[PATCH AUTOSEL 5.4 7/7] ring-buffer: Do not record in NMI if the arch does not support cmpxchg in NMI

[Sasha Levin <sashal@kernel.org>]

From: "Steven Rostedt (Google)" <rostedt@goodmis.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@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Sasha Levin <sashal@kernel.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 9d6ba38791961..983fc4475c273 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -2969,6 +2969,12 @@ 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