| Age | Commit message (Collapse) | Author |
|---|
|
switch_hrtimer_base()"
In an rt-kernel with CONFIG_MISSED_TIMER_OFFSETS_HIST enabled,
__hrtimer_start_range_ns() now crashes, as new_base is not assigned
before it is used.
Tested-by: Carsten Emde <C.Emde@osadl.org>
Cc: stable-rt@vger.kernel.org
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
|
|
We hit another bug that was caused by switching cpu_chill() from
msleep() to hrtimer_nanosleep().
This time it is a livelock. The problem is that hrtimer_nanosleep()
calls schedule with the state == TASK_INTERRUPTIBLE. But these means
that if a signal is pending, the scheduler wont schedule, and will
simply change the current task state back to TASK_RUNNING. This
nullifies the whole point of cpu_chill() in the first place. That is,
if a task is spinning on a try_lock() and it preempted the owner of the
lock, if it has a signal pending, it will never give up the CPU to let
the owner of the lock run.
I made a static function __hrtimer_nanosleep() that takes a fifth
parameter "state", which determines the task state of that the
nanosleep() will be in. The normal hrtimer_nanosleep() will act the
same, but cpu_chill() will call the __hrtimer_nanosleep() directly with
the TASK_UNINTERRUPTIBLE state.
cpu_chill() only cares that the first sleep happens, and does not care
about the state of the restart schedule (in hrtimer_nanosleep_restart).
Cc: stable-rt@vger.kernel.org
Reported-by: Ulrich Obergfell <uobergfe@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
|
|
Since we replaced msleep() by hrtimer I see now and then (rarely) this:
| [....] Waiting for /dev to be fully populated...
| =====================================
| [ BUG: udevd/229 still has locks held! ]
| 3.12.11-rt17 #23 Not tainted
| -------------------------------------
| 1 lock held by udevd/229:
| #0: (&type->i_mutex_dir_key#2){+.+.+.}, at: lookup_slow+0x28/0x98
|
| stack backtrace:
| CPU: 0 PID: 229 Comm: udevd Not tainted 3.12.11-rt17 #23
| (unwind_backtrace+0x0/0xf8) from (show_stack+0x10/0x14)
| (show_stack+0x10/0x14) from (dump_stack+0x74/0xbc)
| (dump_stack+0x74/0xbc) from (do_nanosleep+0x120/0x160)
| (do_nanosleep+0x120/0x160) from (hrtimer_nanosleep+0x90/0x110)
| (hrtimer_nanosleep+0x90/0x110) from (cpu_chill+0x30/0x38)
| (cpu_chill+0x30/0x38) from (dentry_kill+0x158/0x1ec)
| (dentry_kill+0x158/0x1ec) from (dput+0x74/0x15c)
| (dput+0x74/0x15c) from (lookup_real+0x4c/0x50)
| (lookup_real+0x4c/0x50) from (__lookup_hash+0x34/0x44)
| (__lookup_hash+0x34/0x44) from (lookup_slow+0x38/0x98)
| (lookup_slow+0x38/0x98) from (path_lookupat+0x208/0x7fc)
| (path_lookupat+0x208/0x7fc) from (filename_lookup+0x20/0x60)
| (filename_lookup+0x20/0x60) from (user_path_at_empty+0x50/0x7c)
| (user_path_at_empty+0x50/0x7c) from (user_path_at+0x14/0x1c)
| (user_path_at+0x14/0x1c) from (vfs_fstatat+0x48/0x94)
| (vfs_fstatat+0x48/0x94) from (SyS_stat64+0x14/0x30)
| (SyS_stat64+0x14/0x30) from (ret_fast_syscall+0x0/0x48)
For now I see no better way but to disable the freezer the sleep the period.
Cc: stable-rt@vger.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
|
|
Ulrich Obergfell pointed out that cpu_chill() calls msleep() which is woken
up by the ksoftirqd running the TIMER softirq. But as the cpu_chill() is
called from softirq context, it may block the ksoftirqd() from running, in
which case, it may never wake up the msleep() causing the deadlock.
I checked the vmcore, and irq/74-qla2xxx is stuck in the msleep() call,
running on CPU 8. The one ksoftirqd that is stuck, happens to be the one that
runs on CPU 8, and it is blocked on a lock held by irq/74-qla2xxx. As that
ksoftirqd is the one that will wake up irq/74-qla2xxx, and it happens to be
blocked on a lock that irq/74-qla2xxx holds, we have our deadlock.
The solution is not to convert the cpu_chill() back to a cpu_relax() as that
will re-create a possible live lock that the cpu_chill() fixed earlier, and may
also leave this bug open on other softirqs. The fix is to remove the
dependency on ksoftirqd from cpu_chill(). That is, instead of calling
msleep() that requires ksoftirqd to wake it up, use the
hrtimer_nanosleep() code that does the wakeup from hard irq context.
|Looks to be the lock of the block softirq. I don't have the core dump
|anymore, but from what I could tell the ksoftirqd was blocked on the
|block softirq lock, where the block softirq handler did a msleep
|(called by the qla2xxx interrupt handler).
|
|Looking at trigger_softirq() in block/blk-softirq.c, it can do a
|smp_callfunction() to another cpu to run the block softirq. If that
|happens to be the cpu where the qla2xx irq handler is doing the block
|softirq and is in a middle of a msleep(), I believe the ksoftirqd will
|try to run the softirq. If it does that, then BOOM, it's deadlocked
|because the ksoftirqd will never run the timer softirq either.
|I should have also stated that it was only one lock that was involved.
|But the lock owner was doing a msleep() that requires a wakeup by
|ksoftirqd to continue. If ksoftirqd happens to be blocked on a lock
|held by the msleep() caller, then you have your deadlock.
|
|It's best not to have any softirqs going to sleep requiring another
|softirq to wake it up. Note, if we ever require a timer softirq to do a
|cpu_chill() it will most definitely hit this deadlock.
Cc: stable-rt@vger.kernel.org
Found-by: Ulrich Obergfell <uobergfe@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
[bigeasy: add the 4 | chapters from email]
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
|
|
Mike,
On Thu, 7 Nov 2013, Mike Galbraith wrote:
> On Thu, 2013-11-07 at 04:26 +0100, Mike Galbraith wrote:
> > On Wed, 2013-11-06 at 18:49 +0100, Thomas Gleixner wrote:
>
> > > I bet you are trying to work around some of the side effects of the
> > > occasional tick which is still necessary despite of full nohz, right?
> >
> > Nope, I wanted to check out cost of nohz_full for rt, and found that it
> > doesn't work at all instead, looked, and found that the sole running
> > task has just awakened ksoftirqd when it wants to shut the tick down, so
> > that shutdown never happens.
>
> Like so in virgin 3.10-rt. Box is x3550 M3 booted nowatchdog
> rcu_nocbs=1-3 nohz_full=1-3, and CPUs1-3 are completely isolated via
> cpusets as well.
well, that very same problem is in mainline if you add "threadirqs" to
the command line. But we can be smart about this. The untested patch
below should address that issue. If that works on mainline we can
adapt it for RT (needs a trylock(&base->lock) there).
Though it's not a full solution. It needs some thought versus the
softirq code of timers. Assume we have only one timer queued 1000
ticks into the future. So this change will cause the timer softirq not
to be called until that timer expires and then the timer softirq is
going to do 1000 loops until it catches up with jiffies. That's
anything but pretty ...
