linux.git/kernel/sched, branch v4.9-rc3

Merge branches 'core-urgent-for-linus', 'irq-urgent-for-linus' and 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2016-10-28T17:12:27+00:00

Pull objtool, irq and scheduler fixes from Ingo Molnar:
 "One more objtool fixlet for GCC6 code generation patterns, an irq
  DocBook fix and an unused variable warning fix in the scheduler"

* 'core-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  objtool: Fix rare switch jump table pattern detection

* 'irq-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  doc: Add missing parameter for msi_setup

* 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched/fair: Remove unused but set variable 'rq'

mm: remove per-zone hashtable of bitlock waitqueues

2016-10-27T16:27:57+00:00

The per-zone waitqueues exist because of a scalability issue with the
page waitqueues on some NUMA machines, but it turns out that they hurt
normal loads, and now with the vmalloced stacks they also end up
breaking gfs2 that uses a bit_wait on a stack object:

     wait_on_bit(&gh->gh_iflags, HIF_WAIT, TASK_UNINTERRUPTIBLE)

where 'gh' can be a reference to the local variable 'mount_gh' on the
stack of fill_super().

The reason the per-zone hash table breaks for this case is that there is
no "zone" for virtual allocations, and trying to look up the physical
page to get at it will fail (with a BUG_ON()).

It turns out that I actually complained to the mm people about the
per-zone hash table for another reason just a month ago: the zone lookup
also hurts the regular use of "unlock_page()" a lot, because the zone
lookup ends up forcing several unnecessary cache misses and generates
horrible code.

As part of that earlier discussion, we had a much better solution for
the NUMA scalability issue - by just making the page lock have a
separate contention bit, the waitqueue doesn't even have to be looked at
for the normal case.

Peter Zijlstra already has a patch for that, but let's see if anybody
even notices.  In the meantime, let's fix the actual gfs2 breakage by
simplifying the bitlock waitqueues and removing the per-zone issue.

Reported-by: Andreas Gruenbacher 
Tested-by: Bob Peterson 
Acked-by: Mel Gorman 
Cc: Peter Zijlstra 
Cc: Andy Lutomirski 
Cc: Steven Whitehouse 
Signed-off-by: Linus Torvalds

sched/fair: Remove unused but set variable 'rq'

2016-10-27T06:33:52+00:00

Since commit:

  8663e24d56dc ("sched/fair: Reorder cgroup creation code")

... the variable 'rq' in alloc_fair_sched_group() is set but no longer used.
Remove it to fix the following GCC warning when building with 'W=1':

  kernel/sched/fair.c:8842:13: warning: variable ‘rq’ set but not used [-Wunused-but-set-variable]

Signed-off-by: Tobias Klauser 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Link: http://lkml.kernel.org/r/20161026113704.8981-1-tklauser@distanz.ch
Signed-off-by: Ingo Molnar

sched/fair: Fix incorrect task group ->load_avg

2016-10-19T13:04:47+00:00

A scheduler performance regression has been reported by Joseph Salisbury,
which he bisected back to:

  3d30544f0212 ("sched/fair: Apply more PELT fixes)

The regression triggers when several levels of task groups are involved
(read: SystemD) and cpu_possible_mask != cpu_present_mask.

The root cause is that group entity's load (tg_child->se[i]->avg.load_avg)
is initialized to scale_load_down(se->load.weight). During the creation of
a child task group, its group entities on possible CPUs are attached to
parent's cfs_rq (tg_parent) and their loads are added to the parent's load
(tg_parent->load_avg) with update_tg_load_avg().

But only the load on online CPUs will then be updated to reflect real load,
whereas load on other CPUs will stay at the initial value.

The result is a tg_parent->load_avg that is higher than the real load, the
weight of group entities (tg_parent->se[i]->load.weight) on online CPUs is
smaller than it should be, and the task group gets a less running time than
what it could expect.

( This situation can be detected with /proc/sched_debug. The ".tg_load_avg"
  of the task group will be much higher than sum of ".tg_load_avg_contrib"
  of online cfs_rqs of the task group. )

The load of group entities don't have to be intialized to something else
than 0 because their load will increase when an entity is attached.

Reported-by: Joseph Salisbury 
Tested-by: Dietmar Eggemann 
Signed-off-by: Vincent Guittot 
Acked-by: Peter Zijlstra 
Cc:  # 4.8.x
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: joonwoop@codeaurora.org
Fixes: 3d30544f0212 ("sched/fair: Apply more PELT fixes)
Link: http://lkml.kernel.org/r/1476881123-10159-1-git-send-email-vincent.guittot@linaro.org
Signed-off-by: Ingo Molnar

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

2016-10-18T16:53:59+00:00

Pull scheduler fix from Ingo Molnar:
 "Fix a crash that can trigger when racing with CPU hotplug: we didn't
  use sched-domains data structures carefully enough in select_idle_cpu()"

* 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched/fair: Fix sched domains NULL dereference in select_idle_sibling()

Merge tag 'gcc-plugins-v4.9-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux

2016-10-15T17:03:15+00:00

Pull gcc plugins update from Kees Cook:
 "This adds a new gcc plugin named "latent_entropy". It is designed to
  extract as much possible uncertainty from a running system at boot
  time as possible, hoping to capitalize on any possible variation in
  CPU operation (due to runtime data differences, hardware differences,
  SMP ordering, thermal timing variation, cache behavior, etc).

