linux-kernel - [for-linus][PATCH 05/12] ring-buffer: Update write stamp with the correct ts

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Message-ID: <20201201160005.780999537@goodmis.org>
Date:   Tue, 01 Dec 2020 10:58:40 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     linux-kernel@...r.kernel.org
Cc:     Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        stable@...r.kernel.org, "J. Avila" <elavila@...gle.com>,
        Daniel Mentz <danielmentz@...gle.com>,
        Will McVicker <willmcvicker@...gle.com>
Subject: [for-linus][PATCH 05/12] ring-buffer: Update write stamp with the correct ts

From: "Steven Rostedt (VMware)" <rostedt@...dmis.org>

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/20201124223917.795844-1-elavila@google.com

Cc: stable@...r.kernel.org
Fixes: a389d86f7fd09 ("ring-buffer: Have nested events still record running time stamp")
Reported-by: "J. Avila" <elavila@...gle.com>
Tested-by: Daniel Mentz <danielmentz@...gle.com>
Tested-by: Will McVicker <willmcvicker@...gle.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
---
 kernel/trace/ring_buffer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index dc83b3fa9fe7..bccaf88d3706 100644
--- a/kernel/trace/ring_buffer.c
+++ b/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 {
 			/*
-- 
2.28.0