What worries me more is this one:
pert-5229 [003] d..h1.. 684.482618: softirq_raise: vec=9 [action=RCU]
The CPU has no callbacks as you shoved them over to cpu 0, so why is
the RCU softirq raised?
Thanks,
tglx
------------------
Message-id: <alpine.DEB.2.02.1311071158350.23353@ionos.tec.linutronix.de>
|CONFIG_NO_HZ_FULL + CONFIG_PREEMPT_RT_FULL = nogo
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
|
|
When run ltp leapsec_timer test, the following call trace is caught:
BUG: sleeping function called from invalid context at kernel/rtmutex.c:659
in_atomic(): 1, irqs_disabled(): 1, pid: 0, name: swapper/1
Preemption disabled at:[<ffffffff810857f3>] cpu_startup_entry+0x133/0x310
CPU: 1 PID: 0 Comm: swapper/1 Not tainted 3.10.10-rt3 #2
Hardware name: Intel Corporation Calpella platform/MATXM-CORE-411-B, BIOS 4.6.3 08/18/2010
ffffffff81c2f800 ffff880076843e40 ffffffff8169918d ffff880076843e58
ffffffff8106db31 ffff88007684b4a0 ffff880076843e70 ffffffff8169d9c0
ffff88007684b4a0 ffff880076843eb0 ffffffff81059da1 0000001876851200
Call Trace:
<IRQ> [<ffffffff8169918d>] dump_stack+0x19/0x1b
[<ffffffff8106db31>] __might_sleep+0xf1/0x170
[<ffffffff8169d9c0>] rt_spin_lock+0x20/0x50
[<ffffffff81059da1>] queue_work_on+0x61/0x100
[<ffffffff81065aa1>] clock_was_set_delayed+0x21/0x30
[<ffffffff810883be>] do_timer+0x40e/0x660
[<ffffffff8108f487>] tick_do_update_jiffies64+0xf7/0x140
[<ffffffff8108fe42>] tick_check_idle+0x92/0xc0
[<ffffffff81044327>] irq_enter+0x57/0x70
[<ffffffff816a040e>] smp_apic_timer_interrupt+0x3e/0x9b
[<ffffffff8169f80a>] apic_timer_interrupt+0x6a/0x70
<EOI> [<ffffffff8155ea1c>] ? cpuidle_enter_state+0x4c/0xc0
[<ffffffff8155eb68>] cpuidle_idle_call+0xd8/0x2d0
[<ffffffff8100b59e>] arch_cpu_idle+0xe/0x30
[<ffffffff8108585e>] cpu_startup_entry+0x19e/0x310
[<ffffffff8168efa2>] start_secondary+0x1ad/0x1b0
The clock_was_set_delayed is called in hard IRQ handler (timer interrupt), which
calls schedule_work.
Under PREEMPT_RT_FULL, schedule_work calls spinlocks which could sleep, so it's
not safe to call schedule_work in interrupt context.
Reference upstream commit b68d61c705ef02384c0538b8d9374545097899ca
(rt,ntp: Move call to schedule_delayed_work() to helper thread)
from git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-stable-rt.git, which
makes a similar change.
add a helper thread which does the call to schedule_work and wake up that
thread instead of calling schedule_work directly.
Cc: stable-rt@vger.kernel.org
Signed-off-by: Yang Shi <yang.shi@windriver.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
|
|
When the hrtimer stall detection hits the softirq is not raised.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable-rt@vger.kernel.org
|
|
In preempt-rt we can not call the callbacks which take sleeping locks
from the timer interrupt context.
Bring back the softirq split for now, until we fixed the signal
delivery problem for real.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
|
|
Make cancellation of a running callback in softirq context safe
against preemption.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
|
|
This patch provides a recording mechanism to store data of potential
sources of system latencies. The recordings separately determine the
latency caused by a delayed timer expiration, by a delayed wakeup of the
related user space program and by the sum of both. The histograms can be
enabled and reset individually. The data are accessible via the debug
filesystem. For details please consult Documentation/trace/histograms.txt.
Signed-off-by: Carsten Emde <C.Emde@osadl.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
|
|
|
|
We hit another bug that was caused by switching cpu_chill() from
msleep() to hrtimer_nanosleep().
This time it is a livelock. The problem is that hrtimer_nanosleep()
calls schedule with the state == TASK_INTERRUPTIBLE. But these means
that if a signal is pending, the scheduler wont schedule, and will
simply change the current task state back to TASK_RUNNING. This
nullifies the whole point of cpu_chill() in the first place. That is,
if a task is spinning on a try_lock() and it preempted the owner of the
lock, if it has a signal pending, it will never give up the CPU to let
the owner of the lock run.
I made a static function __hrtimer_nanosleep() that takes a fifth
parameter "state", which determines the task state of that the
nanosleep() will be in. The normal hrtimer_nanosleep() will act the
same, but cpu_chill() will call the __hrtimer_nanosleep() directly with
the TASK_UNINTERRUPTIBLE state.
cpu_chill() only cares that the first sleep happens, and does not care
about the state of the restart schedule (in hrtimer_nanosleep_restart).
Cc: stable-rt@vger.kernel.org
Reported-by: Ulrich Obergfell <uobergfe@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
|
|
Since we replaced msleep() by hrtimer I see now and then (rarely) this:
| [....] Waiting for /dev to be fully populated...
| =====================================
| [ BUG: udevd/229 still has locks held! ]
| 3.12.11-rt17 #23 Not tainted
| -------------------------------------
| 1 lock held by udevd/229:
| #0: (&type->i_mutex_dir_key#2){+.+.+.}, at: lookup_slow+0x28/0x98
|
| stack backtrace:
| CPU: 0 PID: 229 Comm: udevd Not tainted 3.12.11-rt17 #23
| (unwind_backtrace+0x0/0xf8) from (show_stack+0x10/0x14)
| (show_stack+0x10/0x14) from (dump_stack+0x74/0xbc)
| (dump_stack+0x74/0xbc) from (do_nanosleep+0x120/0x160)
| (do_nanosleep+0x120/0x160) from (hrtimer_nanosleep+0x90/0x110)
| (hrtimer_nanosleep+0x90/0x110) from (cpu_chill+0x30/0x38)
| (cpu_chill+0x30/0x38) from (dentry_kill+0x158/0x1ec)
| (dentry_kill+0x158/0x1ec) from (dput+0x74/0x15c)
| (dput+0x74/0x15c) from (lookup_real+0x4c/0x50)
| (lookup_real+0x4c/0x50) from (__lookup_hash+0x34/0x44)
| (__lookup_hash+0x34/0x44) from (lookup_slow+0x38/0x98)
| (lookup_slow+0x38/0x98) from (path_lookupat+0x208/0x7fc)
| (path_lookupat+0x208/0x7fc) from (filename_lookup+0x20/0x60)
| (filename_lookup+0x20/0x60) from (user_path_at_empty+0x50/0x7c)
| (user_path_at_empty+0x50/0x7c) from (user_path_at+0x14/0x1c)
| (user_path_at+0x14/0x1c) from (vfs_fstatat+0x48/0x94)
| (vfs_fstatat+0x48/0x94) from (SyS_stat64+0x14/0x30)
| (SyS_stat64+0x14/0x30) from (ret_fast_syscall+0x0/0x48)
For now I see no better way but to disable the freezer the sleep the period.
