tracing/rseq: Add mm_cid field to rseq_update

Add the mm_cid field to the rseq_update event, allowing tracers to
follow which mm_cid is observed by user-space, and whether negative
mm_cid values are visible in case of internal scheduler implementation
issues.
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20221122203932.231377-22-mathieu.desnoyers@efficios.com

include/trace/events/rseq.h

@@ -17,14 +17,17 @@ TRACE_EVENT(rseq_update,
 	TP_STRUCT__entry(
 		__field(s32, cpu_id)
 		__field(s32, node_id)
+		__field(s32, mm_cid)
 	),
 
 	TP_fast_assign(
 		__entry->cpu_id = raw_smp_processor_id();
 		__entry->node_id = cpu_to_node(__entry->cpu_id);
+		__entry->mm_cid = task_mm_cid(t);
 	),
 
-	TP_printk("cpu_id=%d node_id=%d", __entry->cpu_id, __entry->node_id)
+	TP_printk("cpu_id=%d node_id=%d mm_cid=%d", __entry->cpu_id,
+		  __entry->node_id, __entry->mm_cid)
 );
 
 TRACE_EVENT(rseq_ip_fixup,