ring-buffer: Have rb_time_cmpxchg() set the msb counter too

The rb_time_cmpxchg() on 32-bit architectures requires setting three
32-bit words to represent the 64-bit timestamp, with some salt for
synchronization. Those are: msb, top, and bottom

The issue is, the rb_time_cmpxchg() did not properly salt the msb portion,
and the msb that was written was stale.

Link: https://lore.kernel.org/linux-trace-kernel/20231215084114.20899342@rorschach.local.home
Cc: stable@vger.kernel.org
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Fixes: f03f2abce4f39 ("ring-buffer: Have 32 bit time stamps use all 64 bits")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index f22a849da1797a4df3cdddb745796426e9d03a75..f4679013289bad9dcfdd1def9014b9a99581a0cc 100644 (file)
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -722,10 +722,12 @@ static bool rb_time_cmpxchg(rb_time_t *t, u64 expect, u64 set)
         cnt2 = cnt + 1;
 
         rb_time_split(val, &top, &bottom, &msb);
+        msb = rb_time_val_cnt(msb, cnt);
         top = rb_time_val_cnt(top, cnt);
         bottom = rb_time_val_cnt(bottom, cnt);
 
         rb_time_split(set, &top2, &bottom2, &msb2);
+        msb2 = rb_time_val_cnt(msb2, cnt);
         top2 = rb_time_val_cnt(top2, cnt2);
         bottom2 = rb_time_val_cnt(bottom2, cnt2);