linux-kernel - [RFC PATCH 1/3] Fix: tracepoint: static call: compare data on transition from 2->1 callees

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Date:   Tue, 27 Jul 2021 11:06:11 -0400
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Steven Rostedt <rostedt@...dmis.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Stefan Metzmacher <metze@...ba.org>
Cc:     linux-kernel@...r.kernel.org,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: [RFC PATCH 1/3] Fix: tracepoint: static call: compare data on transition from 2->1 callees

On transition from 2->1 callees, we should be comparing .data rather
than .func, because the same callback can be registered twice with
different data, and what we care about here is that the data of array
element 0 is unchanged to skip rcu sync.

[ Build tested only. ]

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
---
 kernel/tracepoint.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
index fc32821f8240..133b6454b287 100644
--- a/kernel/tracepoint.c
+++ b/kernel/tracepoint.c
@@ -338,7 +338,7 @@ static int tracepoint_remove_func(struct tracepoint *tp,
 	} else {
 		rcu_assign_pointer(tp->funcs, tp_funcs);
 		tracepoint_update_call(tp, tp_funcs,
-				       tp_funcs[0].func != old[0].func);
+				       tp_funcs[0].data != old[0].data);
 	}
 	release_probes(old);
 	return 0;
-- 
2.20.1