ring-buffer: Update write stamp with the correct ts

The write stamp, used to calculate deltas between events, was updated with
the stale "ts" value in the "info" structure, and not with the updated "ts"
variable. This caused the deltas between events to be inaccurate, and when
crossing into a new sub buffer, had time go backwards.

Link: https://lkml.kernel.org/r/[email protected]

Cc: [email protected]
Fixes: a389d86f7f ("ring-buffer: Have nested events still record running time stamp")
Reported-by: "J. Avila" <[email protected]>
Tested-by: Daniel Mentz <[email protected]>
Tested-by: Will McVicker <[email protected]>
Signed-off-by: Steven Rostedt (VMware) <[email protected]>

kernel/trace/ring_buffer.c

@@ -3291,7 +3291,7 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
 			/* Nothing came after this event between C and E */
 			info->delta = ts - info->after;
 			(void)rb_time_cmpxchg(&cpu_buffer->write_stamp,
-					      info->after, info->ts);
+					      info->after, ts);
 			info->ts = ts;
 		} else {
 			/*