From: Steven Rostedt (Google) <rostedt@goodmis.org>
Date: Wed, 13 Dec 2023 22:54:03 +0000 (-0500)
Subject: ring-buffer: Do not record in NMI if the arch does not support cmpxchg in NMI
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=712292308af2265cd9b126aedfa987f10f452a33;p=linux.git

ring-buffer: Do not record in NMI if the arch does not support cmpxchg in NMI

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>
---

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index f4679013289ba..5a114e752f110 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -3674,6 +3674,12 @@ rb_reserve_next_event(struct trace_buffer *buffer,
 	int nr_loops = 0;
 	int add_ts_default;
 
+	/* 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);
 	/* The commit page can not change after this */