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Date:   Tue, 19 Nov 2019 13:14:29 +0100
From:   Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To:     linux-kernel@vger.kernel.org,
        Joel Fernandes <joel@joelfernandes.org>,
        "Paul E. McKenney" <paulmck@linux.ibm.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@redhat.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>
Subject: [PATCH] perf/core: Add SRCU annotation for pmus list walk
Message-ID: <20191119121429.zhcubzdhm672zasg@linutronix.de>
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Sender: linux-kernel-owner@vger.kernel.org
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Since commit
   28875945ba98d ("rcu: Add support for consolidated-RCU reader checking")

there is an additional check to ensure that a RCU related lock is held
while the RCU list is iterated.
This section holds the SRCU reader lock instead.

Add annotation to list_for_each_entry_rcu() that pmus_srcu must be
acquired during the list traversal.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---

I see the warning in in v5.4-rc during boot. For some reason I don't see
it in tip/master during boot but "perf stat w" triggers it again (among
other things).

 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 5224388872069..dbb3b26a55612 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -10497,7 +10497,7 @@ static struct pmu *perf_init_event(struct perf_event *event)
 		goto unlock;
 	}
 
-	list_for_each_entry_rcu(pmu, &pmus, entry) {
+	list_for_each_entry_rcu(pmu, &pmus, entry, lockdep_is_held(&pmus_srcu)) {
 		ret = perf_try_init_event(pmu, event);
 		if (!ret)
 			goto unlock;
-- 
2.24.0