Commit:

  2bacec8c ("sched: touch softlockup watchdog after idling")

introduced the touch_softlockup_watchdog_sched() call without
justification and I feel sched_clock management is not the right
place, it should only be concerned with producing semi coherent time.

If this causes watchdog thingies, we can find a better place.
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: NIngo Molnar <mingo@kernel.org>

The argument to sched_clock_idle_wakeup_event() has not been used in a
long time. Remove it.
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: NIngo Molnar <mingo@kernel.org>

Currently we keep sched_clock_tick() active for stable TSC in order to
keep the per-CPU state semi up-to-date. The (obvious) problem is that
by the time we detect TSC is borked, our per-CPU state is also borked.

So hook into the clocksource watchdog and call a method after we've
found it to still be stable.

There's the obvious race where the TSC goes wonky between finding it
stable and us running the callback, but closing that is too much work
and not really worth it, since we're already detecting TSC wobbles
after the fact, so we cannot, per definition, fully avoid funny clock
values.

And since the watchdog runs less often than the tick, this is also an
optimization.
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: NIngo Molnar <mingo@kernel.org>

In preparation for not keeping the sched_clock_tick() active for
stable TSC, we need to explicitly initialize all per-CPU state
before switching back to unstable.

Note: this patch looses the __gtod_offset calculation; it will be
restored in the next one.
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: NIngo Molnar <mingo@kernel.org>

When it is determined that the clock is actually unstable, and
we switch from stable to unstable, the __clear_sched_clock_stable()
function is eventually called.

In this function we set gtod_offset so the following holds true:

  sched_clock() + raw_offset == ktime_get_ns() + gtod_offset

But instead of getting the latest timestamps, we use the last values
from scd, so instead of sched_clock() we use scd->tick_raw, and
instead of ktime_get_ns() we use scd->tick_gtod.

However, later, when we use gtod_offset sched_clock_local() we do not
add it to scd->tick_gtod to calculate the correct clock value when we
determine the boundaries for min/max clocks.

This can result in tick granularity sched_clock() values, so fix it.
Signed-off-by: NPavel Tatashin <pasha.tatashin@oracle.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: hpa@zytor.com
Fixes: 5680d809 ("sched/clock: Provide better clock continuity")
Link: http://lkml.kernel.org/r/1490214265-899964-2-git-send-email-pasha.tatashin@oracle.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

People reported that commit:

  5680d809 ("sched/clock: Provide better clock continuity")

broke "perf test tsc".

That commit added another offset to the reported clock value; so
take that into account when computing the provided offset values.
Reported-by: NAdrian Hunter <adrian.hunter@intel.com>
Reported-by: NArnaldo Carvalho de Melo <acme@kernel.org>
Tested-by: NAlexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 5680d809 ("sched/clock: Provide better clock continuity")
Signed-off-by: NIngo Molnar <mingo@kernel.org>

Paul reported a problems with clear_sched_clock_stable(). Since we run
all of __clear_sched_clock_stable() from workqueue context, there's a
preempt problem.

Solve it by only running the static_key_disable() from workqueue.
Reported-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: fweisbec@gmail.com
Link: http://lkml.kernel.org/r/20170313124621.GA3328@twins.programming.kicks-ass.netSigned-off-by: NIngo Molnar <mingo@kernel.org>

We are going to move softlockup APIs out of <linux/sched.h>, which
will have to be picked up from other headers and a couple of .c files.

<linux/nmi.h> already includes <linux/sched.h>.

Include the <linux/nmi.h> header in the files that are going to need it.
Acked-by: NLinus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: NIngo Molnar <mingo@kernel.org>

We are going to split <linux/sched/clock.h> out of <linux/sched.h>, which
will have to be picked up from other headers and .c files.

Create a trivial placeholder <linux/sched/clock.h> file that just
maps to <linux/sched.h> to make this patch obviously correct and
bisectable.

Include the new header in the files that are going to need it.
Acked-by: NLinus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: NIngo Molnar <mingo@kernel.org>

Mike reported that he could trigger the WARN_ON_ONCE() in
set_sched_clock_stable() using hotplug.

This exposed a fundamental problem with the interface, we should never
mark the TSC stable if we ever find it to be unstable. Therefore
set_sched_clock_stable() is a broken interface.

The reason it existed is that not having it is a pain, it means all
relevant architecture code needs to call clear_sched_clock_stable()
where appropriate.