Cc: stable-rt@vger.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
|
|
Ulrich Obergfell pointed out that cpu_chill() calls msleep() which is woken
up by the ksoftirqd running the TIMER softirq. But as the cpu_chill() is
called from softirq context, it may block the ksoftirqd() from running, in
which case, it may never wake up the msleep() causing the deadlock.
I checked the vmcore, and irq/74-qla2xxx is stuck in the msleep() call,
running on CPU 8. The one ksoftirqd that is stuck, happens to be the one that
runs on CPU 8, and it is blocked on a lock held by irq/74-qla2xxx. As that
ksoftirqd is the one that will wake up irq/74-qla2xxx, and it happens to be
blocked on a lock that irq/74-qla2xxx holds, we have our deadlock.
The solution is not to convert the cpu_chill() back to a cpu_relax() as that
will re-create a possible live lock that the cpu_chill() fixed earlier, and may
also leave this bug open on other softirqs. The fix is to remove the
dependency on ksoftirqd from cpu_chill(). That is, instead of calling
msleep() that requires ksoftirqd to wake it up, use the
hrtimer_nanosleep() code that does the wakeup from hard irq context.
|Looks to be the lock of the block softirq. I don't have the core dump
|anymore, but from what I could tell the ksoftirqd was blocked on the
|block softirq lock, where the block softirq handler did a msleep
|(called by the qla2xxx interrupt handler).
|
|Looking at trigger_softirq() in block/blk-softirq.c, it can do a
|smp_callfunction() to another cpu to run the block softirq. If that
|happens to be the cpu where the qla2xx irq handler is doing the block
|softirq and is in a middle of a msleep(), I believe the ksoftirqd will
|try to run the softirq. If it does that, then BOOM, it's deadlocked
|because the ksoftirqd will never run the timer softirq either.
|I should have also stated that it was only one lock that was involved.
|But the lock owner was doing a msleep() that requires a wakeup by
|ksoftirqd to continue. If ksoftirqd happens to be blocked on a lock
|held by the msleep() caller, then you have your deadlock.
|
|It's best not to have any softirqs going to sleep requiring another
|softirq to wake it up. Note, if we ever require a timer softirq to do a
|cpu_chill() it will most definitely hit this deadlock.
Cc: stable-rt@vger.kernel.org
Found-by: Ulrich Obergfell <uobergfe@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
[bigeasy: add the 4 | chapters from email]
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
|
|
Mike,
On Thu, 7 Nov 2013, Mike Galbraith wrote:
> On Thu, 2013-11-07 at 04:26 +0100, Mike Galbraith wrote:
> > On Wed, 2013-11-06 at 18:49 +0100, Thomas Gleixner wrote:
>
> > > I bet you are trying to work around some of the side effects of the
> > > occasional tick which is still necessary despite of full nohz, right?
> >
> > Nope, I wanted to check out cost of nohz_full for rt, and found that it
> > doesn't work at all instead, looked, and found that the sole running
> > task has just awakened ksoftirqd when it wants to shut the tick down, so
> > that shutdown never happens.
>
> Like so in virgin 3.10-rt. Box is x3550 M3 booted nowatchdog
> rcu_nocbs=1-3 nohz_full=1-3, and CPUs1-3 are completely isolated via
> cpusets as well.
well, that very same problem is in mainline if you add "threadirqs" to
the command line. But we can be smart about this. The untested patch
below should address that issue. If that works on mainline we can
adapt it for RT (needs a trylock(&base->lock) there).
Though it's not a full solution. It needs some thought versus the
softirq code of timers. Assume we have only one timer queued 1000
ticks into the future. So this change will cause the timer softirq not
to be called until that timer expires and then the timer softirq is
going to do 1000 loops until it catches up with jiffies. That's
anything but pretty ...
What worries me more is this one:
pert-5229 [003] d..h1.. 684.482618: softirq_raise: vec=9 [action=RCU]
The CPU has no callbacks as you shoved them over to cpu 0, so why is
the RCU softirq raised?
Thanks,
tglx
------------------
Message-id: <alpine.DEB.2.02.1311071158350.23353@ionos.tec.linutronix.de>
|CONFIG_NO_HZ_FULL + CONFIG_PREEMPT_RT_FULL = nogo
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
|
|
When run ltp leapsec_timer test, the following call trace is caught:
BUG: sleeping function called from invalid context at kernel/rtmutex.c:659
in_atomic(): 1, irqs_disabled(): 1, pid: 0, name: swapper/1
Preemption disabled at:[<ffffffff810857f3>] cpu_startup_entry+0x133/0x310
CPU: 1 PID: 0 Comm: swapper/1 Not tainted 3.10.10-rt3 #2
Hardware name: Intel Corporation Calpella platform/MATXM-CORE-411-B, BIOS 4.6.3 08/18/2010
ffffffff81c2f800 ffff880076843e40 ffffffff8169918d ffff880076843e58
ffffffff8106db31 ffff88007684b4a0 ffff880076843e70 ffffffff8169d9c0
ffff88007684b4a0 ffff880076843eb0 ffffffff81059da1 0000001876851200
Call Trace:
<IRQ> [<ffffffff8169918d>] dump_stack+0x19/0x1b
[<ffffffff8106db31>] __might_sleep+0xf1/0x170
[<ffffffff8169d9c0>] rt_spin_lock+0x20/0x50
[<ffffffff81059da1>] queue_work_on+0x61/0x100
[<ffffffff81065aa1>] clock_was_set_delayed+0x21/0x30
[<ffffffff810883be>] do_timer+0x40e/0x660
[<ffffffff8108f487>] tick_do_update_jiffies64+0xf7/0x140
[<ffffffff8108fe42>] tick_check_idle+0x92/0xc0
[<ffffffff81044327>] irq_enter+0x57/0x70
[<ffffffff816a040e>] smp_apic_timer_interrupt+0x3e/0x9b
[<ffffffff8169f80a>] apic_timer_interrupt+0x6a/0x70
<EOI> [<ffffffff8155ea1c>] ? cpuidle_enter_state+0x4c/0xc0
[<ffffffff8155eb68>] cpuidle_idle_call+0xd8/0x2d0
[<ffffffff8100b59e>] arch_cpu_idle+0xe/0x30
[<ffffffff8108585e>] cpu_startup_entry+0x19e/0x310
[<ffffffff8168efa2>] start_secondary+0x1ad/0x1b0
The clock_was_set_delayed is called in hard IRQ handler (timer interrupt), which
calls schedule_work.
Under PREEMPT_RT_FULL, schedule_work calls spinlocks which could sleep, so it's
not safe to call schedule_work in interrupt context.
Reference upstream commit b68d61c705ef02384c0538b8d9374545097899ca
(rt,ntp: Move call to schedule_delayed_work() to helper thread)
from git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-stable-rt.git, which
makes a similar change.
add a helper thread which does the call to schedule_work and wake up that
thread instead of calling schedule_work directly.
Cc: stable-rt@vger.kernel.org
Signed-off-by: Yang Shi <yang.shi@windriver.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
|
|
When the hrtimer stall detection hits the softirq is not raised.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable-rt@vger.kernel.org
|
|
In preempt-rt we can not call the callbacks which take sleeping locks
from the timer interrupt context.
Bring back the softirq split for now, until we fixed the signal
delivery problem for real.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
|
|
Make cancellation of a running callback in softirq context safe
against preemption.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
|
|
This patch provides a recording mechanism to store data of potential
sources of system latencies. The recordings separately determine the
latency caused by a delayed timer expiration, by a delayed wakeup of the
related user space program and by the sum of both. The histograms can be
enabled and reset individually. The data are accessible via the debug
filesystem. For details please consult Documentation/trace/histograms.txt.
