ring-buffer: Do not allow events in NMI with generic atomic64 cmpxchg()

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: [email protected]
Cc: Mark Rutland <[email protected]>
Cc: Mathieu Desnoyers <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Andreas Larsson <[email protected]>
Link: https://lore.kernel.org/[email protected]
Fixes: c84897c ("ring-buffer: Remove 32bit timestamp logic")
Closes: https://lore.kernel.org/all/[email protected]/
Reported-by: Ludwig Rydberg <[email protected]>
Reviewed-by: Masami Hiramatsu (Google) <[email protected]>
Signed-off-by: Steven Rostedt (Google) <[email protected]>

Author: rostedt

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;
 	}