Of the three architectures that select HAVE_UNSTABLE_SCHED_CLOCK ia64
and parisc are trivial in that they never called
set_sched_clock_stable(), so add an unconditional call to
clear_sched_clock_stable() to them.

For x86 the story is a lot more involved, and what this patch tries to
do is ensure we preserve the status quo. So even is Cyrix or Transmeta
have usable TSC they never called set_sched_clock_stable() so they now
get an explicit mark unstable.
Reported-by: NMike Galbraith <efault@gmx.de>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 9881b024 ("sched/clock: Delay switching sched_clock to stable")
Link: http://lkml.kernel.org/r/20170119133633.GB6536@twins.programming.kicks-ass.netSigned-off-by: NIngo Molnar <mingo@kernel.org>

When switching between the unstable and stable variants it is
currently possible that clock discontinuities occur.

And while these will mostly be 'small', attempt to do better.

As observed on my IVB-EP, the sched_clock() is ~1.5s ahead of the
ktime_get_ns() based timeline at the point of switchover
(sched_clock_init_late()) after SMP bringup.

Equally, when the TSC is later found to be unstable -- typically
because SMM tries to hide its SMI latencies by mucking with the TSC --
we want to avoid large jumps.

Since the clocksource watchdog reports the issue after the fact we
cannot exactly fix up time, but since SMI latencies are typically
small (~10ns range), the discontinuity is mainly due to drift between
sched_clock() and ktime_get_ns() (which on my desktop is ~79s over
24days).

I dislike this patch because it adds overhead to the good case in
favour of dealing with badness. But given the widespread failure of
TSC stability this is worth it.

Note that in case the TSC makes drastic jumps after SMP bringup we're
still hosed. There's just not much we can do in that case without
stupid overhead.

If we were to somehow expose tsc_clocksource_reliable (which is hard
because this code is also used on ia64 and parisc) we could avoid some
of the newly introduced overhead.
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: NIngo Molnar <mingo@kernel.org>

Currently we switch to the stable sched_clock if we guess the TSC is
usable, and then switch back to the unstable path if it turns out TSC
isn't stable during SMP bringup after all.

Delay switching to the stable path until after SMP bringup is
complete. This way we'll avoid switching during the time we detect the
worst of the TSC offences.
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: NIngo Molnar <mingo@kernel.org>

sched_clock was still using the deprecated static_key interface.
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: NIngo Molnar <mingo@kernel.org>

The local_clock/cpu_clock functions were changed to prevent a double
identical test with sched_clock_cpu() when HAVE_UNSTABLE_SCHED_CLOCK
is set. That resulted in one line functions.

As these functions are in all the cases one line functions and in the
hot path, it is useful to specify them as static inline in order to
give a strong hint to the compiler.

After verification, it appears the compiler does not inline them
without this hint. Change those functions to static inline.

sched_clock_cpu() is called via the inlined local_clock()/cpu_clock()
functions from sched.h. So any module code including sched.h will
reference sched_clock_cpu(). Thus it must be exported with the
EXPORT_SYMBOL_GPL macro.
Signed-off-by: NDaniel Lezcano <daniel.lezcano@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1460385514-14700-2-git-send-email-daniel.lezcano@linaro.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

In case the HAVE_UNSTABLE_SCHED_CLOCK config is set, the cpu_clock() version
checks if sched_clock_stable() is not set and calls sched_clock_cpu(),
otherwise it calls sched_clock().

sched_clock_cpu() checks also if sched_clock_stable() is set and, if true,
calls sched_clock().

sched_clock() will be called in sched_clock_cpu() if sched_clock_stable() is
true.

Remove the duplicate test by directly calling sched_clock_cpu() and let the
static key act in this function instead.
Signed-off-by: NDaniel Lezcano <daniel.lezcano@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1460385514-14700-1-git-send-email-daniel.lezcano@linaro.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

Instead of checking sched_clock_stable from the nohz subsystem to verify
its tick dependency, migrate it to the new mask in order to include it
to the all-in-one check.
Reviewed-by: NChris Metcalf <cmetcalf@ezchip.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>

touch_softlockup_watchdog() is used to tell watchdog that scheduler
stall is expected.  One group of usage is from paths where the task
may not be able to yield for a long time such as performing slow PIO
to finicky device and coming out of suspend.  The other is to account
for scheduler and timer going idle.