Signed-off-by: Carsten Emde <C.Emde@osadl.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
|
|
|
|
We hit another bug that was caused by switching cpu_chill() from
msleep() to hrtimer_nanosleep().
This time it is a livelock. The problem is that hrtimer_nanosleep()
calls schedule with the state == TASK_INTERRUPTIBLE. But these means
that if a signal is pending, the scheduler wont schedule, and will
simply change the current task state back to TASK_RUNNING. This
nullifies the whole point of cpu_chill() in the first place. That is,
if a task is spinning on a try_lock() and it preempted the owner of the
lock, if it has a signal pending, it will never give up the CPU to let
the owner of the lock run.
I made a static function __hrtimer_nanosleep() that takes a fifth
parameter "state", which determines the task state of that the
nanosleep() will be in. The normal hrtimer_nanosleep() will act the
same, but cpu_chill() will call the __hrtimer_nanosleep() directly with
the TASK_UNINTERRUPTIBLE state.
cpu_chill() only cares that the first sleep happens, and does not care
about the state of the restart schedule (in hrtimer_nanosleep_restart).
Cc: stable-rt@vger.kernel.org
Reported-by: Ulrich Obergfell <uobergfe@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
|
|
Since we replaced msleep() by hrtimer I see now and then (rarely) this:
| [....] Waiting for /dev to be fully populated...
| =====================================
| [ BUG: udevd/229 still has locks held! ]
| 3.12.11-rt17 #23 Not tainted
| -------------------------------------
| 1 lock held by udevd/229:
| #0: (&type->i_mutex_dir_key#2){+.+.+.}, at: lookup_slow+0x28/0x98
|
| stack backtrace:
| CPU: 0 PID: 229 Comm: udevd Not tainted 3.12.11-rt17 #23
| (unwind_backtrace+0x0/0xf8) from (show_stack+0x10/0x14)
| (show_stack+0x10/0x14) from (dump_stack+0x74/0xbc)
| (dump_stack+0x74/0xbc) from (do_nanosleep+0x120/0x160)
| (do_nanosleep+0x120/0x160) from (hrtimer_nanosleep+0x90/0x110)
| (hrtimer_nanosleep+0x90/0x110) from (cpu_chill+0x30/0x38)
| (cpu_chill+0x30/0x38) from (dentry_kill+0x158/0x1ec)
| (dentry_kill+0x158/0x1ec) from (dput+0x74/0x15c)
| (dput+0x74/0x15c) from (lookup_real+0x4c/0x50)
| (lookup_real+0x4c/0x50) from (__lookup_hash+0x34/0x44)
| (__lookup_hash+0x34/0x44) from (lookup_slow+0x38/0x98)
| (lookup_slow+0x38/0x98) from (path_lookupat+0x208/0x7fc)
| (path_lookupat+0x208/0x7fc) from (filename_lookup+0x20/0x60)
| (filename_lookup+0x20/0x60) from (user_path_at_empty+0x50/0x7c)
| (user_path_at_empty+0x50/0x7c) from (user_path_at+0x14/0x1c)
| (user_path_at+0x14/0x1c) from (vfs_fstatat+0x48/0x94)
| (vfs_fstatat+0x48/0x94) from (SyS_stat64+0x14/0x30)
| (SyS_stat64+0x14/0x30) from (ret_fast_syscall+0x0/0x48)
For now I see no better way but to disable the freezer the sleep the period.
Cc: stable-rt@vger.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
|
|
Ulrich Obergfell pointed out that cpu_chill() calls msleep() which is woken
up by the ksoftirqd running the TIMER softirq. But as the cpu_chill() is
called from softirq context, it may block the ksoftirqd() from running, in
which case, it may never wake up the msleep() causing the deadlock.
I checked the vmcore, and irq/74-qla2xxx is stuck in the msleep() call,
running on CPU 8. The one ksoftirqd that is stuck, happens to be the one that
runs on CPU 8, and it is blocked on a lock held by irq/74-qla2xxx. As that
ksoftirqd is the one that will wake up irq/74-qla2xxx, and it happens to be
blocked on a lock that irq/74-qla2xxx holds, we have our deadlock.
The solution is not to convert the cpu_chill() back to a cpu_relax() as that
will re-create a possible live lock that the cpu_chill() fixed earlier, and may
also leave this bug open on other softirqs. The fix is to remove the
dependency on ksoftirqd from cpu_chill(). That is, instead of calling
msleep() that requires ksoftirqd to wake it up, use the
hrtimer_nanosleep() code that does the wakeup from hard irq context.
|Looks to be the lock of the block softirq. I don't have the core dump
|anymore, but from what I could tell the ksoftirqd was blocked on the
|block softirq lock, where the block softirq handler did a msleep
|(called by the qla2xxx interrupt handler).
|
|Looking at trigger_softirq() in block/blk-softirq.c, it can do a
|smp_callfunction() to another cpu to run the block softirq. If that
|happens to be the cpu where the qla2xx irq handler is doing the block
|softirq and is in a middle of a msleep(), I believe the ksoftirqd will
|try to run the softirq. If it does that, then BOOM, it's deadlocked
|because the ksoftirqd will never run the timer softirq either.
|I should have also stated that it was only one lock that was involved.
|But the lock owner was doing a msleep() that requires a wakeup by
|ksoftirqd to continue. If ksoftirqd happens to be blocked on a lock
|held by the msleep() caller, then you have your deadlock.
|
|It's best not to have any softirqs going to sleep requiring another
|softirq to wake it up. Note, if we ever require a timer softirq to do a
|cpu_chill() it will most definitely hit this deadlock.
Cc: stable-rt@vger.kernel.org
Found-by: Ulrich Obergfell <uobergfe@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
[bigeasy: add the 4 | chapters from email]
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
|
|
Mike,
On Thu, 7 Nov 2013, Mike Galbraith wrote:
> On Thu, 2013-11-07 at 04:26 +0100, Mike Galbraith wrote:
> > On Wed, 2013-11-06 at 18:49 +0100, Thomas Gleixner wrote:
>
> > > I bet you are trying to work around some of the side effects of the
> > > occasional tick which is still necessary despite of full nohz, right?
> >
> > Nope, I wanted to check out cost of nohz_full for rt, and found that it
> > doesn't work at all instead, looked, and found that the sole running
> > task has just awakened ksoftirqd when it wants to shut the tick down, so
> > that shutdown never happens.
>
> Like so in virgin 3.10-rt. Box is x3550 M3 booted nowatchdog
> rcu_nocbs=1-3 nohz_full=1-3, and CPUs1-3 are completely isolated via
> cpusets as well.
well, that very same problem is in mainline if you add "threadirqs" to
the command line. But we can be smart about this. The untested patch
below should address that issue. If that works on mainline we can
adapt it for RT (needs a trylock(&base->lock) there).
Though it's not a full solution. It needs some thought versus the
softirq code of timers. Assume we have only one timer queued 1000
ticks into the future. So this change will cause the timer softirq not
to be called until that timer expires and then the timer softirq is
going to do 1000 loops until it catches up with jiffies. That's
anything but pretty ...
