linux-kernel - [PATCH v2] perf: fix perf_event

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Message-ID: <20230313171608.298734-1-song@kernel.org>
Date:   Mon, 13 Mar 2023 10:16:08 -0700
From:   Song Liu <song@...nel.org>
To:     <linux-kernel@...r.kernel.org>
CC:     <kernel-team@...a.com>, Song Liu <song@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Namhyung Kim <namhyung@...nel.org>
Subject: [PATCH v2] perf: fix perf_event_context->time

Time readers rely on perf_event_context->[time|timestamp|timeoffset] to get
accurate time_enabled and time_running for an event. The difference between
ctx->timestamp and ctx->time is the among of time when the context is not
enabled. __update_context_time(ctx, false) is used to increase timestamp,
but not time. Therefore, it should only be called in ctx_sched_in() when
EVENT_TIME was not enabled.

Fixes: 09f5e7dc7ad7 ("perf: Fix perf_event_read_local() time")
Cc: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Namhyung Kim <namhyung@...nel.org>
Acked-by: Namhyung Kim <namhyung@...nel.org>
Signed-off-by: Song Liu <song@...nel.org>
---
 kernel/events/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 380476a934e8..67478f43e26e 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3872,7 +3872,7 @@ ctx_sched_in(struct perf_event_context *ctx, enum event_type_t event_type)
 	if (likely(!ctx->nr_events))
 		return;
 
-	if (is_active ^ EVENT_TIME) {
+	if (!(is_active & EVENT_TIME)) {
 		/* start ctx time */
 		__update_context_time(ctx, false);
 		perf_cgroup_set_timestamp(cpuctx);
-- 
2.34.1