For scheduler softlockup detection, there's no reason to distinguish
the two cases; however, workqueue lockup detector is planned and it
can use the same signals from the former group while the latter would
spuriously prevent detection.  This patch introduces a new function
touch_softlockup_watchdog_sched() and convert the latter group to call
it instead.  For now, it just calls touch_softlockup_watchdog() and
there's no functional difference.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrew Morton <akpm@linux-foundation.org>

There were still a number of references to my old Red Hat email
address in the kernel source. Remove these while keeping the
Red Hat copyright notices intact.
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

When the hypervisor pauses a virtualised kernel the kernel will observe a
jump in timebase, this can cause spurious messages from the softlockup
detector.

Whilst these messages are harmless, they are accompanied with a stack
trace which causes undue concern and more problematically the stack trace
in the guest has nothing to do with the observed problem and can only be
misleading.

Futhermore, on POWER8 this is completely avoidable with the introduction
of the Virtual Time Base (VTB) register.

This patch (of 2):

This permits the use of arch specific clocks for which virtualised kernels
can use their notion of 'running' time, not the elpased wall time which
will include host execution time.
Signed-off-by: NCyril Bur <cyrilbur@gmail.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Andrew Jones <drjones@redhat.com>
Acked-by: NDon Zickus <dzickus@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Cc: chai wen <chaiw.fnst@cn.fujitsu.com>
Cc: Fabian Frederick <fabf@skynet.be>
Cc: Aaron Tomlin <atomlin@redhat.com>
Cc: Ben Zhang <benzh@chromium.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Convert uses of __get_cpu_var for creating a address from a percpu
offset to this_cpu_ptr.

The two cases where get_cpu_var is used to actually access a percpu
variable are changed to use this_cpu_read/raw_cpu_read.
Reviewed-by: NThomas Gleixner <tglx@linutronix.de>
Signed-off-by: NChristoph Lameter <cl@linux.com>
Signed-off-by: NTejun Heo <tj@kernel.org>

To increase compiler portability there is <linux/compiler.h> which
provides convenience macros for various gcc constructs.  Eg: __weak for
__attribute__((weak)).  I've replaced all instances of gcc attributes
with the right macro in the kernel subsystem.
Signed-off-by: NGideon Israel Dsouza <gidisrael@gmail.com>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Prevent tracing of preempt_disable/enable() in sched_clock_cpu().
When CONFIG_DEBUG_PREEMPT is enabled, preempt_disable/enable() are
traced and this causes trace_clock() users (and probably others) to
go into an infinite recursion. Systems with a stable sched_clock()
are not affected.

This problem is similar to that fixed by upstream commit 95ef1e52
("KVM guest: prevent tracing recursion with kvmclock").
Signed-off-by: NFernando Luis Vazquez Cao <fernando@oss.ntt.co.jp>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Acked-by: NSteven Rostedt <rostedt@goodmis.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1394083528.4524.3.camel@nexusSigned-off-by: NIngo Molnar <mingo@kernel.org>

The code would assume sched_clock_stable() and switch to !stable
later, this switch brings a discontinuity in time.

The discontinuity on switching from stable to unstable was always
present, but previously we would set stable/unstable before
initializing TSC and usually stick to the one we start out with.

So the static_key bits brought an extra switch where there previously
wasn't one.

Things are further complicated by the fact that we cannot use
static_key as early as we usually call set_sched_clock_stable().

Fix things by tracking the stable state in a regular variable and only
set the static_key to the right state on sched_clock_init(), which is
ran right after late_time_init->tsc_init().

Before this we would not be using the TSC anyway.
Reported-and-Tested-by: NSasha Levin <sasha.levin@oracle.com>
Reported-by: dyoung@redhat.com
Fixes: 35af99e6 ("sched/clock, x86: Use a static_key for sched_clock_stable")
Cc: jacob.jun.pan@linux.intel.com
Cc: Mike Galbraith <bitbucket@online.de>
Cc: hpa@zytor.com
Cc: paulmck@linux.vnet.ibm.com
Cc: John Stultz <john.stultz@linaro.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: lenb@kernel.org
Cc: rjw@rjwysocki.net
Cc: Eliezer Tamir <eliezer.tamir@linux.intel.com>
Cc: rui.zhang@intel.com
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20140122115918.GG3694@twins.programming.kicks-ass.netSigned-off-by: NIngo Molnar <mingo@kernel.org>

The below tells us the static_key conversion has a problem; since the
exact point of clearing that flag isn't too important, delay the flip
and use a workqueue to process it.