What worries me more is this one:
pert-5229 [003] d..h1.. 684.482618: softirq_raise: vec=9 [action=RCU]
The CPU has no callbacks as you shoved them over to cpu 0, so why is
the RCU softirq raised?
Thanks,
tglx
------------------
Message-id: <alpine.DEB.2.02.1311071158350.23353@ionos.tec.linutronix.de>
|CONFIG_NO_HZ_FULL + CONFIG_PREEMPT_RT_FULL = nogo
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
|
|
When run ltp leapsec_timer test, the following call trace is caught:
BUG: sleeping function called from invalid context at kernel/rtmutex.c:659
in_atomic(): 1, irqs_disabled(): 1, pid: 0, name: swapper/1
Preemption disabled at:[<ffffffff810857f3>] cpu_startup_entry+0x133/0x310
CPU: 1 PID: 0 Comm: swapper/1 Not tainted 3.10.10-rt3 #2
Hardware name: Intel Corporation Calpella platform/MATXM-CORE-411-B, BIOS 4.6.3 08/18/2010
ffffffff81c2f800 ffff880076843e40 ffffffff8169918d ffff880076843e58
ffffffff8106db31 ffff88007684b4a0 ffff880076843e70 ffffffff8169d9c0
ffff88007684b4a0 ffff880076843eb0 ffffffff81059da1 0000001876851200
Call Trace:
<IRQ> [<ffffffff8169918d>] dump_stack+0x19/0x1b
[<ffffffff8106db31>] __might_sleep+0xf1/0x170
[<ffffffff8169d9c0>] rt_spin_lock+0x20/0x50
[<ffffffff81059da1>] queue_work_on+0x61/0x100
[<ffffffff81065aa1>] clock_was_set_delayed+0x21/0x30
[<ffffffff810883be>] do_timer+0x40e/0x660
[<ffffffff8108f487>] tick_do_update_jiffies64+0xf7/0x140
[<ffffffff8108fe42>] tick_check_idle+0x92/0xc0
[<ffffffff81044327>] irq_enter+0x57/0x70
[<ffffffff816a040e>] smp_apic_timer_interrupt+0x3e/0x9b
[<ffffffff8169f80a>] apic_timer_interrupt+0x6a/0x70
<EOI> [<ffffffff8155ea1c>] ? cpuidle_enter_state+0x4c/0xc0
[<ffffffff8155eb68>] cpuidle_idle_call+0xd8/0x2d0
[<ffffffff8100b59e>] arch_cpu_idle+0xe/0x30
[<ffffffff8108585e>] cpu_startup_entry+0x19e/0x310
[<ffffffff8168efa2>] start_secondary+0x1ad/0x1b0
The clock_was_set_delayed is called in hard IRQ handler (timer interrupt), which
calls schedule_work.
Under PREEMPT_RT_FULL, schedule_work calls spinlocks which could sleep, so it's
not safe to call schedule_work in interrupt context.
Reference upstream commit b68d61c705ef02384c0538b8d9374545097899ca
(rt,ntp: Move call to schedule_delayed_work() to helper thread)
from git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-stable-rt.git, which
makes a similar change.
add a helper thread which does the call to schedule_work and wake up that
thread instead of calling schedule_work directly.
Cc: stable-rt@vger.kernel.org
Signed-off-by: Yang Shi <yang.shi@windriver.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
|
|
When the hrtimer stall detection hits the softirq is not raised.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable-rt@vger.kernel.org
|
|
In preempt-rt we can not call the callbacks which take sleeping locks
from the timer interrupt context.
Bring back the softirq split for now, until we fixed the signal
delivery problem for real.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
|
|
Make cancellation of a running callback in softirq context safe
against preemption.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
|
|
This patch provides a recording mechanism to store data of potential
sources of system latencies. The recordings separately determine the
latency caused by a delayed timer expiration, by a delayed wakeup of the
related user space program and by the sum of both. The histograms can be
enabled and reset individually. The data are accessible via the debug
filesystem. For details please consult Documentation/trace/histograms.txt.
Signed-off-by: Carsten Emde <C.Emde@osadl.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
|
|
The __cpuinit type of throwaway sections might have made sense
some time ago when RAM was more constrained, but now the savings
do not offset the cost and complications. For example, the fix in
commit 5e427ec2d0 ("x86: Fix bit corruption at CPU resume time")
is a good example of the nasty type of bugs that can be created
with improper use of the various __init prefixes.
After a discussion on LKML[1] it was decided that cpuinit should go
the way of devinit and be phased out. Once all the users are gone,
we can then finally remove the macros themselves from linux/init.h.
This removes all the uses of the __cpuinit macros from C files in
the core kernel directories (kernel, init, lib, mm, and include)
that don't really have a specific maintainer.
[1] https://lkml.org/lkml/2013/5/20/589
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
|
|
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull timer core updates from Thomas Gleixner:
"The timer changes contain:
- posix timer code consolidation and fixes for odd corner cases
- sched_clock implementation moved from ARM to core code to avoid
duplication by other architectures
- alarm timer updates
- clocksource and clockevents unregistration facilities
- clocksource/events support for new hardware
- precise nanoseconds RTC readout (Xen feature)
- generic support for Xen suspend/resume oddities
- the usual lot of fixes and cleanups all over the place
The parts which touch other areas (ARM/XEN) have been coordinated with
the relevant maintainers. Though this results in an handful of
trivial to solve merge conflicts, which we preferred over nasty cross
tree merge dependencies.
The patches which have been committed in the last few days are bug
fixes plus the posix timer lot. The latter was in akpms queue and
next for quite some time; they just got forgotten and Frederic
collected them last minute."
* 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (59 commits)
hrtimer: Remove unused variable
hrtimers: Move SMP function call to thread context
clocksource: Reselect clocksource when watchdog validated high-res capability
posix-cpu-timers: don't account cpu timer after stopped thread runtime accounting
posix_timers: fix racy timer delta caching on task exit
posix-timers: correctly get dying task time sample in posix_cpu_timer_schedule()
selftests: add basic posix timers selftests
posix_cpu_timers: consolidate expired timers check
posix_cpu_timers: consolidate timer list cleanups
posix_cpu_timer: consolidate expiry time type
tick: Sanitize broadcast control logic
tick: Prevent uncontrolled switch to oneshot mode
tick: Make oneshot broadcast robust vs. CPU offlining
x86: xen: Sync the CMOS RTC as well as the Xen wallclock
x86: xen: Sync the wallclock when the system time is set
timekeeping: Indicate that clock was set in the pvclock gtod notifier
timekeeping: Pass flags instead of multiple bools to timekeeping_update()
xen: Remove clock_was_set() call in the resume path
hrtimers: Support resuming with two or more CPUs online (but stopped)
timer: Fix jiffies wrap behavior of round_jiffies_common()
...
|
|
Sigh, should have noticed myself.
Reported-by: fengguang.wu@intel.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
|
|
smp_call_function_* must not be called from softirq context.
But clock_was_set() which calls on_each_cpu() is called from softirq
context to implement a delayed clock_was_set() for the timer interrupt
handler. Though that almost never gets invoked. A recent change in the
resume code uses the softirq based delayed clock_was_set to support
Xens resume mechanism.
linux-next contains a new warning which warns if smp_call_function_*
is called from softirq context which gets triggered by that Xen
change.
Fix this by moving the delayed clock_was_set() call to a work context.
