linux-stable.git/kernel/sched, branch linux-4.5.y

sched/loadavg: Fix loadavg artifacts on fully idle and on fully loaded systems

2016-06-01T19:16:58+00:00

commit 20878232c52329f92423d27a60e48b6a6389e0dd upstream.

Systems show a minimal load average of 0.00, 0.01, 0.05 even when they
have no load at all.

Uptime and /proc/loadavg on all systems with kernels released during the
last five years up until kernel version 4.6-rc5, show a 5- and 15-minute
minimum loadavg of 0.01 and 0.05 respectively. This should be 0.00 on
idle systems, but the way the kernel calculates this value prevents it
from getting lower than the mentioned values.

Likewise but not as obviously noticeable, a fully loaded system with no
processes waiting, shows a maximum 1/5/15 loadavg of 1.00, 0.99, 0.95
(multiplied by number of cores).

Once the (old) load becomes 93 or higher, it mathematically can never
get lower than 93, even when the active (load) remains 0 forever.
This results in the strange 0.00, 0.01, 0.05 uptime values on idle
systems.  Note: 93/2048 = 0.0454..., which rounds up to 0.05.

It is not correct to add a 0.5 rounding (=1024/2048) here, since the
result from this function is fed back into the next iteration again,
so the result of that +0.5 rounding value then gets multiplied by
(2048-2037), and then rounded again, so there is a virtual "ghost"
load created, next to the old and active load terms.

By changing the way the internally kept value is rounded, that internal
value equivalent now can reach 0.00 on idle, and 1.00 on full load. Upon
increasing load, the internally kept load value is rounded up, when the
load is decreasing, the load value is rounded down.

The modified code was tested on nohz=off and nohz kernels. It was tested
on vanilla kernel 4.6-rc5 and on centos 7.1 kernel 3.10.0-327. It was
tested on single, dual, and octal cores system. It was tested on virtual
hosts and bare hardware. No unwanted effects have been observed, and the
problems that the patch intended to fix were indeed gone.

Tested-by: Damien Wyart 
Signed-off-by: Vik Heyndrickx 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: Doug Smythies 
Cc: Linus Torvalds 
Cc: Mike Galbraith 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Fixes: 0f004f5a696a ("sched: Cure more NO_HZ load average woes")
Link: http://lkml.kernel.org/r/e8d32bff-d544-7748-72b5-3c86cc71f09f@veribox.net
Signed-off-by: Ingo Molnar 
Signed-off-by: Greg Kroah-Hartman

sched/cgroup: Fix/cleanup cgroup teardown/init

2016-05-04T21:49:00+00:00

commit 2f5177f0fd7e531b26d54633be62d1d4cb94621c upstream.

The CPU controller hasn't kept up with the various changes in the whole
cgroup initialization / destruction sequence, and commit:

  2e91fa7f6d45 ("cgroup: keep zombies associated with their original cgroups")

caused it to explode.

The reason for this is that zombies do not inhibit css_offline() from
being called, but do stall css_released(). Now we tear down the cfs_rq
structures on css_offline() but zombies can run after that, leading to
use-after-free issues.

The solution is to move the tear-down to css_released(), which
guarantees nobody (including no zombies) is still using our cgroup.

Furthermore, a few simple cleanups are possible too. There doesn't
appear to be any point to us using css_online() (anymore?) so fold that
in css_alloc().

And since cgroup code guarantees an RCU grace period between
css_released() and css_free() we can forgo using call_rcu() and free the
stuff immediately.

Suggested-by: Tejun Heo 
Reported-by: Kazuki Yamaguchi 
Reported-by: Niklas Cassel 
Tested-by: Niklas Cassel 
Signed-off-by: Peter Zijlstra (Intel) 
Acked-by: Tejun Heo 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Fixes: 2e91fa7f6d45 ("cgroup: keep zombies associated with their original cgroups")
Link: http://lkml.kernel.org/r/20160316152245.GY6344@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar 
Signed-off-by: Greg Kroah-Hartman

sched/cputime: Fix steal time accounting vs. CPU hotplug

2016-04-12T14:33:49+00:00

commit e9532e69b8d1d1284e8ecf8d2586de34aec61244 upstream.

On CPU hotplug the steal time accounting can keep a stale rq->prev_steal_time
value over CPU down and up. So after the CPU comes up again the delta
calculation in steal_account_process_tick() wreckages itself due to the
unsigned math:

	 u64 steal = paravirt_steal_clock(smp_processor_id());

	 steal -= this_rq()->prev_steal_time;

So if steal is smaller than rq->prev_steal_time we end up with an insane large
value which then gets added to rq->prev_steal_time, resulting in a permanent
wreckage of the accounting. As a consequence the per CPU stats in /proc/stat
become stale.

Nice trick to tell the world how idle the system is (100%) while the CPU is
100% busy running tasks. Though we prefer realistic numbers.

None of the accounting values which use a previous value to account for
fractions is reset at CPU hotplug time. update_rq_clock_task() has a sanity
check for prev_irq_time and prev_steal_time_rq, but that sanity check solely
deals with clock warps and limits the /proc/stat visible wreckage. The
prev_time values are still wrong.

Solution is simple: Reset rq->prev_*_time when the CPU is plugged in again.

