From: "Steven Rostedt (Google)" rostedt@goodmis.org

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...

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 --- kernel/trace/ring_buffer.c | 2 ++ 1 file changed, 2 insertions(+)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index f22a849da179..f4679013289b 100644 --- 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);