[ ] TSC synchronization [CPU#0 -> CPU#22]:
[ ] Measured 8 cycles TSC warp between CPUs, turning off TSC clock.
[ ]
[ ] ======================================================
[ ] [ INFO: possible circular locking dependency detected ]
[ ] 3.13.0-rc3-01745-g848b0d0322cb-dirty #637 Not tainted
[ ] -------------------------------------------------------
[ ] swapper/0/1 is trying to acquire lock:
[ ]  (jump_label_mutex){+.+...}, at: [<ffffffff8115a637>] jump_label_lock+0x17/0x20
[ ]
[ ] but task is already holding lock:
[ ]  (cpu_hotplug.lock){+.+.+.}, at: [<ffffffff8109408b>] cpu_hotplug_begin+0x2b/0x60
[ ]
[ ] which lock already depends on the new lock.
[ ]
[ ]
[ ] the existing dependency chain (in reverse order) is:
[ ]
[ ] -> #1 (cpu_hotplug.lock){+.+.+.}:
[ ]        [<ffffffff810def00>] lock_acquire+0x90/0x130
[ ]        [<ffffffff81661f83>] mutex_lock_nested+0x63/0x3e0
[ ]        [<ffffffff81093fdc>] get_online_cpus+0x3c/0x60
[ ]        [<ffffffff8104cc67>] arch_jump_label_transform+0x37/0x130
[ ]        [<ffffffff8115a3cf>] __jump_label_update+0x5f/0x80
[ ]        [<ffffffff8115a48d>] jump_label_update+0x9d/0xb0
[ ]        [<ffffffff8115aa6d>] static_key_slow_inc+0x9d/0xb0
[ ]        [<ffffffff810c0f65>] sched_feat_set+0xf5/0x100
[ ]        [<ffffffff810c5bdc>] set_numabalancing_state+0x2c/0x30
[ ]        [<ffffffff81d12f3d>] numa_policy_init+0x1af/0x1b7
[ ]        [<ffffffff81cebdf4>] start_kernel+0x35d/0x41f
[ ]        [<ffffffff81ceb5a5>] x86_64_start_reservations+0x2a/0x2c
[ ]        [<ffffffff81ceb6a2>] x86_64_start_kernel+0xfb/0xfe
[ ]
[ ] -> #0 (jump_label_mutex){+.+...}:
[ ]        [<ffffffff810de141>] __lock_acquire+0x1701/0x1eb0
[ ]        [<ffffffff810def00>] lock_acquire+0x90/0x130
[ ]        [<ffffffff81661f83>] mutex_lock_nested+0x63/0x3e0
[ ]        [<ffffffff8115a637>] jump_label_lock+0x17/0x20
[ ]        [<ffffffff8115aa3b>] static_key_slow_inc+0x6b/0xb0
[ ]        [<ffffffff810ca775>] clear_sched_clock_stable+0x15/0x20
[ ]        [<ffffffff810503b3>] mark_tsc_unstable+0x23/0x70
[ ]        [<ffffffff810772cb>] check_tsc_sync_source+0x14b/0x150
[ ]        [<ffffffff81076612>] native_cpu_up+0x3a2/0x890
[ ]        [<ffffffff810941cb>] _cpu_up+0xdb/0x160
[ ]        [<ffffffff810942c9>] cpu_up+0x79/0x90
[ ]        [<ffffffff81d0af6b>] smp_init+0x60/0x8c
[ ]        [<ffffffff81cebf42>] kernel_init_freeable+0x8c/0x197
[ ]        [<ffffffff8164e32e>] kernel_init+0xe/0x130
[ ]        [<ffffffff8166beec>] ret_from_fork+0x7c/0xb0
[ ]
[ ] other info that might help us debug this:
[ ]
[ ]  Possible unsafe locking scenario:
[ ]
[ ]        CPU0                    CPU1
[ ]        ----                    ----
[ ]   lock(cpu_hotplug.lock);
[ ]                                lock(jump_label_mutex);
[ ]                                lock(cpu_hotplug.lock);
[ ]   lock(jump_label_mutex);
[ ]
[ ]  *** DEADLOCK ***
[ ]
[ ] 2 locks held by swapper/0/1:
[ ]  #0:  (cpu_add_remove_lock){+.+.+.}, at: [<ffffffff81094037>] cpu_maps_update_begin+0x17/0x20
[ ]  #1:  (cpu_hotplug.lock){+.+.+.}, at: [<ffffffff8109408b>] cpu_hotplug_begin+0x2b/0x60
[ ]
[ ] stack backtrace:
[ ] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.13.0-rc3-01745-g848b0d0322cb-dirty #637
[ ] Hardware name: Supermicro X8DTN/X8DTN, BIOS 4.6.3 01/08/2010
[ ]  ffffffff82c9c270 ffff880236843bb8 ffffffff8165c5f5 ffffffff82c9c270
[ ]  ffff880236843bf8 ffffffff81658c02 ffff880236843c80 ffff8802368586a0
[ ]  ffff880236858678 0000000000000001 0000000000000002 ffff880236858000
[ ] Call Trace:
[ ]  [<ffffffff8165c5f5>] dump_stack+0x4e/0x7a
[ ]  [<ffffffff81658c02>] print_circular_bug+0x1f9/0x207