  At the very least, this plugin is a much more comprehensive example
  for how to manipulate kernel code using the gcc plugin internals"

* tag 'gcc-plugins-v4.9-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
  latent_entropy: Mark functions with __latent_entropy
  gcc-plugins: Add latent_entropy plugin

Merge branch 'for-4.9' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup

2016-10-14T19:18:50+00:00

Pull cgroup updates from Tejun Heo:

 - tracepoints for basic cgroup management operations added

 - kernfs and cgroup path formatting functions updated to behave in the
   style of strlcpy()

 - non-critical bug fixes

* 'for-4.9' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
  blkcg: Unlock blkcg_pol_mutex only once when cpd == NULL
  cgroup: fix error handling regressions in proc_cgroup_show() and cgroup_release_agent()
  cpuset: fix error handling regression in proc_cpuset_show()
  cgroup: add tracepoints for basic operations
  cgroup: make cgroup_path() and friends behave in the style of strlcpy()
  kernfs: remove kernfs_path_len()
  kernfs: make kernfs_path*() behave in the style of strlcpy()
  kernfs: add dummy implementation of kernfs_path_from_node()

sched/fair: Fix sched domains NULL dereference in select_idle_sibling()

2016-10-11T08:40:06+00:00

Commit:

  10e2f1acd01 ("sched/core: Rewrite and improve select_idle_siblings()")

... improved select_idle_sibling(), but also triggered a regression (crash)
during CPU-hotplug:

  BUG: unable to handle kernel NULL pointer dereference at 0000000000000078
  IP: [] select_idle_sibling+0x1c2/0x4f0
  Call Trace:
   
    select_task_rq_fair+0x749/0x930
    ? select_task_rq_fair+0xb4/0x930
    ? __lock_is_held+0x54/0x70
    try_to_wake_up+0x19a/0x5b0
    default_wake_function+0x12/0x20
    autoremove_wake_function+0x12/0x40
    __wake_up_common+0x55/0x90
    __wake_up+0x39/0x50
    wake_up_klogd_work_func+0x40/0x60
    irq_work_run_list+0x57/0x80
    irq_work_run+0x2c/0x30
    smp_irq_work_interrupt+0x2e/0x40
    irq_work_interrupt+0x96/0xa0
   
    ? _raw_spin_unlock_irqrestore+0x45/0x80
    try_to_wake_up+0x4a/0x5b0
    wake_up_state+0x10/0x20
    __kthread_unpark+0x67/0x70
    kthread_unpark+0x22/0x30
    cpuhp_online_idle+0x3e/0x70
    cpu_startup_entry+0x6a/0x450
    start_secondary+0x154/0x180

This can be reproduced by running the ftrace test case of kselftest, the
test case will hot-unplug the CPU and the CPU will attach to the NULL
sched-domain during scheduler teardown.

The step 2 for the rewrite select_idle_siblings():

  | Step 2) tracks the average cost of the scan and compares this to the
  | average idle time guestimate for the CPU doing the wakeup.

If the CPU which doing the wakeup is the going hot-unplug CPU, then NULL
sched domain will be dereferenced to acquire the average cost of the scan.

This patch fix it by failing the search of an idle CPU in the LLC process
if this sched domain is NULL.

Tested-by: Catalin Marinas 
Signed-off-by: Wanpeng Li 
Cc: Linus Torvalds 
Cc: Mike Galbraith 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Link: http://lkml.kernel.org/r/1475971443-3187-1-git-send-email-wanpeng.li@hotmail.com
Signed-off-by: Ingo Molnar

latent_entropy: Mark functions with __latent_entropy

2016-10-10T21:51:45+00:00

The __latent_entropy gcc attribute can be used only on functions and
variables.  If it is on a function then the plugin will instrument it for
gathering control-flow entropy. If the attribute is on a variable then
the plugin will initialize it with random contents.  The variable must
be an integer, an integer array type or a structure with integer fields.

These specific functions have been selected because they are init
functions (to help gather boot-time entropy), are called at unpredictable
times, or they have variable loops, each of which provide some level of
latent entropy.

Signed-off-by: Emese Revfy 
[kees: expanded commit message]
Signed-off-by: Kees Cook

nmi_backtrace: generate one-line reports for idle cpus

2016-10-08T01:46:30+00:00

When doing an nmi backtrace of many cores, most of which are idle, the
output is a little overwhelming and very uninformative.  Suppress
messages for cpus that are idling when they are interrupted and just
emit one line, "NMI backtrace for N skipped: idling at pc 0xNNN".

We do this by grouping all the cpuidle code together into a new
.cpuidle.text section, and then checking the address of the interrupted
PC to see if it lies within that section.

This commit suitably tags x86 and tile idle routines, and only adds in
the minimal framework for other architectures.

Link: http://lkml.kernel.org/r/1472487169-14923-5-git-send-email-cmetcalf@mellanox.com
Signed-off-by: Chris Metcalf 
Acked-by: Peter Zijlstra (Intel) 
Tested-by: Peter Zijlstra (Intel) 
Tested-by: Daniel Thompson  [arm]
Tested-by: Petr Mladek 
Cc: Aaron Tomlin 
Cc: Peter Zijlstra (Intel) 
Cc: "Rafael J. Wysocki" 
Cc: Russell King 
Cc: Thomas Gleixner 
Cc: Ingo Molnar 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds