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

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Message-Id: <20210805132717.23813-2-mathieu.desnoyers@efficios.com>
Date:   Thu,  5 Aug 2021 09:27:15 -0400
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Stefan Metzmacher <metze@...ba.org>, stable@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: [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.

Link: https://lore.kernel.org/io-uring/4ebea8f0-58c9-e571-fd30-0ce4f6f09c70@samba.org/
Fixes: d25e37d89dd2 ("tracepoint: Optimize using static_call()")
Fixes: 547305a64632 ("tracepoint: Fix out of sync data passing by static caller")
Fixes: 352384d5c84e ("tracepoints: Update static_call before tp_funcs when adding a tracepoint")
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: "Paul E. McKenney" <paulmck@...nel.org>
Cc: Stefan Metzmacher <metze@...ba.org>
Cc: <stable@...r.kernel.org> # 5.10+
---
 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;
-- 
2.17.1