers <irogers@google.com>
To: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>, 
	Arnaldo Carvalho de Melo <acme@kernel.org>, Namhyung Kim <namhyung@kernel.org>, 
	Mark Rutland <mark.rutland@arm.com>, 
	Alexander Shishkin <alexander.shishkin@linux.intel.com>, Jiri Olsa <jolsa@kernel.org>, 
	Ian Rogers <irogers@google.com>, Adrian Hunter <adrian.hunter@intel.com>, 
	Kan Liang <kan.liang@linux.intel.com>, linux-perf-users@vger.kernel.org, 
	linux-kernel@vger.kernel.org
Cc: Milian Wolff <milian.wolff@kdab.com>
Content-Type: text/plain; charset="UTF-8"

Previous allocation didn't account for sample ID written after the
lost samples event. Switch from malloc/free to a stack allocation.

Reported-by: Milian Wolff <milian.wolff@kdab.com>
Closes: https://lore.kernel.org/linux-perf-users/23879991.0LEYPuXRzz@milian-workstation/
Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/lib/perf/include/perf/event.h |  3 +++
 tools/perf/builtin-record.c         | 37 ++++++++++-------------------
 2 files changed, 15 insertions(+), 25 deletions(-)

diff --git a/tools/lib/perf/include/perf/event.h b/tools/lib/perf/include/perf/event.h
index ae64090184d3..8f3cefef9069 100644
--- a/tools/lib/perf/include/perf/event.h
+++ b/tools/lib/perf/include/perf/event.h
@@ -77,6 +77,9 @@ struct perf_record_lost_samples {
 	__u64			 lost;
 };
 
+#define MAX_ID_HDR_ENTRIES  6
+#define PERF_RECORD_MAX_LOST_SAMPLE_AND_ID_SIZE \
+	(sizeof(struct perf_record_lost_samples) + MAX_ID_HDR_ENTRIES * sizeof(__u64))
 /*
  * PERF_FORMAT_ENABLED | PERF_FORMAT_RUNNING | PERF_FORMAT_ID | PERF_FORMAT_LOST
  */
diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index 66a3de8ac661..1615a1723fb9 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -1926,7 +1926,10 @@ static void __record__save_lost_samples(struct record *rec, struct evsel *evsel,
 static void record__read_lost_samples(struct record *rec)
 {
 	struct perf_session *session = rec->session;
-	struct perf_record_lost_samples *lost = NULL;
+	union {
+		struct perf_record_lost_samples lost;
+		char lost_and_sample_id[PERF_RECORD_MAX_LOST_SAMPLE_AND_ID_SIZE];
+	} lost;
 	struct evsel *evsel;
 
 	/* there was an error during record__open */
@@ -1951,20 +1954,13 @@ static void record__read_lost_samples(struct record *rec)
 
 				if (perf_evsel__read(&evsel->core, x, y, &count) < 0) {
 					pr_debug("read LOST count failed\n");
-					goto out;
+					return;
 				}
 
 				if (count.lost) {
-					if (!lost) {
-						lost = zalloc(sizeof(*lost) +
-							      session->machines.host.id_hdr_size);
-						if (!lost) {
-							pr_debug("Memory allocation failed\n");
-							return;
-						}
-						lost->header.type = PERF_RECORD_LOST_SAMPLES;
-					}
-					__record__save_lost_samples(rec, evsel, lost,
+					memset(&lost, 0, sizeof(lost));
+					lost.lost.header.type = PERF_RECORD_LOST_SAMPLES;
+					__record__save_lost_samples(rec, evsel, &lost.lost,
 								    x, y, count.lost, 0);
 				}
 			}
@@ -1972,21 +1968,12 @@ static void record__read_lost_samples(struct record *rec)
 
 		lost_count = perf_bpf_filter__lost_count(evsel);
 		if (lost_count) {
-			if (!lost) {
-				lost = zalloc(sizeof(*lost) +
-					      session->machines.host.id_hdr_size);
-				if (!lost) {
-					pr_debug("Memory allocation failed\n");
-					return;
-				}
-				lost->header.type = PERF_RECORD_LOST_SAMPLES;
-			}
-			__record__save_lost_samples(rec, evsel, lost, 0, 0, lost_count,
+			memset(&lost, 0, sizeof(lost));
+			lost.lost.header.type = PERF_RECORD_LOST_SAMPLES;
+			__record__save_lost_samples(rec, evsel, &lost.lost, 0, 0, lost_count,
 						    PERF_RECORD_MISC_LOST_SAMPLES_BPF);
 		}
 	}
-out:
-	free(lost);
 }
 
 static volatile sig_atomic_t workload_exec_errno;
@@ -3198,7 +3185,7 @@ static int switch_output_setup(struct record *rec)
 	unsigned long val;
 
 	/*
-	 * If we're using --switch-output-events, then we imply its 
+	 * If we're using --switch-output-events, then we imply its
 	 * --switch-output=signal, as we'll send a SIGUSR2 from the side band
 	 *  thread to its parent.
 	 */
-- 
2.45.2.505.gda0bf45e8d-goog