linux-kernel - [PATCH 2/2] events: callchain: Use RCU API to access RCU pointer

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Date:   Wed, 29 Jan 2020 21:38:13 +0530
From:   Amol Grover <frextrite@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        Joel Fernandes <joel@...lfernandes.org>,
        Madhuparna Bhowmik <madhuparnabhowmik04@...il.com>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Amol Grover <frextrite@...il.com>
Subject: [PATCH 2/2] events: callchain: Use RCU API to access RCU pointer

callchain_cpus_entries is annotated as an RCU pointer.
Hence rcu_dereference_protected or similar RCU API is
required to dereference the pointer.

This fixes the following sparse warning
kernel/events/callchain.c:65:17: warning: incorrect type in assignment

Signed-off-by: Amol Grover <frextrite@...il.com>
---
 kernel/events/callchain.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c
index f91e1f41d25d..a672d02a1b3a 100644
--- a/kernel/events/callchain.c
+++ b/kernel/events/callchain.c
@@ -62,7 +62,8 @@ static void release_callchain_buffers(void)
 {
 	struct callchain_cpus_entries *entries;
 
-	entries = callchain_cpus_entries;
+	entries = rcu_dereference_protected(callchain_cpus_entries,
+					    lockdep_is_held(&callchain_mutex));
 	RCU_INIT_POINTER(callchain_cpus_entries, NULL);
 	call_rcu(&entries->rcu_head, release_callchain_buffers_rcu);
 }
-- 
2.24.1