[ ]  [<ffffffff810de141>] __lock_acquire+0x1701/0x1eb0
[ ]  [<ffffffff816680ff>] ? __atomic_notifier_call_chain+0x8f/0xb0
[ ]  [<ffffffff810def00>] lock_acquire+0x90/0x130
[ ]  [<ffffffff8115a637>] ? jump_label_lock+0x17/0x20
[ ]  [<ffffffff8115a637>] ? jump_label_lock+0x17/0x20
[ ]  [<ffffffff81661f83>] mutex_lock_nested+0x63/0x3e0
[ ]  [<ffffffff8115a637>] ? jump_label_lock+0x17/0x20
[ ]  [<ffffffff8115a637>] jump_label_lock+0x17/0x20
[ ]  [<ffffffff8115aa3b>] static_key_slow_inc+0x6b/0xb0
[ ]  [<ffffffff810ca775>] clear_sched_clock_stable+0x15/0x20
[ ]  [<ffffffff810503b3>] mark_tsc_unstable+0x23/0x70
[ ]  [<ffffffff810772cb>] check_tsc_sync_source+0x14b/0x150
[ ]  [<ffffffff81076612>] native_cpu_up+0x3a2/0x890
[ ]  [<ffffffff810941cb>] _cpu_up+0xdb/0x160
[ ]  [<ffffffff810942c9>] cpu_up+0x79/0x90
[ ]  [<ffffffff81d0af6b>] smp_init+0x60/0x8c
[ ]  [<ffffffff81cebf42>] kernel_init_freeable+0x8c/0x197
[ ]  [<ffffffff8164e320>] ? rest_init+0xd0/0xd0
[ ]  [<ffffffff8164e32e>] kernel_init+0xe/0x130
[ ]  [<ffffffff8166beec>] ret_from_fork+0x7c/0xb0
[ ]  [<ffffffff8164e320>] ? rest_init+0xd0/0xd0
[ ] ------------[ cut here ]------------
[ ] WARNING: CPU: 0 PID: 1 at /usr/src/linux-2.6/kernel/smp.c:374 smp_call_function_many+0xad/0x300()
[ ] Modules linked in:
[ ] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.13.0-rc3-01745-g848b0d0322cb-dirty #637
[ ] Hardware name: Supermicro X8DTN/X8DTN, BIOS 4.6.3 01/08/2010
[ ]  0000000000000009 ffff880236843be0 ffffffff8165c5f5 0000000000000000
[ ]  ffff880236843c18 ffffffff81093d8c 0000000000000000 0000000000000000
[ ]  ffffffff81ccd1a0 ffffffff810ca951 0000000000000000 ffff880236843c28
[ ] Call Trace:
[ ]  [<ffffffff8165c5f5>] dump_stack+0x4e/0x7a
[ ]  [<ffffffff81093d8c>] warn_slowpath_common+0x8c/0xc0
[ ]  [<ffffffff810ca951>] ? sched_clock_tick+0x1/0xa0
[ ]  [<ffffffff81093dda>] warn_slowpath_null+0x1a/0x20
[ ]  [<ffffffff8110b72d>] smp_call_function_many+0xad/0x300
[ ]  [<ffffffff8104f200>] ? arch_unregister_cpu+0x30/0x30
[ ]  [<ffffffff8104f200>] ? arch_unregister_cpu+0x30/0x30
[ ]  [<ffffffff810ca951>] ? sched_clock_tick+0x1/0xa0
[ ]  [<ffffffff8110ba96>] smp_call_function+0x46/0x80
[ ]  [<ffffffff8104f200>] ? arch_unregister_cpu+0x30/0x30
[ ]  [<ffffffff8110bb3c>] on_each_cpu+0x3c/0xa0
[ ]  [<ffffffff810ca950>] ? sched_clock_idle_sleep_event+0x20/0x20
[ ]  [<ffffffff810ca951>] ? sched_clock_tick+0x1/0xa0
[ ]  [<ffffffff8104f964>] text_poke_bp+0x64/0xd0
[ ]  [<ffffffff810ca950>] ? sched_clock_idle_sleep_event+0x20/0x20
[ ]  [<ffffffff8104ccde>] arch_jump_label_transform+0xae/0x130
[ ]  [<ffffffff8115a3cf>] __jump_label_update+0x5f/0x80
[ ]  [<ffffffff8115a48d>] jump_label_update+0x9d/0xb0
[ ]  [<ffffffff8115aa6d>] static_key_slow_inc+0x9d/0xb0
[ ]  [<ffffffff810ca775>] clear_sched_clock_stable+0x15/0x20
[ ]  [<ffffffff810503b3>] mark_tsc_unstable+0x23/0x70
[ ]  [<ffffffff810772cb>] check_tsc_sync_source+0x14b/0x150
[ ]  [<ffffffff81076612>] native_cpu_up+0x3a2/0x890
[ ]  [<ffffffff810941cb>] _cpu_up+0xdb/0x160
[ ]  [<ffffffff810942c9>] cpu_up+0x79/0x90
[ ]  [<ffffffff81d0af6b>] smp_init+0x60/0x8c
[ ]  [<ffffffff81cebf42>] kernel_init_freeable+0x8c/0x197
[ ]  [<ffffffff8164e320>] ? rest_init+0xd0/0xd0
[ ]  [<ffffffff8164e32e>] kernel_init+0xe/0x130
[ ]  [<ffffffff8166beec>] ret_from_fork+0x7c/0xb0
[ ]  [<ffffffff8164e320>] ? rest_init+0xd0/0xd0
[ ] ---[ end trace 6ff1df5620c49d26 ]---
[ ] tsc: Marking TSC unstable due to check_tsc_sync_source failed
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-v55fgqj3nnyqnngmvuu8ep6h@git.kernel.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