Reported-and-tested-by: Artem Savkov <artem.savkov@gmail.com>
Reported-by: Sasha Levin <sasha.levin@oracle.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: H. Peter Anvin <hpa@zytor.com>,
Cc: Konrad Wilk <konrad.wilk@oracle.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: xen-devel@lists.xen.org
Cc: stable@vger.kernel.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
|
|
hrtimers_resume() only reprograms the timers for the current CPU as it
assumes that all other CPUs are offline at this point in the resume
process. If other CPUs are online then their timers will not be
corrected and they may fire at the wrong time.
When running as a Xen guest, this assumption is not true. Non-boot
CPUs are only stopped with IRQs disabled instead of offlining them.
This is a performance optimization as disabling the CPUs would add an
unacceptable amount of additional downtime during a live migration (>
200 ms for a 4 VCPU guest).
hrtimers_resume() cannot call on_each_cpu(retrigger_next_event,...)
as the other CPUs will be stopped with IRQs disabled. Instead, defer
the call to the next softirq.
[ tglx: Separated the xen change out ]
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: <xen-devel@lists.xen.org>
Link: http://lkml.kernel.org/r/1372329348-20841-2-git-send-email-david.vrabel@citrix.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
|
|
Avoid waking up every thread sleeping in a nanosleep call during
suspend and resume by calling a freezable blocking call. Previous
patches modified the freezer to avoid sending wakeups to threads
that are blocked in freezable blocking calls.
This call was selected to be converted to a freezable call because
it doesn't hold any locks or release any resources when interrupted
that might be needed by another freezing task or a kernel driver
during suspend, and is a common site where idle userspace tasks are
blocked.
Acked-by: Tejun Heo <tj@kernel.org>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Colin Cross <ccross@android.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
|
|
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull 'full dynticks' support from Ingo Molnar:
"This tree from Frederic Weisbecker adds a new, (exciting! :-) core
kernel feature to the timer and scheduler subsystems: 'full dynticks',
or CONFIG_NO_HZ_FULL=y.
This feature extends the nohz variable-size timer tick feature from
idle to busy CPUs (running at most one task) as well, potentially
reducing the number of timer interrupts significantly.
This feature got motivated by real-time folks and the -rt tree, but
the general utility and motivation of full-dynticks runs wider than
that:
- HPC workloads get faster: CPUs running a single task should be able
to utilize a maximum amount of CPU power. A periodic timer tick at
HZ=1000 can cause a constant overhead of up to 1.0%. This feature
removes that overhead - and speeds up the system by 0.5%-1.0% on
typical distro configs even on modern systems.
- Real-time workload latency reduction: CPUs running critical tasks
should experience as little jitter as possible. The last remaining
source of kernel-related jitter was the periodic timer tick.
- A single task executing on a CPU is a pretty common situation,
especially with an increasing number of cores/CPUs, so this feature
helps desktop and mobile workloads as well.
The cost of the feature is mainly related to increased timer
reprogramming overhead when a CPU switches its tick period, and thus
slightly longer to-idle and from-idle latency.
Configuration-wise a third mode of operation is added to the existing
two NOHZ kconfig modes:
- CONFIG_HZ_PERIODIC: [formerly !CONFIG_NO_HZ], now explicitly named
as a config option. This is the traditional Linux periodic tick
design: there's a HZ tick going on all the time, regardless of
whether a CPU is idle or not.
- CONFIG_NO_HZ_IDLE: [formerly CONFIG_NO_HZ=y], this turns off the
periodic tick when a CPU enters idle mode.
- CONFIG_NO_HZ_FULL: this new mode, in addition to turning off the
tick when a CPU is idle, also slows the tick down to 1 Hz (one
timer interrupt per second) when only a single task is running on a
CPU.
The .config behavior is compatible: existing !CONFIG_NO_HZ and
CONFIG_NO_HZ=y settings get translated to the new values, without the
user having to configure anything. CONFIG_NO_HZ_FULL is turned off by
default.
This feature is based on a lot of infrastructure work that has been
steadily going upstream in the last 2-3 cycles: related RCU support
and non-periodic cputime support in particular is upstream already.
This tree adds the final pieces and activates the feature. The pull
request is marked RFC because:
- it's marked 64-bit only at the moment - the 32-bit support patch is
small but did not get ready in time.
- it has a number of fresh commits that came in after the merge
window. The overwhelming majority of commits are from before the
merge window, but still some aspects of the tree are fresh and so I
marked it RFC.
- it's a pretty wide-reaching feature with lots of effects - and
while the components have been in testing for some time, the full
combination is still not very widely used. That it's default-off
should reduce its regression abilities and obviously there are no
known regressions with CONFIG_NO_HZ_FULL=y enabled either.
- the feature is not completely idempotent: there is no 100%
equivalent replacement for a periodic scheduler/timer tick. In
particular there's ongoing work to map out and reduce its effects
on scheduler load-balancing and statistics. This should not impact
correctness though, there are no known regressions related to this
feature at this point.
- it's a pretty ambitious feature that with time will likely be
enabled by most Linux distros, and we'd like you to make input on
its design/implementation, if you dislike some aspect we missed.
Without flaming us to crisp! :-)
Future plans:
- there's ongoing work to reduce 1Hz to 0Hz, to essentially shut off
the periodic tick altogether when there's a single busy task on a
CPU. We'd first like 1 Hz to be exposed more widely before we go
for the 0 Hz target though.
- once we reach 0 Hz we can remove the periodic tick assumption from
nr_running>=2 as well, by essentially interrupting busy tasks only
as frequently as the sched_latency constraints require us to do -
once every 4-40 msecs, depending on nr_running.
I am personally leaning towards biting the bullet and doing this in
v3.10, like the -rt tree this effort has been going on for too long -
but the final word is up to you as usual.
More technical details can be found in Documentation/timers/NO_HZ.txt"
* 'timers-nohz-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (39 commits)
sched: Keep at least 1 tick per second for active dynticks tasks
rcu: Fix full dynticks' dependency on wide RCU nocb mode
nohz: Protect smp_processor_id() in tick_nohz_task_switch()
nohz_full: Add documentation.
cputime_nsecs: use math64.h for nsec resolution conversion helpers
nohz: Select VIRT_CPU_ACCOUNTING_GEN from full dynticks config
nohz: Reduce overhead under high-freq idling patterns
nohz: Remove full dynticks' superfluous dependency on RCU tree
nohz: Fix unavailable tick_stop tracepoint in dynticks idle
nohz: Add basic tracing
nohz: Select wide RCU nocb for full dynticks
nohz: Disable the tick when irq resume in full dynticks CPU
nohz: Re-evaluate the tick for the new task after a context switch
nohz: Prepare to stop the tick on irq exit
nohz: Implement full dynticks kick
nohz: Re-evaluate the tick from the scheduler IPI
sched: New helper to prevent from stopping the tick in full dynticks
sched: Kick full dynticks CPU that have more than one task enqueued.
perf: New helper to prevent full dynticks CPUs from stopping tick
perf: Kick full dynticks CPU if events rotation is needed
...
|
|
The full dynticks tree needs the latest RCU and sched
upstream updates in order to fix some dependencies.
Merge a common upstream merge point that has these
updates.
Conflicts:
include/linux/perf_event.h
kernel/rcutree.h
kernel/rcutree_plugin.h
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
|
|
Reason: Get upstream fixes before adding conflicting code.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
|
|
One can trigger an overflow when using ktime_add_ns() on a 32bit
architecture not supporting CONFIG_KTIME_SCALAR.
