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Date: Mon, 06 Aug 2012 22:40:20 -0700
From: John Stultz <johnstul@...ibm.com>
To: Sasha Levin <levinsasha928@...il.com>
CC: Avi Kivity <avi@...hat.com>, paulmck@...ux.vnet.ibm.com,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
mingo@...nel.org, a.p.zijlstra@...llo.nl, prarit@...hat.com,
tglx@...utronix.de, Dave Jones <davej@...hat.com>
Subject: Re: rcu: INFO: rcu_preempt detected stalls on CPUs/tasks on v3.6
On 08/06/2012 11:28 AM, Sasha Levin wrote:
> On 08/06/2012 08:20 PM, John Stultz wrote:
>> On 08/06/2012 10:21 AM, John Stultz wrote:
>>> On 08/05/2012 09:55 AM, Sasha Levin wrote:
>>>> On 07/30/2012 03:17 PM, Avi Kivity wrote:
>>>>> Possible causes:
>>>>> - the APIC calibration in the guest failed, so it is programming too
>>>>> low values into the timer
>>>>> - it actually needs 1 us wakeups and then can't keep up (esp. as kvm
>>>>> interrupt injection is slowing it down)
>>>>>
>>>>> You can try to find out by changing
>>>>> arch/x86/kvm/lapic.c:start_lapic_timer() to impose a minimum wakeup of
>>>>> (say) 20 microseconds which will let the guest live long enough for you
>>>>> to ftrace it and see what kind of timers it is programming.
>>>> I've kept trying to narrow it down, and found out It's triggerable using adjtimex().
>> Sorry, one more question: Could you provide details on how is it trigger-able using adjtimex?
> It triggers after a while of fuzzing using trinity of just adjtimex ('./trinity --quiet -l off -cadjtimex').
>
> Trinity is available here: http://git.codemonkey.org.uk/?p=trinity.git .
>
> Let me know if I can help further with reproducing this, I can probably copy over my testing environment to some other host if you'd like.
Ok. Finally I *think* got it reproduced. (Had some trouble initially,
as I think since the first time I ran it as a normal user, the socket
cache isn't the same as if you run it the first time as root? Anyway,
after doing a make clean and rebuilding it started to trigger).
I'm not seeing the rcu stall message, but I do manage to trigger two
other behaviors: a hard hang and a sort of zombie state where memory
isn't properly being freed & everything starts segfaulting. So this
may not be the exact same issue, but it triggers quickly as you
described (within a few seconds of running trinity as root).
It looks like both of these issues are caused by
adjtimex(ADJ_SETOFFSET), which adds or subtracts a huge offset and that
either goes negative or gets clamped to a ktime_t at KTIME_MAX (if you
get clamped the system hangs, if it goes negative, the system barely
functions, but sort of drags along).
An updated version of my KTIME_MAX sanity checking patch to handle both
of these conditions is below.
Would you mind giving this patch a shot and letting me know if you still
see problems?
thanks
-john
From 7a37a171f8b93ce8f89137d2dfac37fdc45994ba Mon Sep 17 00:00:00 2001
From: John Stultz <john.stultz@...aro.org>
Date: Tue, 31 Jul 2012 02:06:14 -0400
Subject: [PATCH] time: Improve sanity checking of timekeeping inputs
Unexpected behavior could occur if the time is set to
a value large enough to overflow a 64bit ktime_t
(which is something larger then the year 2262).
Also unexpected behavior could occur if large negative
offsets are injected via adjtimex.
So this patch improves the sanity check timekeeping inputs
by improving the timespec_valid() check, and then makes better
use of timespec_valid() to make sure we don't set the time to
an invalid negative value or one that overflows ktime_t.
Note: This does not protect from setting the time close to
overflowing ktime_t and then letting natural accumulation
cause the overflow.
