linux-stable.git/kernel/sched, branch v3.18.10

sched/autogroup: Fix failure to set cpu.rt_runtime_us

2015-03-24T01:02:53+00:00

commit 1fe89e1b6d270aa0d3452c60d38461ea589594e3 upstream.

Because task_group() uses a cache of autogroup_task_group(), whose
output depends on sched_class, switching classes can generate
problems.

In particular, when started as fair, the cache points to the
autogroup, so when switching to RT the tg_rt_schedulable() test fails
for every cpu.rt_{runtime,period}_us change because now the autogroup
has tasks and no runtime.

Furthermore, going back to the previous semantics of varying
task_group() with sched_class has the down-side that the sched_debug
output varies as well, even though the task really is in the
autogroup.

Therefore add an autogroup exception to tg_has_rt_tasks() -- such that
both (all) task_group() usages in sched/core now have one. And remove
all the remnants of the variable task_group() output.

Reported-by: Zefan Li 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: Linus Torvalds 
Cc: Mike Galbraith 
Cc: Stefan Bader 
Fixes: 8323f26ce342 ("sched: Fix race in task_group()")
Link: http://lkml.kernel.org/r/20150209112237.GR5029@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar 
Signed-off-by: Greg Kroah-Hartman

sched: Fix hrtick_start() on UP

2015-03-24T01:02:52+00:00

commit 868933359a3bdda25b562e9d41bce7071edc1b08 upstream.

The commit 177ef2a6315e ("sched/deadline: Fix a precision problem in
the microseconds range") forgot to change the UP version of
hrtick_start(), do so now.

Signed-off-by: Wanpeng Li 
Fixes: 177ef2a6315e ("sched/deadline: Fix a precision problem in the microseconds range")
[ Fixed the changelog. ]
Signed-off-by: Peter Zijlstra (Intel) 
Cc: Juri Lelli 
Cc: Kirill Tkhai 
Cc: Linus Torvalds 
Link: http://lkml.kernel.org/r/1416962647-76792-7-git-send-email-wanpeng.li@linux.intel.com
Signed-off-by: Ingo Molnar 
Signed-off-by: Greg Kroah-Hartman

sched: Add missing rcu protection to wake_up_all_idle_cpus

2015-01-16T14:59:54+00:00

commit fd7de1e8d5b2b2b35e71332fafb899f584597150 upstream.

Locklessly doing is_idle_task(rq->curr) is only okay because of
RCU protection.  The older variant of the broken code checked
rq->curr == rq->idle instead and therefore didn't need RCU.

Fixes: f6be8af1c95d ("sched: Add new API wake_up_if_idle() to wake up the idle cpu")
Signed-off-by: Andy Lutomirski 
Reviewed-by: Chuansheng Liu 
Cc: Peter Zijlstra 
Link: http://lkml.kernel.org/r/729365dddca178506dfd0a9451006344cd6808bc.1417277372.git.luto@amacapital.net
Signed-off-by: Ingo Molnar 
Signed-off-by: Greg Kroah-Hartman

sched/deadline: Avoid double-accounting in case of missed deadlines

2015-01-16T14:59:54+00:00

commit 269ad8015a6b2bb1cf9e684da4921eb6fa0a0c88 upstream.

The dl_runtime_exceeded() function is supposed to ckeck if
a SCHED_DEADLINE task must be throttled, by checking if its
current runtime is <= 0. However, it also checks if the
scheduling deadline has been missed (the current time is
larger than the current scheduling deadline), further
decreasing the runtime if this happens.
This "double accounting" is wrong:

- In case of partitioned scheduling (or single CPU), this
  happens if task_tick_dl() has been called later than expected
  (due to small HZ values). In this case, the current runtime is
  also negative, and replenish_dl_entity() can take care of the
  deadline miss by recharging the current runtime to a value smaller
  than dl_runtime

- In case of global scheduling on multiple CPUs, scheduling
  deadlines can be missed even if the task did not consume more
  runtime than expected, hence penalizing the task is wrong

