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Subject[PATCH] ring-buffer: Have rb_time_cmpxchg() set the msb counter too
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.

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 78aacc78f03a..e9c10eabdb95 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);

--
2.42.0

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