When passing a very high value for u64 nsec, e.g. 7881299347898368000
the do_div() function converts this value to seconds (7881299347) which
is still to high to pass to the ktime_set() function as long. The result
in is a negative value.
The problem on my system occurs in the tick-sched.c,
tick_nohz_stop_sched_tick() when time_delta is set to
timekeeping_max_deferment(). The check for time_delta < KTIME_MAX is
valid, thus ktime_add_ns() is called with a too large value resulting in
a negative expire value. This leads to an endless loop in the ticker code:
time_delta: 7881299347898368000
expires = ktime_add_ns(last_update, time_delta)
expires: negative value
This fix caps the value to KTIME_MAX.
This error doesn't occurs on 64bit or architectures supporting
CONFIG_KTIME_SCALAR (e.g. ARM, x86-32).
Cc: stable@vger.kernel.org
Signed-off-by: David Engraf <david.engraf@sysgo.com>
[jstultz: Minor tweaks to commit message & header]
Signed-off-by: John Stultz <john.stultz@linaro.org>
|
|
The settimeofday01 test in the LTP testsuite effectively does
gettimeofday(current time);
settimeofday(Jan 1, 1970 + 100 seconds);
settimeofday(current time);
This test causes a stack trace to be displayed on the console during the
setting of timeofday to Jan 1, 1970 + 100 seconds:
[ 131.066751] ------------[ cut here ]------------
[ 131.096448] WARNING: at kernel/time/clockevents.c:209 clockevents_program_event+0x135/0x140()
[ 131.104935] Hardware name: Dinar
[ 131.108150] Modules linked in: sg nfsv3 nfs_acl nfsv4 auth_rpcgss nfs dns_resolver fscache lockd sunrpc nf_conntrack_netbios_ns nf_conntrack_broadcast ipt_MASQUERADE ip6table_mangle ip6t_REJECT nf_conntrack_ipv6 nf_defrag_ipv6 iptable_nat nf_nat_ipv4 nf_nat iptable_mangle ipt_REJECT nf_conntrack_ipv4 nf_defrag_ipv4 xt_conntrack nf_conntrack ebtable_filter ebtables ip6table_filter ip6_tables iptable_filter ip_tables kvm_amd kvm sp5100_tco bnx2 i2c_piix4 crc32c_intel k10temp fam15h_power ghash_clmulni_intel amd64_edac_mod pcspkr serio_raw edac_mce_amd edac_core microcode xfs libcrc32c sr_mod sd_mod cdrom ata_generic crc_t10dif pata_acpi radeon i2c_algo_bit drm_kms_helper ttm drm ahci pata_atiixp libahci libata usb_storage i2c_core dm_mirror dm_region_hash dm_log dm_mod
[ 131.176784] Pid: 0, comm: swapper/28 Not tainted 3.8.0+ #6
[ 131.182248] Call Trace:
[ 131.184684] <IRQ> [<ffffffff810612af>] warn_slowpath_common+0x7f/0xc0
[ 131.191312] [<ffffffff8106130a>] warn_slowpath_null+0x1a/0x20
[ 131.197131] [<ffffffff810b9fd5>] clockevents_program_event+0x135/0x140
[ 131.203721] [<ffffffff810bb584>] tick_program_event+0x24/0x30
[ 131.209534] [<ffffffff81089ab1>] hrtimer_interrupt+0x131/0x230
[ 131.215437] [<ffffffff814b9600>] ? cpufreq_p4_target+0x130/0x130
[ 131.221509] [<ffffffff81619119>] smp_apic_timer_interrupt+0x69/0x99
[ 131.227839] [<ffffffff8161805d>] apic_timer_interrupt+0x6d/0x80
[ 131.233816] <EOI> [<ffffffff81099745>] ? sched_clock_cpu+0xc5/0x120
[ 131.240267] [<ffffffff814b9ff0>] ? cpuidle_wrap_enter+0x50/0xa0
[ 131.246252] [<ffffffff814b9fe9>] ? cpuidle_wrap_enter+0x49/0xa0
[ 131.252238] [<ffffffff814ba050>] cpuidle_enter_tk+0x10/0x20
[ 131.257877] [<ffffffff814b9c89>] cpuidle_idle_call+0xa9/0x260
[ 131.263692] [<ffffffff8101c42f>] cpu_idle+0xaf/0x120
[ 131.268727] [<ffffffff815f8971>] start_secondary+0x255/0x257
[ 131.274449] ---[ end trace 1151a50552231615 ]---
When we change the system time to a low value like this, the value of
timekeeper->offs_real will be a negative value.
It seems that the WARN occurs because an hrtimer has been started in the time
between the releasing of the timekeeper lock and the IPI call (via a call to
on_each_cpu) in clock_was_set() in the do_settimeofday() code. The end result
is that a REALTIME_CLOCK timer has been added with softexpires = expires =
KTIME_MAX. The hrtimer_interrupt() fires/is called and the loop at
kernel/hrtimer.c:1289 is executed. In this loop the code subtracts the
clock base's offset (which was set to timekeeper->offs_real in
do_settimeofday()) from the current hrtimer_cpu_base->expiry value (which
was KTIME_MAX):
KTIME_MAX - (a negative value) = overflow
A simple check for an overflow can resolve this problem. Using KTIME_MAX
instead of the overflow value will result in the hrtimer function being run,
and the reprogramming of the timer after that.
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Reviewed-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Prarit Bhargava <prarit@redhat.com>
[jstultz: Tweaked commit subject]
Signed-off-by: John Stultz <john.stultz@linaro.org>
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We are planning to convert the dynticks Kconfig options layout
into a choice menu. The user must be able to easily pick
any of the following implementations: constant periodic tick,
idle dynticks, full dynticks.
As this implies a mutual exclusion, the two dynticks implementions
need to converge on the selection of a common Kconfig option in order
to ease the sharing of a common infrastructure.
It would thus seem pretty natural to reuse CONFIG_NO_HZ to
that end. It already implements all the idle dynticks code
and the full dynticks depends on all that code for now.
So ideally the choice menu would propose CONFIG_NO_HZ_IDLE and
CONFIG_NO_HZ_EXTENDED then both would select CONFIG_NO_HZ.
On the other hand we want to stay backward compatible: if
CONFIG_NO_HZ is set in an older config file, we want to
enable CONFIG_NO_HZ_IDLE by default.
But we can't afford both at the same time or we run into
a circular dependency:
1) CONFIG_NO_HZ_IDLE and CONFIG_NO_HZ_EXTENDED both select
CONFIG_NO_HZ
2) If CONFIG_NO_HZ is set, we default to CONFIG_NO_HZ_IDLE
We might be able to support that from Kconfig/Kbuild but it
may not be wise to introduce such a confusing behaviour.
So to solve this, create a new CONFIG_NO_HZ_COMMON option
which gathers the common code between idle and full dynticks
(that common code for now is simply the idle dynticks code)
and select it from their referring Kconfig.
Then we'll later create CONFIG_NO_HZ_IDLE and map CONFIG_NO_HZ
to it for backward compatibility.
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Geoff Levand <geoff@infradead.org>
Cc: Gilad Ben Yossef <gilad@benyossef.com>
Cc: Hakan Akkan <hakanakkan@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Kevin Hilman <khilman@linaro.org>
Cc: Li Zhong <zhong@linux.vnet.ibm.com>
Cc: Namhyung Kim <namhyung.kim@lge.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
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git://git.linaro.org/people/jstultz/linux into timers/core
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The current code makes the assumption that a cpu_base lock won't be
held if the CPU corresponding to that cpu_base is offline, which isn't
always true.