This patch fix this problem by throttling a SCHED_DEADLINE task
only when its runtime becomes negative, and not modifying the runtime

Signed-off-by: Luca Abeni 
Signed-off-by: Peter Zijlstra (Intel) 
Acked-by: Juri Lelli 
Cc: Dario Faggioli 
Cc: Linus Torvalds 
Link: http://lkml.kernel.org/r/1418813432-20797-3-git-send-email-luca.abeni@unitn.it
Signed-off-by: Ingo Molnar 
Signed-off-by: Greg Kroah-Hartman

sched/deadline: Fix migration of SCHED_DEADLINE tasks

2015-01-16T14:59:54+00:00

commit 6a503c3be937d275113b702e0421e5b0720abe8a upstream.

According to global EDF, tasks should be migrated between runqueues
without checking if their scheduling deadlines and runtimes are valid.
However, SCHED_DEADLINE currently performs such a check:
a migration happens doing:

	deactivate_task(rq, next_task, 0);
	set_task_cpu(next_task, later_rq->cpu);
	activate_task(later_rq, next_task, 0);

which ends up calling dequeue_task_dl(), setting the new CPU, and then
calling enqueue_task_dl().

enqueue_task_dl() then calls enqueue_dl_entity(), which calls
update_dl_entity(), which can modify scheduling deadline and runtime,
breaking global EDF scheduling.

As a result, some of the properties of global EDF are not respected:
for example, a taskset {(30, 80), (40, 80), (120, 170)} scheduled on
two cores can have unbounded response times for the third task even
if 30/80+40/80+120/170 = 1.5809 < 2

This can be fixed by invoking update_dl_entity() only in case of
wakeup, or if this is a new SCHED_DEADLINE task.

Signed-off-by: Luca Abeni 
Signed-off-by: Peter Zijlstra (Intel) 
Acked-by: Juri Lelli 
Cc: Dario Faggioli 
Cc: Linus Torvalds 
Link: http://lkml.kernel.org/r/1418813432-20797-2-git-send-email-luca.abeni@unitn.it
Signed-off-by: Ingo Molnar 
Signed-off-by: Greg Kroah-Hartman

context_tracking: Restore previous state in schedule_user

2014-12-04T04:55:58+00:00

It appears that some SCHEDULE_USER (asm for schedule_user) callers
in arch/x86/kernel/entry_64.S are called from RCU kernel context,
and schedule_user will return in RCU user context.  This causes RCU
warnings and possible failures.

This is intended to be a minimal fix suitable for 3.18.

Reported-and-tested-by: Dave Jones 
Cc: Oleg Nesterov 
Cc: Frédéric Weisbecker 
Acked-by: Paul E. McKenney 
Signed-off-by: Andy Lutomirski 
Signed-off-by: Linus Torvalds

sched: Provide update_curr callbacks for stop/idle scheduling classes

2014-11-23T22:14:40+00:00

Chris bisected a NULL pointer deference in task_sched_runtime() to
commit 6e998916dfe3 'sched/cputime: Fix clock_nanosleep()/clock_gettime()
inconsistency'.

Chris observed crashes in atop or other /proc walking programs when he
started fork bombs on his machine.  He assumed that this is a new exit
race, but that does not make any sense when looking at that commit.

What's interesting is that, the commit provides update_curr callbacks
for all scheduling classes except stop_task and idle_task.

While nothing can ever hit that via the clock_nanosleep() and
clock_gettime() interfaces, which have been the target of the commit in
question, the author obviously forgot that there are other code paths
which invoke task_sched_runtime()

do_task_stat(()
 thread_group_cputime_adjusted()
   thread_group_cputime()
     task_cputime()
       task_sched_runtime()
        if (task_current(rq, p) && task_on_rq_queued(p)) {
          update_rq_clock(rq);
          up->sched_class->update_curr(rq);
        }

If the stats are read for a stomp machine task, aka 'migration/N' and
that task is current on its cpu, this will happily call the NULL pointer
of stop_task->update_curr.  Ooops.

