linux-stable.git/kernel/sched/core.c, branch v3.12.57

sched/core: Remove false-positive warning from wake_up_process()

2016-03-03T11:45:58+00:00

commit 119d6f6a3be8b424b200dcee56e74484d5445f7e upstream.

Because wakeups can (fundamentally) be late, a task might not be in
the expected state. Therefore testing against a task's state is racy,
and can yield false positives.

Signed-off-by: Sasha Levin 
Signed-off-by: Peter Zijlstra (Intel) 
Acked-by: Linus Torvalds 
Cc: Mike Galbraith 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: oleg@redhat.com
Fixes: 9067ac85d533 ("wake_up_process() should be never used to wakeup a TASK_STOPPED/TRACED task")
Link: http://lkml.kernel.org/r/1448933660-23082-1-git-send-email-sasha.levin@oracle.com
Signed-off-by: Ingo Molnar 
Signed-off-by: Jiri Slaby

sched/core: Clear the root_domain cpumasks in init_rootdomain()

2016-03-03T11:45:58+00:00

commit 8295c69925ad53ec32ca54ac9fc194ff21bc40e2 upstream.

root_domain::rto_mask allocated through alloc_cpumask_var()
contains garbage data, this may cause problems. For instance,
When doing pull_rt_task(), it may do useless iterations if
rto_mask retains some extra garbage bits. Worse still, this
violates the isolated domain rule for clustered scheduling
using cpuset, because the tasks(with all the cpus allowed)
belongs to one root domain can be pulled away into another
root domain.

The patch cleans the garbage by using zalloc_cpumask_var()
instead of alloc_cpumask_var() for root_domain::rto_mask
allocation, thereby addressing the issues.

Do the same thing for root_domain's other cpumask memembers:
dlo_mask, span, and online.

Signed-off-by: Xunlei Pang 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: Linus Torvalds 
Cc: Mike Galbraith 
Cc: Peter Zijlstra 
Cc: Steven Rostedt 
Cc: Thomas Gleixner 
Link: http://lkml.kernel.org/r/1449057179-29321-1-git-send-email-xlpang@redhat.com
Signed-off-by: Ingo Molnar 
Signed-off-by: Jiri Slaby

sched: Allow balance callbacks for check_class_changed()

2016-03-03T11:45:54+00:00

commit 4c9a4bc89a9cca8128bce67d6bc8870d6b7ee0b2 upstream.

In order to remove dropping rq->lock from the
switched_{to,from}()/prio_changed() sched_class methods, run the
balance callbacks after it.

We need to remove dropping rq->lock because its buggy,
suppose using sched_setattr()/sched_setscheduler() to change a running
task from FIFO to OTHER.

By the time we get to switched_from_rt() the task is already enqueued
on the cfs runqueues. If switched_from_rt() does pull_rt_task() and
drops rq->lock, load-balancing can come in and move our task @p to
another rq.

The subsequent switched_to_fair() still assumes @p is on @rq and bad
things will happen.

By using balance callbacks we delay the load-balancing operations
{rt,dl}x{push,pull} until we've done all the important work and the
task is fully set up.

Furthermore, the balance callbacks do not know about @p, therefore
they cannot get confused like this.

Reported-by: Mike Galbraith 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: ktkhai@parallels.com
Cc: rostedt@goodmis.org
Cc: juri.lelli@gmail.com
Cc: pang.xunlei@linaro.org
Cc: oleg@redhat.com
Cc: wanpeng.li@linux.intel.com
Link: http://lkml.kernel.org/r/20150611124742.615343911@infradead.org
Signed-off-by: Thomas Gleixner 
Signed-off-by: Byungchul Park 
Signed-off-by: Jiri Slaby

sched: Replace post_schedule with a balance callback list

2016-03-03T11:45:54+00:00

commit e3fca9e7cbfb72694a21c886fcdf9f059cfded9c upstream.

Generalize the post_schedule() stuff into a balance callback list.
This allows us to more easily use it outside of schedule() and cross
sched_class.

