linux-kernel - [PATCH 4.8 028/138] ALSA: seq: Fix time account regression

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Date:   Wed,  9 Nov 2016 11:45:11 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Yves Guillemot <yc.guillemot@...adoo.fr>,
        Takashi Iwai <tiwai@...e.de>
Subject: [PATCH 4.8 028/138] ALSA: seq: Fix time account regression

4.8-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Takashi Iwai <tiwai@...e.de>

commit 9b50898ad96c793a8f7cde9d8f281596d752a7dd upstream.

The recent rewrite of the sequencer time accounting using timespec64
in the commit [3915bf294652: ALSA: seq_timer: use monotonic times
internally] introduced a bad regression.  Namely, the time reported
back doesn't increase but goes back and forth.

The culprit was obvious: the delta is stored to the result (cur_time =
delta), instead of adding the delta (cur_time += delta)!

Let's fix it.

Fixes: 3915bf294652 ('ALSA: seq_timer: use monotonic times internally')
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=177571
Reported-by: Yves Guillemot <yc.guillemot@...adoo.fr>
Signed-off-by: Takashi Iwai <tiwai@...e.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 sound/core/seq/seq_timer.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/sound/core/seq/seq_timer.c
+++ b/sound/core/seq/seq_timer.c
@@ -448,8 +448,8 @@ snd_seq_real_time_t snd_seq_timer_get_cu
 
 		ktime_get_ts64(&tm);
 		tm = timespec64_sub(tm, tmr->last_update);
-		cur_time.tv_nsec = tm.tv_nsec;
-		cur_time.tv_sec = tm.tv_sec;
+		cur_time.tv_nsec += tm.tv_nsec;
+		cur_time.tv_sec += tm.tv_sec;
 		snd_seq_sanity_real_time(&cur_time);
 	}
 	spin_unlock_irqrestore(&tmr->lock, flags);