If a hrtimer is not queued, then it will not be migrated by
migrate_hrtimers() when a CPU is offlined. Therefore, the hrtimer's
cpu_base may still point to a CPU which has subsequently gone offline
if the timer wasn't enqueued at the time the CPU went down.
Normally this wouldn't be a problem, but a cpu_base's lock is blindly
reinitialized each time a CPU is brought up. If a CPU is brought
online during the period that another thread is performing a hrtimer
operation on a stale hrtimer, then the lock will be reinitialized
under its feet, and a SPIN_BUG() like the following will be observed:
<0>[ 28.082085] BUG: spinlock already unlocked on CPU#0, swapper/0/0
<0>[ 28.087078] lock: 0xc4780b40, value 0x0 .magic: dead4ead, .owner: <none>/-1, .owner_cpu: -1
<4>[ 42.451150] [<c0014398>] (unwind_backtrace+0x0/0x120) from [<c0269220>] (do_raw_spin_unlock+0x44/0xdc)
<4>[ 42.460430] [<c0269220>] (do_raw_spin_unlock+0x44/0xdc) from [<c071b5bc>] (_raw_spin_unlock+0x8/0x30)
<4>[ 42.469632] [<c071b5bc>] (_raw_spin_unlock+0x8/0x30) from [<c00a9ce0>] (__hrtimer_start_range_ns+0x1e4/0x4f8)
<4>[ 42.479521] [<c00a9ce0>] (__hrtimer_start_range_ns+0x1e4/0x4f8) from [<c00aa014>] (hrtimer_start+0x20/0x28)
<4>[ 42.489247] [<c00aa014>] (hrtimer_start+0x20/0x28) from [<c00e6190>] (rcu_idle_enter_common+0x1ac/0x320)
<4>[ 42.498709] [<c00e6190>] (rcu_idle_enter_common+0x1ac/0x320) from [<c00e6440>] (rcu_idle_enter+0xa0/0xb8)
<4>[ 42.508259] [<c00e6440>] (rcu_idle_enter+0xa0/0xb8) from [<c000f268>] (cpu_idle+0x24/0xf0)
<4>[ 42.516503] [<c000f268>] (cpu_idle+0x24/0xf0) from [<c06ed3c0>] (rest_init+0x88/0xa0)
<4>[ 42.524319] [<c06ed3c0>] (rest_init+0x88/0xa0) from [<c0c00978>] (start_kernel+0x3d0/0x434)
As an example, this particular crash occurred when hrtimer_start() was
executed on CPU #0. The code locked the hrtimer's current cpu_base
corresponding to CPU #1. CPU #0 then tried to switch the hrtimer's
cpu_base to an optimal CPU which was online. In this case, it selected
the cpu_base corresponding to CPU #3.
Before it could proceed, CPU #1 came online and reinitialized the
spinlock corresponding to its cpu_base. Thus now CPU #0 held a lock
which was reinitialized. When CPU #0 finally ended up unlocking the
old cpu_base corresponding to CPU #1 so that it could switch to CPU
#3, we hit this SPIN_BUG() above while in switch_hrtimer_base().
CPU #0 CPU #1
---- ----
... <offline>
hrtimer_start()
lock_hrtimer_base(base #1)
... init_hrtimers_cpu()
switch_hrtimer_base() ...
... raw_spin_lock_init(&cpu_base->lock)
raw_spin_unlock(&cpu_base->lock) ...
<spin_bug>
Solve this by statically initializing the lock.
Signed-off-by: Michael Bohan <mbohan@codeaurora.org>
Link: http://lkml.kernel.org/r/1363745965-23475-1-git-send-email-mbohan@codeaurora.org
Cc: stable@vger.kernel.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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The comments mention HRTIMER_ABS and HRTIMER_REL, these symbols don't
exist, the proper names are HRTIMER_MODE_ABS and HRTIMER_MODE_REL.
Signed-off-by: David Daney <david.daney@cavium.com>
Cc: Jiri Kosina <trivial@kernel.org>
Link: http://lkml.kernel.org/r/1363202438-21234-1-git-send-email-ddaney.cavm@gmail.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Add hrtimer support for CLOCK_TAI, as well as posix timer interfaces.
Signed-off-by: John Stultz <john.stultz@linaro.org>
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull timer changes from Ingo Molnar:
"Main changes:
- ntp: Add CONFIG_RTC_SYSTOHC: a generic RTC driver facility
complementing the existing CONFIG_RTC_HCTOSYS, which uses NTP to
keep the hardware clock updated.
- posix-timers: Fix clock_adjtime to always return timex data on
success. This is changing the ABI, but no breakage was expected
and found - caution is warranted nevertheless.
- platform persistent clock improvements/cleanups.
- clockevents: refactor timer broadcast handling to be more generic
and less duplicated with matching architecture code (mostly ARM
motivated.)
- various fixes and cleanups"
* 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
timers/x86/hpet: Use HPET_COUNTER to specify the hpet counter in vread_hpet()
posix-cpu-timers: Fix nanosleep task_struct leak
clockevents: Fix generic broadcast for FEAT_C3STOP
time, Fix setting of hardware clock in NTP code
hrtimer: Prevent hrtimer_enqueue_reprogram race
clockevents: Add generic timer broadcast function
clockevents: Add generic timer broadcast receiver
timekeeping: Switch HAS_PERSISTENT_CLOCK to ALWAYS_USE_PERSISTENT_CLOCK
x86/time/rtc: Don't print extended CMOS year when reading RTC
x86: Select HAS_PERSISTENT_CLOCK on x86
timekeeping: Add CONFIG_HAS_PERSISTENT_CLOCK option
rtc: Skip the suspend/resume handling if persistent clock exist
timekeeping: Add persistent_clock_exist flag
posix-timers: Fix clock_adjtime to always return timex data on success
Round the calculated scale factor in set_cyc2ns_scale()
NTP: Add a CONFIG_RTC_SYSTOHC configuration
MAINTAINERS: Update John Stultz's email
time: create __getnstimeofday for WARNless calls
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Move rt scheduler definitions out of include/linux/sched.h into
new file include/linux/sched/rt.h
Signed-off-by: Clark Williams <williams@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/20130207094707.7b9f825f@riff.lan
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Move the sysctl-related bits from include/linux/sched.h into
a new file: include/linux/sched/sysctl.h. Then update source
files requiring access to those bits by including the new
header file.
Signed-off-by: Clark Williams <williams@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/20130207094659.06dced96@riff.lan
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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hrtimer_enqueue_reprogram contains a race which could result in
timer.base switch during unlock/lock sequence.
hrtimer_enqueue_reprogram is releasing the lock protecting the timer
base for calling raise_softirq_irqsoff() due to a lock ordering issue
versus rq->lock.
If during that time another CPU calls __hrtimer_start_range_ns() on
the same hrtimer, the timer base might switch, before the current CPU
can lock base->lock again and therefor the unlock_timer_base() call
will unlock the wrong lock.
[ tglx: Added comment and massaged changelog ]
Signed-off-by: Leonid Shatz <leonid.shatz@ravellosystems.com>
Signed-off-by: Izik Eidus <izik.eidus@ravellosystems.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/1359981217-389-1-git-send-email-izik.eidus@ravellosystems.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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