Signed-off-by: Peter Zijlstra (Intel) 
Cc: ktkhai@parallels.com
Cc: rostedt@goodmis.org
Cc: juri.lelli@gmail.com
Cc: pang.xunlei@linaro.org
Cc: oleg@redhat.com
Cc: wanpeng.li@linux.intel.com
Cc: umgwanakikbuti@gmail.com
Link: http://lkml.kernel.org/r/20150611124742.424032725@infradead.org
Signed-off-by: Thomas Gleixner 
Signed-off-by: Byungchul Park 
Signed-off-by: Jiri Slaby

sched/core: Fix TASK_DEAD race in finish_task_switch()

2015-10-28T15:37:41+00:00

commit 95913d97914f44db2b81271c2e2ebd4d2ac2df83 upstream.

So the problem this patch is trying to address is as follows:

        CPU0                            CPU1

        context_switch(A, B)
                                        ttwu(A)
                                          LOCK A->pi_lock
                                          A->on_cpu == 0
        finish_task_switch(A)
          prev_state = A->state  <-.
          WMB                      |
          A->on_cpu = 0;           |
          UNLOCK rq0->lock         |
                                   |    context_switch(C, A)
                                   `--  A->state = TASK_DEAD
          prev_state == TASK_DEAD
            put_task_struct(A)
                                        context_switch(A, C)
                                        finish_task_switch(A)
                                          A->state == TASK_DEAD
                                            put_task_struct(A)

The argument being that the WMB will allow the load of A->state on CPU0
to cross over and observe CPU1's store of A->state, which will then
result in a double-drop and use-after-free.

Now the comment states (and this was true once upon a long time ago)
that we need to observe A->state while holding rq->lock because that
will order us against the wakeup; however the wakeup will not in fact
acquire (that) rq->lock; it takes A->pi_lock these days.

We can obviously fix this by upgrading the WMB to an MB, but that is
expensive, so we'd rather avoid that.

The alternative this patch takes is: smp_store_release(&A->on_cpu, 0),
which avoids the MB on some archs, but not important ones like ARM.

Reported-by: Oleg Nesterov 
Signed-off-by: Peter Zijlstra (Intel) 
Acked-by: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: linux-kernel@vger.kernel.org
Cc: manfred@colorfullife.com
Cc: will.deacon@arm.com
Fixes: e4a52bcb9a18 ("sched: Remove rq->lock from the first half of ttwu()")
Link: http://lkml.kernel.org/r/20150929124509.GG3816@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar 
Signed-off-by: Jiri Slaby

sched: Fix cpu_active_mask/cpu_online_mask race

2015-10-07T07:24:51+00:00

commit dd9d3843755da95f63dd3a376f62b3e45c011210 upstream.

There is a race condition in SMP bootup code, which may result
in

    WARNING: CPU: 0 PID: 1 at kernel/workqueue.c:4418
    workqueue_cpu_up_callback()
or
    kernel BUG at kernel/smpboot.c:135!

It can be triggered with a bit of luck in Linux guests running
on busy hosts.

	CPU0                        CPUn
	====                        ====

	_cpu_up()
	  __cpu_up()
				    start_secondary()
				      set_cpu_online()
					cpumask_set_cpu(cpu,
						   to_cpumask(cpu_online_bits));
	  cpu_notify(CPU_ONLINE)
	    
					cpumask_set_cpu(cpu,
						   to_cpumask(cpu_active_bits));

During the various CPU_ONLINE callbacks CPUn is online but not
active. Several things can go wrong at that point, depending on
the scheduling of tasks on CPU0.

Variant 1:

  cpu_notify(CPU_ONLINE)
    workqueue_cpu_up_callback()
      rebind_workers()
        set_cpus_allowed_ptr()

  This call fails because it requires an active CPU; rebind_workers()
  ends with a warning:

    WARNING: CPU: 0 PID: 1 at kernel/workqueue.c:4418
    workqueue_cpu_up_callback()

Variant 2:

  cpu_notify(CPU_ONLINE)
    smpboot_thread_call()
      smpboot_unpark_threads()
       ..
        __kthread_unpark()
          __kthread_bind()
          wake_up_state()
           ..
            select_task_rq()
              select_fallback_rq()

  The ->wake_cpu of the unparked thread is not allowed, making a call
  to select_fallback_rq() necessary. Then, select_fallback_rq() cannot
  find an allowed, active CPU and promptly resets the allowed CPUs, so
  that the task in question ends up on CPU0.