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Prarit Bhargava <prarit@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Zhouping Liu <zliu@...hat.com>
Cc: CAI Qian <caiqian@...hat.com>
Cc: Sasha Levin <levinsasha928@...il.com>
Cc: stable@...r.kernel.org
Reported-by: CAI Qian <caiqian@...hat.com>
Reported-by: Sasha Levin <levinsasha928@...il.com>
Signed-off-by: John Stultz <john.stultz@...aro.org>
---
include/linux/ktime.h | 7 -------
include/linux/time.h | 23 +++++++++++++++++++++--
kernel/time/timekeeping.c | 26 ++++++++++++++++++++++++--
3 files changed, 45 insertions(+), 11 deletions(-)
diff --git a/include/linux/ktime.h b/include/linux/ktime.h
index 603bec2..06177ba10 100644
--- a/include/linux/ktime.h
+++ b/include/linux/ktime.h
@@ -58,13 +58,6 @@ union ktime {
typedef union ktime ktime_t; /* Kill this */
-#define KTIME_MAX ((s64)~((u64)1 << 63))
-#if (BITS_PER_LONG == 64)
-# define KTIME_SEC_MAX (KTIME_MAX / NSEC_PER_SEC)
-#else
-# define KTIME_SEC_MAX LONG_MAX
-#endif
-
/*
* ktime_t definitions when using the 64-bit scalar representation:
*/
diff --git a/include/linux/time.h b/include/linux/time.h
index c81c5e4..68e68c5 100644
--- a/include/linux/time.h
+++ b/include/linux/time.h
@@ -107,11 +107,30 @@ static inline struct timespec timespec_sub(struct timespec lhs,
return ts_delta;
}
+#define KTIME_MAX ((s64)~((u64)1 << 63))
+#if (BITS_PER_LONG == 64)
+# define KTIME_SEC_MAX (KTIME_MAX / NSEC_PER_SEC)
+#else
+# define KTIME_SEC_MAX LONG_MAX
+#endif
+
/*
* Returns true if the timespec is norm, false if denorm:
*/
-#define timespec_valid(ts) \
- (((ts)->tv_sec >= 0) && (((unsigned long) (ts)->tv_nsec) < NSEC_PER_SEC))
+static inline bool timespec_valid(const struct timespec *ts)
+{
+ /* Dates before 1970 are bogus */
+ if (ts->tv_sec < 0)
+ return false;
+ /* Can't have more nanoseconds then a second */
+ if ((unsigned long)ts->tv_nsec >= NSEC_PER_SEC)
+ return false;
+ /* Disallow values that could overflow ktime_t */
+ if ((unsigned long long)ts->tv_sec >= KTIME_SEC_MAX)
+ return false;
+ return true;
+}
+
extern void read_persistent_clock(struct timespec *ts);
extern void read_boot_clock(struct timespec *ts);
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index e16af19..898bef0 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -427,7 +427,7 @@ int do_settimeofday(const struct timespec *tv)
struct timespec ts_delta, xt;
unsigned long flags;
- if ((unsigned long)tv->tv_nsec >= NSEC_PER_SEC)
+ if (!timespec_valid(tv))
return -EINVAL;
write_seqlock_irqsave(&tk->lock, flags);
@@ -463,6 +463,8 @@ int timekeeping_inject_offset(struct timespec *ts)
{
struct timekeeper *tk = &timekeeper;
unsigned long flags;
+ struct timespec tmp;
+ int ret = 0;
if ((unsigned long)ts->tv_nsec >= NSEC_PER_SEC)
return -EINVAL;
@@ -471,10 +473,17 @@ int timekeeping_inject_offset(struct timespec *ts)
timekeeping_forward_now(tk);
+ /* Make sure the proposed value is valid */
+ tmp = timespec_add(tk_xtime(tk), *ts);
+ if (!timespec_valid(&tmp)) {
+ ret = -EINVAL;
+ goto error;
+ }
tk_xtime_add(tk, ts);
tk_set_wall_to_mono(tk, timespec_sub(tk->wall_to_monotonic, *ts));
+error: /* even if we error out, we forwarded the time, so call update */
timekeeping_update(tk, true);
write_sequnlock_irqrestore(&tk->lock, flags);
@@ -482,7 +491,7 @@ int timekeeping_inject_offset(struct timespec *ts)
/* signal hrtimers about time change */
clock_was_set();
- return 0;
+ return ret;
}
EXPORT_SYMBOL(timekeeping_inject_offset);
@@ -649,7 +658,20 @@ void __init timekeeping_init(void)
struct timespec now, boot, tmp;
read_persistent_clock(&now);
+ if (!timespec_valid(&now)) {
+ pr_warn("WARNING: Persistent clock returned invalid value!\n"
+ " Check your CMOS/BIOS settings.\n");
+ now.tv_sec = 0;
+ now.tv_nsec = 0;
+ }
+
read_boot_clock(&boot);
+ if (!timespec_valid(&boot)) {
+ pr_warn("WARNING: Boot clock returned invalid value!\n"
+ " Check your CMOS/BIOS settings.\n");
+ boot.tv_sec = 0;
+ boot.tv_nsec = 0;
+ }
seqlock_init(&tk->lock);
--
1.7.9.5
--
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