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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Ephraim Park <ephiepark@fb.com>,
        Song Liu <songliubraving@fb.com>,
        "Peter Zijlstra (Intel)" <peterz@infradead.org>, jolsa@redhat.com,
        kernel-team@fb.com,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Arnaldo Carvalho de Melo <acme@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Stephane Eranian <eranian@google.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Vince Weaver <vincent.weaver@maine.edu>,
        Ingo Molnar <mingo@kernel.org>
Subject: [PATCH 4.15 095/105] perf/core: Fix ctx_event_type in ctx_resched()
Date:   Tue, 27 Mar 2018 18:28:15 +0200
Message-Id: <20180327162803.870967820@linuxfoundation.org>
In-Reply-To: <20180327162757.813009222@linuxfoundation.org>
References: <20180327162757.813009222@linuxfoundation.org>
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4.15-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Song Liu <songliubraving@fb.com>

commit bd903afeb504db5655a45bb4cf86f38be5b1bf62 upstream.

In ctx_resched(), EVENT_FLEXIBLE should be sched_out when EVENT_PINNED is
added. However, ctx_resched() calculates ctx_event_type before checking
this condition. As a result, pinned events will NOT get higher priority
than flexible events.

The following shows this issue on an Intel CPU (where ref-cycles can
only use one hardware counter).

  1. First start:
       perf stat -C 0 -e ref-cycles  -I 1000
  2. Then, in the second console, run:
       perf stat -C 0 -e ref-cycles:D -I 1000

The second perf uses pinned events, which is expected to have higher
priority. However, because it failed in ctx_resched(). It is never
run.

This patch fixes this by calculating ctx_event_type after re-evaluating
event_type.

Reported-by: Ephraim Park <ephiepark@fb.com>
Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: <jolsa@redhat.com>
Cc: <kernel-team@fb.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Fixes: 487f05e18aa4 ("perf/core: Optimize event rescheduling on active contexts")
Link: http://lkml.kernel.org/r/20180306055504.3283731-1-songliubraving@fb.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 kernel/events/core.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -2246,7 +2246,7 @@ static void ctx_resched(struct perf_cpu_
 			struct perf_event_context *task_ctx,
 			enum event_type_t event_type)
 {
-	enum event_type_t ctx_event_type = event_type & EVENT_ALL;
+	enum event_type_t ctx_event_type;
 	bool cpu_event = !!(event_type & EVENT_CPU);
 
 	/*
@@ -2256,6 +2256,8 @@ static void ctx_resched(struct perf_cpu_
 	if (event_type & EVENT_PINNED)
 		event_type |= EVENT_FLEXIBLE;
 
+	ctx_event_type = event_type & EVENT_ALL;
+
 	perf_pmu_disable(cpuctx->ctx.pmu);
 	if (task_ctx)
 		task_ctx_sched_out(cpuctx, task_ctx, event_type);