In order to avoid the runtime condition and variable load turn
sched_clock_stable into a static_key.

Also provide a shorter implementation of local_clock() and
cpu_clock(int) when sched_clock_stable==1.

                        MAINLINE   PRE       POST

    sched_clock_stable: 1          1         1
    (cold) sched_clock: 329841     221876    215295
    (cold) local_clock: 301773     234692    220773
    (warm) sched_clock: 38375      25602     25659
    (warm) local_clock: 100371     33265     27242
    (warm) rdtsc:       27340      24214     24208
    sched_clock_stable: 0          0         0
    (cold) sched_clock: 382634     235941    237019
    (cold) local_clock: 396890     297017    294819
    (warm) sched_clock: 38194      25233     25609
    (warm) local_clock: 143452     71234     71232
    (warm) rdtsc:       27345      24245     24243
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/n/tip-eummbdechzz37mwmpags1gjr@git.kernel.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

Now that x86 no longer requires IRQs disabled for sched_clock() and
ia64 never had this requirement (it doesn't seem to do cpufreq at
all), we can remove the requirement of disabling IRQs.

                        MAINLINE   PRE        POST

    sched_clock_stable: 1          1          1
    (cold) sched_clock: 329841     257223     221876
    (cold) local_clock: 301773     309889     234692
    (warm) sched_clock: 38375      25280      25602
    (warm) local_clock: 100371     85268      33265
    (warm) rdtsc:       27340      24247      24214
    sched_clock_stable: 0          0          0
    (cold) sched_clock: 382634     301224     235941
    (cold) local_clock: 396890     399870     297017
    (warm) sched_clock: 38194      25630      25233
    (warm) local_clock: 143452     129629     71234
    (warm) rdtsc:       27345      24307      24245
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/n/tip-36e5kohiasnr106d077mgubp@git.kernel.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

The sched_clock_remote() implementation has the following inatomicity
problem on 32bit systems when accessing the remote scd->clock, which
is a 64bit value.

CPU0			CPU1

sched_clock_local()	sched_clock_remote(CPU0)
...
			remote_clock = scd[CPU0]->clock
			    read_low32bit(scd[CPU0]->clock)
cmpxchg64(scd->clock,...)
			    read_high32bit(scd[CPU0]->clock)

While the update of scd->clock is using an atomic64 mechanism, the
readout on the remote cpu is not, which can cause completely bogus
readouts.

It is a quite rare problem, because it requires the update to hit the
narrow race window between the low/high readout and the update must go
across the 32bit boundary.

