Re: CONFIG_NO_HZ + CONFIG_CPU_IDLE freeze the system (Was Re: [PATCH] acpi : remove power from acpi_processor_cx structure)

John Stultz
Tue, 11 Sep 2012 00:18:58 -0000

On 09/10/2012 12:45 PM, Daniel Lezcano wrote:
> On 09/10/2012 07:14 PM, John Stultz wrote:
>> In the meantime, I''ll try to reproduce on my T61. If you could
send me
>> your .config, I''d appreciate it.
> http://pastebin.com/qSxqfdDK
>
> The header of the config file shows for a v3.5-rc7 because it is the
> result of the git-bisect. If you keep this config file for the latest
> kernel that should reproduce the problem.
>
> Let me know if you were able to reproduce the problem.
Great! With this I was able to quickly reproduce the problem and I think
I have a fix.

Would you mind testing the following patch? It seems to resolve the
issue, but I''ve not yet run it through my test suite to make sure it
didn''t break anything else.

If both your and my testing comes back ok, I''ll submit it to Thomas.

thanks
-john

 From f10a285a5b532a14d3330f6e60e4d7bd5627932a Mon Sep 17 00:00:00 2001
From: John Stultz <john.stultz@linaro.org>
Date: Mon, 10 Sep 2012 20:00:15 -0400
Subject: [PATCH] time: Fix timeekeping_get_ns overflow on 32bit systems

Daniel Lezcano reported seeing multi-second stalls from
keyboard input on his T61 laptop when NOHZ and CPU_IDLE
were enabled on a 32bit kernel.

He bisected the problem down to
1e75fa8be9fb61e1af46b5b3b176347a4c958ca1 (time: Condense
timekeeper.xtime into xtime_sec).

After reproducing this issue, I narrowed the problem down
to the fact that timekeeping_get_ns() returns a 64bit
nsec value that hasn''t been accumulated. In some cases
this value was being then stored in timespec.tv_nsec
(which is a long).

On 32bit systems, With idle times larger then 4 seconds
(or less, depending on the value of xtime_nsec), the
returned nsec value would overflow 32bits. This limited
kept time from increasing, causing timers to not expire.

The fix is to make sure we don''t directly store the
result of timekeeping_get_ns() into a tv_nsec field,
instead using a 64bit nsec value which can then be
added into the timespec via timespec_add_ns().

With this patch I cannot reproduce the issue.

Cc: Ingo Molnar <mingo@kernel.org>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Reported-and-bisected-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: John Stultz <john.stultz@linaro.org>
---
  kernel/time/timekeeping.c |   19 ++++++++++++-------
  1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 34e5eac..d3b91e7 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -303,10 +303,11 @@ void getnstimeofday(struct timespec *ts)
  		seq = read_seqbegin(&tk->lock);

  		ts->tv_sec = tk->xtime_sec;
-		ts->tv_nsec = timekeeping_get_ns(tk);
+		nsecs = timekeeping_get_ns(tk);

  	} while (read_seqretry(&tk->lock, seq));

+	ts->tv_nsec = 0;
  	timespec_add_ns(ts, nsecs);
  }
  EXPORT_SYMBOL(getnstimeofday);
@@ -345,6 +346,7 @@ void ktime_get_ts(struct timespec *ts)
  {
  	struct timekeeper *tk = &timekeeper;
  	struct timespec tomono;
+	s64 nsec;
  	unsigned int seq;

  	WARN_ON(timekeeping_suspended);
@@ -352,13 +354,14 @@ void ktime_get_ts(struct timespec *ts)
  	do {
  		seq = read_seqbegin(&tk->lock);
  		ts->tv_sec = tk->xtime_sec;
-		ts->tv_nsec = timekeeping_get_ns(tk);
+		nsec = timekeeping_get_ns(tk);
  		tomono = tk->wall_to_monotonic;

  	} while (read_seqretry(&tk->lock, seq));

-	set_normalized_timespec(ts, ts->tv_sec + tomono.tv_sec,
-				ts->tv_nsec + tomono.tv_nsec);
+	ts->tv_sec += tomono.tv_sec;
+	ts->tv_nsec = 0;
+	timespec_add_ns(ts, nsec + tomono.tv_nsec);
  }
  EXPORT_SYMBOL_GPL(ktime_get_ts);

@@ -1244,6 +1247,7 @@ void get_monotonic_boottime(struct timespec *ts)
  {
  	struct timekeeper *tk = &timekeeper;
  	struct timespec tomono, sleep;
+	s64 nsec;
  	unsigned int seq;

  	WARN_ON(timekeeping_suspended);
@@ -1251,14 +1255,15 @@ void get_monotonic_boottime(struct timespec *ts)
  	do {
  		seq = read_seqbegin(&tk->lock);
  		ts->tv_sec = tk->xtime_sec;
-		ts->tv_nsec = timekeeping_get_ns(tk);
+		nsec = timekeeping_get_ns(tk);
  		tomono = tk->wall_to_monotonic;
  		sleep = tk->total_sleep_time;

  	} while (read_seqretry(&tk->lock, seq));

-	set_normalized_timespec(ts, ts->tv_sec + tomono.tv_sec + sleep.tv_sec,
-			ts->tv_nsec + tomono.tv_nsec + sleep.tv_nsec);
+	ts->tv_sec += tomono.tv_sec + sleep.tv_sec;
+	ts->tv_nsec = 0;
+	timespec_add_ns(ts, nsec + tomono.tv_nsec + sleep.tv_nsec);
  }
  EXPORT_SYMBOL_GPL(get_monotonic_boottime);

--
1.7.9.5