linux-kernel - [PATCH AUTOSEL 4.14 6/6] ring-buffer: Do not record in NMI if the arch does not support cmpxchg in NMI

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Date: Mon, 18 Dec 2023 07:47:23 -0500
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: "Steven Rostedt (Google)" <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Sasha Levin <sashal@...nel.org>,
	linux-trace-kernel@...r.kernel.org
Subject: [PATCH AUTOSEL 4.14 6/6] ring-buffer: Do not record in NMI if the arch does not support cmpxchg in NMI

From: "Steven Rostedt (Google)" <rostedt@...dmis.org>

[ Upstream commit 712292308af2265cd9b126aedfa987f10f452a33 ]

As the ring buffer recording requires cmpxchg() to work, if the
architecture does not support cmpxchg in NMI, then do not do any recording
within an NMI.

Link: https://lore.kernel.org/linux-trace-kernel/20231213175403.6fc18540@gandalf.local.home

Cc: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Mark Rutland <mark.rutland@....com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 kernel/trace/ring_buffer.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index f0d4ff2db2ef0..b1acec3e4dc3b 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -2774,6 +2774,12 @@ rb_reserve_next_event(struct ring_buffer *buffer,
 	int nr_loops = 0;
 	u64 diff;
 
+	/* ring buffer does cmpxchg, make sure it is safe in NMI context */
+	if (!IS_ENABLED(CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG) &&
+	    (unlikely(in_nmi()))) {
+		return NULL;
+	}
+
 	rb_start_commit(cpu_buffer);
 
 #ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
-- 
2.43.0