[PATCH 1/2] ring-buffer: Do not allow events in NMI with generic atomic64 cmpxchg()

[Steven Rostedt <rostedt@goodmis.org>]

From: Steven Rostedt <rostedt@goodmis.org>

Some architectures can not safely do atomic64 operations in NMI context.
Since the ring buffer relies on atomic64 operations to do its time
keeping, if an event is requested in NMI context, reject it for these
architectures.

Cc: stable@vger.kernel.org
Fixes: c84897c0ff592 ("ring-buffer: Remove 32bit timestamp logic")
Closes: https://lore.kernel.org/all/86fb4f86-a0e4-45a2-a2df-3154acc4f086@gaisler.com/
Reported-by: Ludwig Rydberg <ludwig.rydberg@gaisler.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 kernel/trace/ring_buffer.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 6d61ff78926b..b8e0ae15ca5b 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -4398,8 +4398,13 @@ 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) &&
+	/*
+	 * ring buffer does cmpxchg as well as atomic64 operations
+	 * (which some archs use locking for atomic64), make sure this
+	 * is safe in NMI context
+	 */
+	if ((!IS_ENABLED(CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG) ||
+	     IS_ENABLED(CONFIG_GENERIC_ATOMIC64)) &&
 	    (unlikely(in_nmi()))) {
 		return NULL;
 	}
-- 
2.45.2