Signed-off-by: Thomas Gleixner 
Acked-by: Rik van Riel 
Cc: Frederic Weisbecker 
Cc: Glauber Costa 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Fixes: commit 095c0aa83e52 "sched: adjust scheduler cpu power for stolen time"
Fixes: commit aa483808516c "sched: Remove irq time from available CPU power"
Fixes: commit e6e6685accfa "KVM guest: Steal time accounting"
Link: http://lkml.kernel.org/r/alpine.DEB.2.11.1603041539490.3686@nanos
Signed-off-by: Ingo Molnar 
Signed-off-by: Greg Kroah-Hartman

sched/fair: Avoid using decay_load_missed() with a negative value

2016-04-12T14:33:14+00:00

commit 7400d3bbaa229eb8e7631d28fb34afd7cd2c96ff upstream.

decay_load_missed() cannot handle nagative values, so we need to prevent
using the function with a negative value.

Reported-by: Dietmar Eggemann 
Signed-off-by: Byungchul Park 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: Chris Metcalf 
Cc: Christoph Lameter 
Cc: Frederic Weisbecker 
Cc: Linus Torvalds 
Cc: Luiz Capitulino 
Cc: Mike Galbraith 
Cc: Paul E . McKenney 
Cc: Peter Zijlstra 
Cc: Rik van Riel 
Cc: Thomas Gleixner 
Cc: perterz@infradead.org
Fixes: 59543275488d ("sched/fair: Prepare __update_cpu_load() to handle active tickless")
Link: http://lkml.kernel.org/r/20160115070749.GA1914@X58A-UD3R
Signed-off-by: Ingo Molnar 
Signed-off-by: Greg Kroah-Hartman

sched/cputime: Fix steal_account_process_tick() to always return jiffies

2016-04-12T14:33:14+00:00

commit f9c904b7613b8b4c85b10cd6b33ad41b2843fa9d upstream.

The callers of steal_account_process_tick() expect it to return
whether a jiffy should be considered stolen or not.

Currently the return value of steal_account_process_tick() is in
units of cputime, which vary between either jiffies or nsecs
depending on CONFIG_VIRT_CPU_ACCOUNTING_GEN.

If cputime has nsecs granularity and there is a tiny amount of
stolen time (a few nsecs, say) then we will consider the entire
tick stolen and will not account the tick on user/system/idle,
causing /proc/stats to show invalid data.

The fix is to change steal_account_process_tick() to accumulate
the stolen time and only account it once it's worth a jiffy.

(Thanks to Frederic Weisbecker for suggestions to fix a bug in my
first version of the patch.)

Signed-off-by: Chris Friesen 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Thomas Gleixner 
Cc: Frederic Weisbecker 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Link: http://lkml.kernel.org/r/56DBBDB8.40305@mail.usask.ca
Signed-off-by: Ingo Molnar 
Signed-off-by: Greg Kroah-Hartman

sched/kasan: remove stale KASAN poison after hotplug

2016-03-09T23:43:42+00:00

Functions which the compiler has instrumented for KASAN place poison on
the stack shadow upon entry and remove this poision prior to returning.

In the case of CPU hotplug, CPUs exit the kernel a number of levels deep
in C code.  Any instrumented functions on this critical path will leave
portions of the stack shadow poisoned.

When a CPU is subsequently brought back into the kernel via a different
path, depending on stackframe, layout calls to instrumented functions
may hit this stale poison, resulting in (spurious) KASAN splats to the
console.

To avoid this, clear any stale poison from the idle thread for a CPU
prior to bringing a CPU online.

Signed-off-by: Mark Rutland 
Acked-by: Catalin Marinas 
Reviewed-by: Andrey Ryabinin 
Reviewed-by: Ingo Molnar 
Cc: Alexander Potapenko 
Cc: Lorenzo Pieralisi 
Cc: Peter Zijlstra 
Cc: Will Deacon 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

sched/deadline: Fix trivial typo in printk() message

2016-02-17T09:02:00+00:00

It's "too much" not "to much".

Signed-off-by: Steven Rostedt 
Acked-by: Juri Lelli 
Cc: Jiri Kosina 
Cc: Juri Lelli 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Link: http://lkml.kernel.org/r/20160210120422.4ca77e68@gandalf.local.home
Signed-off-by: Ingo Molnar

Merge branch 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2016-01-31T23:44:04+00:00

Pull scheduler fixes from Thomas Gleixner:
 "Three small fixes in the scheduler/core:

   - use after free in the numa code
   - crash in the numa init code
   - a simple spelling fix"

* 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  pid: Fix spelling in comments
  sched/numa: Fix use-after-free bug in the task_numa_compare
  sched: Fix crash in sched_init_numa()

Merge branches 'pm-cpuidle', 'pm-cpufreq', 'pm-domains' and 'pm-sleep'

2016-01-29T20:45:17+00:00

* pm-cpuidle:
  cpuidle: coupled: remove unused define cpuidle_coupled_lock
  cpuidle: fix fallback mechanism for suspend to idle in absence of enter_freeze

* pm-cpufreq:
  cpufreq: cpufreq-dt: avoid uninitialized variable warnings:
  cpufreq: pxa2xx: fix pxa_cpufreq_change_voltage prototype
  cpufreq: Use list_is_last() to check last entry of the policy list
  cpufreq: Fix NULL reference crash while accessing policy->governor_data

* pm-domains:
  PM / Domains: Fix typo in comment
  PM / Domains: Fix potential deadlock while adding/removing subdomains
  PM / domains: fix lockdep issue for all subdomains

* pm-sleep:
  PM: APM_EMULATION does not depend on PM

wrappers for ->i_mutex access

2016-01-22T23:04:28+00:00

parallel to mutex_{lock,unlock,trylock,is_locked,lock_nested},
inode_foo(inode) being mutex_foo(&inode->i_mutex).

Please, use those for access to ->i_mutex; over the coming cycle
->i_mutex will become rwsem, with ->lookup() done with it held
only shared.

Signed-off-by: Al Viro