The resulting misbehaviour is, that CPU1 will see the sched_clock on
CPU1 ~4 seconds ahead of it's own and update CPU1s sched_clock value
to this bogus timestamp. This stays that way due to the clamping
implementation for about 4 seconds until the synchronization with
CLOCK_MONOTONIC undoes the problem.

The issue is hard to observe, because it might only result in a less
accurate SCHED_OTHER timeslicing behaviour. To create observable
damage on realtime scheduling classes, it is necessary that the bogus
update of CPU1 sched_clock happens in the context of an realtime
thread, which then gets charged 4 seconds of RT runtime, which results
in the RT throttler mechanism to trigger and prevent scheduling of RT
tasks for a little less than 4 seconds. So this is quite unlikely as
well.

The issue was quite hard to decode as the reproduction time is between
2 days and 3 weeks and intrusive tracing makes it less likely, but the
following trace recorded with trace_clock=global, which uses
sched_clock_local(), gave the final hint:

  <idle>-0   0d..30 400269.477150: hrtimer_cancel: hrtimer=0xf7061e80
  <idle>-0   0d..30 400269.477151: hrtimer_start:  hrtimer=0xf7061e80 ...
irq/20-S-587 1d..32 400273.772118: sched_wakeup:   comm= ... target_cpu=0
  <idle>-0   0dN.30 400273.772118: hrtimer_cancel: hrtimer=0xf7061e80

What happens is that CPU0 goes idle and invokes
sched_clock_idle_sleep_event() which invokes sched_clock_local() and
CPU1 runs a remote wakeup for CPU0 at the same time, which invokes
sched_remote_clock(). The time jump gets propagated to CPU0 via
sched_remote_clock() and stays stale on both cores for ~4 seconds.

There are only two other possibilities, which could cause a stale
sched clock:

1) ktime_get() which reads out CLOCK_MONOTONIC returns a sporadic
   wrong value.

2) sched_clock() which reads the TSC returns a sporadic wrong value.

#1 can be excluded because sched_clock would continue to increase for
   one jiffy and then go stale.

#2 can be excluded because it would not make the clock jump
   forward. It would just result in a stale sched_clock for one jiffy.

After quite some brain twisting and finding the same pattern on other
traces, sched_clock_remote() remained the only place which could cause
such a problem and as explained above it's indeed racy on 32bit
systems.

So while on 64bit systems the readout is atomic, we need to verify the
remote readout on 32bit machines. We need to protect the local->clock
readout in sched_clock_remote() on 32bit as well because an NMI could
hit between the low and the high readout, call sched_clock_local() and
modify local->clock.

Thanks to Siegfried Wulsch for bearing with my debug requests and
going through the tedious tasks of running a bunch of reproducer
systems to generate the debug information which let me decode the
issue.
Reported-by: NSiegfried Wulsch <Siegfried.Wulsch@rovema.de>
Acked-by: NPeter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/alpine.LFD.2.02.1304051544160.21884@ionosSigned-off-by: NThomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org

There's too many sched*.[ch] files in kernel/, give them their own
directory.

(No code changed, other than Makefile glue added.)
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

The changed files were only including linux/module.h for the
EXPORT_SYMBOL infrastructure, and nothing else.  Revector them
onto the isolated export header for faster compile times.

Nothing to see here but a whole lot of instances of:

  -#include <linux/module.h>
  +#include <linux/export.h>

This commit is only changing the kernel dir; next targets
will probably be mm, fs, the arch dirs, etc.
Signed-off-by: NPaul Gortmaker <paul.gortmaker@windriver.com>

Add more clock information to /proc/sched_debug, Thomas wanted to see
the sched_clock_stable state.
Requested-by: NThomas Gleixner <tglx@linutronix.de>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

For people who otherwise get to write: cpu_clock(smp_processor_id()),
there is now: local_clock().

Also, as per suggestion from Andrew, provide some documentation on
the various clock interfaces, and minimize the unsigned long long vs
u64 mess.
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Jens Axboe <jaxboe@fusionio.com>
LKML-Reference: <1275052414.1645.52.camel@laptop>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

After merging the block tree, 20100414's linux-next build (x86_64
allmodconfig) failed like this:

ERROR: "get_gendisk" [block/blk-cgroup.ko] undefined!
ERROR: "sched_clock" [block/blk-cgroup.ko] undefined!