  When those unparked tasks are eventually executed, they run
  immediately into a BUG:

    kernel BUG at kernel/smpboot.c:135!

Just changing the order in which the online/active bits are set
(and adding some memory barriers), would solve the two issues
above. However, it would change the order of operations back to
the one before commit 6acbfb96976f ("sched: Fix hotplug vs.
set_cpus_allowed_ptr()"), thus, reintroducing that particular
problem.

Going further back into history, we have at least the following
commits touching this topic:
- commit 2baab4e90495 ("sched: Fix select_fallback_rq() vs cpu_active/cpu_online")
- commit 5fbd036b552f ("sched: Cleanup cpu_active madness")

Together, these give us the following non-working solutions:

  - secondary CPU sets active before online, because active is assumed to
    be a subset of online;

  - secondary CPU sets online before active, because the primary CPU
    assumes that an online CPU is also active;

  - secondary CPU sets online and waits for primary CPU to set active,
    because it might deadlock.

Commit 875ebe940d77 ("powerpc/smp: Wait until secondaries are
active & online") introduces an arch-specific solution to this
arch-independent problem.

Now, go for a more general solution without explicit waiting and
simply set active twice: once on the secondary CPU after online
was set and once on the primary CPU after online was seen.

set_cpus_allowed_ptr()")

Signed-off-by: Jan H. Schönherr 
Acked-by: Peter Zijlstra 
Cc: Anton Blanchard 
Cc: Borislav Petkov 
Cc: Joerg Roedel 
Cc: Linus Torvalds 
Cc: Matt Wilson 
Cc: Michael Ellerman 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Fixes: 6acbfb96976f ("sched: Fix hotplug vs. set_cpus_allowed_ptr()")
Link: http://lkml.kernel.org/r/1439408156-18840-1-git-send-email-jschoenh@amazon.de
Signed-off-by: Ingo Molnar 
Signed-off-by: Jiri Slaby

sched: Fix RLIMIT_RTTIME when PI-boosting to RT

2015-04-22T06:58:34+00:00

commit 746db9443ea57fd9c059f62c4bfbf41cf224fe13 upstream.

When non-realtime tasks get priority-inheritance boosted to a realtime
scheduling class, RLIMIT_RTTIME starts to apply to them. However, the
counter used for checking this (the same one used for SCHED_RR
timeslices) was not getting reset. This meant that tasks running with a
non-realtime scheduling class which are repeatedly boosted to a realtime
one, but never block while they are running realtime, eventually hit the
timeout without ever running for a time over the limit. This patch
resets the realtime timeslice counter when un-PI-boosting from an RT to
a non-RT scheduling class.

I have some test code with two threads and a shared PTHREAD_PRIO_INHERIT
mutex which induces priority boosting and spins while boosted that gets
killed by a SIGXCPU on non-fixed kernels but doesn't with this patch
applied. It happens much faster with a CONFIG_PREEMPT_RT kernel, and
does happen eventually with PREEMPT_VOLUNTARY kernels.

Signed-off-by: Brian Silverman 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: austin@peloton-tech.com
Link: http://lkml.kernel.org/r/1424305436-6716-1-git-send-email-brian@peloton-tech.com
Signed-off-by: Ingo Molnar 
Signed-off-by: Jiri Slaby

printk: rename printk_sched to printk_deferred

2014-08-19T12:23:37+00:00

commit aac74dc495456412c4130a1167ce4beb6c1f0b38 upstream.

After learning we'll need some sort of deferred printk functionality in
the timekeeping core, Peter suggested we rename the printk_sched function
so it can be reused by needed subsystems.

This only changes the function name. No logic changes.

Signed-off-by: John Stultz 
Reviewed-by: Steven Rostedt 
Cc: Jan Kara 
Cc: Peter Zijlstra 
Cc: Jiri Bohac 
Cc: Thomas Gleixner 
Cc: Ingo Molnar 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Jiri Slaby

sched: Fix hotplug vs. set_cpus_allowed_ptr()

2014-06-20T15:34:01+00:00

commit 6acbfb96976fc3350e30d964acb1dbbdf876d55e upstream.

