linux-kernel - [for-linus][PATCH 14/15] ring-buffer: Have rb_time

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Message-ID: <20231216042245.708750639@goodmis.org>
Date: Fri, 15 Dec 2023 23:22:28 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: linux-kernel@...r.kernel.org
Cc: Masami Hiramatsu <mhiramat@...nel.org>,
 Mark Rutland <mark.rutland@....com>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 stable@...r.kernel.org
Subject: [for-linus][PATCH 14/15] ring-buffer: Have rb_time_cmpxchg() set the msb counter too

From: "Steven Rostedt (Google)" <rostedt@...dmis.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.local.home

Cc: stable@...r.kernel.org
Cc: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Mark Rutland <mark.rutland@....com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Fixes: f03f2abce4f39 ("ring-buffer: Have 32 bit time stamps use all 64 bits")
Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.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);
 
-- 
2.42.0