This happens because the two symbols aren't exported and hence not available
when blk-cgroup code is built as a module. I've tried to stay consistent with
the use of EXPORT_SYMBOL or EXPORT_SYMBOL_GPL with the other symbols in the
respective files.
Signed-off-by: NDivyesh Shah <dpshah@google.com>
Acked-by: NGui Jianfeng <guijianfeng@cn.fujitsu.cn>
Signed-off-by: NJens Axboe <jens.axboe@oracle.com>

Relax stable-sched-clock architectures to not save/disable/restore
hardirqs in cpu_clock().

The background is that I was trying to resolve a sparc64 perf
issue when I discovered this problem.

On sparc64 I implement pseudo NMIs by simply running the kernel
at IRQ level 14 when local_irq_disable() is called, this allows
performance counter events to still come in at IRQ level 15.

This doesn't work if any code in an NMI handler does
local_irq_save() or local_irq_disable() since the "disable" will
kick us back to cpu IRQ level 14 thus letting NMIs back in and
we recurse.

The only path which that does that in the perf event IRQ
handling path is the code supporting frequency based events.  It
uses cpu_clock().

cpu_clock() simply invokes sched_clock() with IRQs disabled.

And that's a fundamental bug all on it's own, particularly for
the HAVE_UNSTABLE_SCHED_CLOCK case.  NMIs can thus get into the
sched_clock() code interrupting the local IRQ disable code
sections of it.

Furthermore, for the not-HAVE_UNSTABLE_SCHED_CLOCK case, the IRQ
disabling done by cpu_clock() is just pure overhead and
completely unnecessary.

So the core problem is that sched_clock() is not NMI safe, but
we are invoking it from NMI contexts in the perf events code
(via cpu_clock()).

A less important issue is the overhead of IRQ disabling when it
isn't necessary in cpu_clock().

CONFIG_HAVE_UNSTABLE_SCHED_CLOCK architectures are not
affected by this patch.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>
Acked-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
LKML-Reference: <20091213.182502.215092085.davem@davemloft.net>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Commit def0a9b2 (sched_clock: Make it NMI safe) assumed
cmpxchg() of 64bit values was available on X86_32.

That is not so - and causes some subtle scheduler misbehavior due
to incorrect timestamps off to up by ~4 seconds.

Two symptoms are known right now:

 - interactivity problems seen by Arjan: up to 600 msecs
   latencies instead of the expected 20-40 msecs. These
   latencies are very visible on the desktop.

 - incorrect CPU stats: occasionally too high percentages in 'top',
   and crazy CPU usage stats.
Reported-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: NEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: NArjan van de Ven <arjan@linux.intel.com>
Acked-by: NLinus Torvalds <torvalds@linux-foundation.org>
Cc: John Stultz <johnstul@us.ibm.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20090930170754.0886ff2e@infradead.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Arjan complained about the suckyness of TSC on modern machines, and
asked if we could do something about that for PERF_SAMPLE_TIME.

Make cpu_clock() NMI safe by removing the spinlock and using
cmpxchg. This also makes it smaller and more robust.

Affects architectures that use HAVE_UNSTABLE_SCHED_CLOCK, i.e. IA64
and x86.
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Account for the initial offset to the jiffy count.

[ Impact: fix printk timestamps on architectures using fallback sched_clock() ]
Signed-off-by: NRon Lee <ron@debian.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

- remove superfluous checks in __update_sched_clock()
- skip sched_clock_tick() for sched_clock_stable
- reinstate the simple !HAVE_UNSTABLE_SCHED_CLOCK code to please the bloatwatch
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Allow CONFIG_HAVE_UNSTABLE_SCHED_CLOCK architectures to still specify
that their sched_clock() implementation is reliable.

This will be used by x86 to switch on a faster sched_clock_cpu()
implementation on certain CPU types.
Signed-off-by: NIngo Molnar <mingo@elte.hu>

make sure we dont execute more complex sched_clock() code in NMI context.
Acked-by: NPeter Zijlstra <peterz@infradead.org>
Acked-by: NSteven Rostedt <rostedt@goodmis.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Redo:

  5b7dba4f: sched_clock: prevent scd->clock from moving backwards

which had to be reverted due to s2ram hangs:

  ca7e716c: Revert "sched_clock: prevent scd->clock from moving backwards"

... this time with resume restoring GTOD later in the sequence
taken into account as well.

The "timekeeping_suspended" flag is not very nice but we cannot call into
GTOD before it has been properly resumed and the scheduler will run very
early in the resume sequence.

Cc: <stable@kernel.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>