Lai found that:

  WARNING: CPU: 1 PID: 13 at arch/x86/kernel/smp.c:124 native_smp_send_reschedule+0x2d/0x4b()
  ...
  migration_cpu_stop+0x1d/0x22

was caused by set_cpus_allowed_ptr() assuming that cpu_active_mask is
always a sub-set of cpu_online_mask.

This isn't true since 5fbd036b552f ("sched: Cleanup cpu_active madness").

So set active and online at the same time to avoid this particular
problem.

Fixes: 5fbd036b552f ("sched: Cleanup cpu_active madness")
Signed-off-by: Lai Jiangshan 
Signed-off-by: Peter Zijlstra 
Cc: Andrew Morton 
Cc: Gautham R. Shenoy 
Cc: Linus Torvalds 
Cc: Michael wang 
Cc: Paul Gortmaker 
Cc: Rafael J. Wysocki 
Cc: Srivatsa S. Bhat 
Cc: Toshi Kani 
Link: http://lkml.kernel.org/r/53758B12.8060609@cn.fujitsu.com
Signed-off-by: Ingo Molnar 
Signed-off-by: Jiri Slaby

sched: Assign correct scheduling domain to 'sd_llc'

2014-03-12T12:25:39+00:00

commit 5d4cf996cf134e8ddb4f906b8197feb9267c2b77 upstream.

Commit 42eb088e (sched: Avoid NULL dereference on sd_busy) corrected a NULL
dereference on sd_busy but the fix also altered what scheduling domain it
used for the 'sd_llc' percpu variable.

One impact of this is that a task selecting a runqueue may consider
idle CPUs that are not cache siblings as candidates for running.
Tasks are then running on CPUs that are not cache hot.

This was found through bisection where ebizzy threads were not seeing equal
performance and it looked like a scheduling fairness issue. This patch
mitigates but does not completely fix the problem on all machines tested
implying there may be an additional bug or a common root cause. Here are
the average range of performance seen by individual ebizzy threads. It
was tested on top of candidate patches related to x86 TLB range flushing.

	4-core machine
			    3.13.0-rc3            3.13.0-rc3
			       vanilla            fixsd-v3r3
	Mean   1        0.00 (  0.00%)        0.00 (  0.00%)
	Mean   2        0.34 (  0.00%)        0.10 ( 70.59%)
	Mean   3        1.29 (  0.00%)        0.93 ( 27.91%)
	Mean   4        7.08 (  0.00%)        0.77 ( 89.12%)
	Mean   5      193.54 (  0.00%)        2.14 ( 98.89%)
	Mean   6      151.12 (  0.00%)        2.06 ( 98.64%)
	Mean   7      115.38 (  0.00%)        2.04 ( 98.23%)
	Mean   8      108.65 (  0.00%)        1.92 ( 98.23%)

	8-core machine
	Mean   1         0.00 (  0.00%)        0.00 (  0.00%)
	Mean   2         0.40 (  0.00%)        0.21 ( 47.50%)
	Mean   3        23.73 (  0.00%)        0.89 ( 96.25%)
	Mean   4        12.79 (  0.00%)        1.04 ( 91.87%)
	Mean   5        13.08 (  0.00%)        2.42 ( 81.50%)
	Mean   6        23.21 (  0.00%)       69.46 (-199.27%)
	Mean   7        15.85 (  0.00%)      101.72 (-541.77%)
	Mean   8       109.37 (  0.00%)       19.13 ( 82.51%)
	Mean   12      124.84 (  0.00%)       28.62 ( 77.07%)
	Mean   16      113.50 (  0.00%)       24.16 ( 78.71%)

It's eliminated for one machine and reduced for another.

Signed-off-by: Mel Gorman 
Signed-off-by: Peter Zijlstra 
Cc: Alex Shi 
Cc: Andrew Morton 
Cc: Fengguang Wu 
Cc: H Peter Anvin 
Cc: Linus Torvalds 
Link: http://lkml.kernel.org/r/20131217092124.GV11295@suse.de
Signed-off-by: Ingo Molnar 
Signed-off-by: Jiri Slaby