Chris observation that this happens faster when he runs the fork bomb
makes sense as the fork bomb will kick migration threads more often so
the probability to hit the issue will increase.

Add the missing update_curr callbacks to the scheduler classes stop_task
and idle_task.  While idle tasks cannot be monitored via /proc we have
other means to hit the idle case.

Fixes: 6e998916dfe3 'sched/cputime: Fix clock_nanosleep()/clock_gettime() inconsistency'
Reported-by: Chris Mason 
Reported-and-tested-by: Borislav Petkov 
Signed-off-by: Thomas Gleixner 
Cc: Ingo Molnar 
Cc: Stanislaw Gruszka 
Cc: Peter Zijlstra 
Signed-off-by: Linus Torvalds

sched/cputime: Fix clock_nanosleep()/clock_gettime() inconsistency

2014-11-16T09:04:20+00:00

Commit d670ec13178d0 "posix-cpu-timers: Cure SMP wobbles" fixes one glibc
test case in cost of breaking another one. After that commit, calling
clock_nanosleep(TIMER_ABSTIME, X) and then clock_gettime(&Y) can result
of Y time being smaller than X time.

Reproducer/tester can be found further below, it can be compiled and ran by:

	gcc -o tst-cpuclock2 tst-cpuclock2.c -pthread
	while ./tst-cpuclock2 ; do : ; done

This reproducer, when running on a buggy kernel, will complain
about "clock_gettime difference too small".

Issue happens because on start in thread_group_cputimer() we initialize
sum_exec_runtime of cputimer with threads runtime not yet accounted and
then add the threads runtime to running cputimer again on scheduler
tick, making it's sum_exec_runtime bigger than actual threads runtime.

KOSAKI Motohiro posted a fix for this problem, but that patch was never
applied: https://lkml.org/lkml/2013/5/26/191 .

This patch takes different approach to cure the problem. It calls
update_curr() when cputimer starts, that assure we will have updated
stats of running threads and on the next schedule tick we will account
only the runtime that elapsed from cputimer start. That also assure we
have consistent state between cpu times of individual threads and cpu
time of the process consisted by those threads.

Full reproducer (tst-cpuclock2.c):

	#define _GNU_SOURCE
	#include 
	#include 
	#include 
	#include 
	#include 
	#include 
	#include 

	/* Parameters for the Linux kernel ABI for CPU clocks.  */
	#define CPUCLOCK_SCHED          2
	#define MAKE_PROCESS_CPUCLOCK(pid, clock) \
		((~(clockid_t) (pid) << 3) | (clockid_t) (clock))

	static pthread_barrier_t barrier;

	/* Help advance the clock.  */
	static void *chew_cpu(void *arg)
	{
		pthread_barrier_wait(&barrier);
		while (1) ;

		return NULL;
	}

	/* Don't use the glibc wrapper.  */
	static int do_nanosleep(int flags, const struct timespec *req)
	{
		clockid_t clock_id = MAKE_PROCESS_CPUCLOCK(0, CPUCLOCK_SCHED);

		return syscall(SYS_clock_nanosleep, clock_id, flags, req, NULL);
	}

	static int64_t tsdiff(const struct timespec *before, const struct timespec *after)
	{
		int64_t before_i = before->tv_sec * 1000000000ULL + before->tv_nsec;
		int64_t after_i = after->tv_sec * 1000000000ULL + after->tv_nsec;

		return after_i - before_i;
	}

	int main(void)
	{
		int result = 0;
		pthread_t th;

		pthread_barrier_init(&barrier, NULL, 2);

		if (pthread_create(&th, NULL, chew_cpu, NULL) != 0) {
			perror("pthread_create");
			return 1;
		}

		pthread_barrier_wait(&barrier);

		/* The test.  */
		struct timespec before, after, sleeptimeabs;
		int64_t sleepdiff, diffabs;
		const struct timespec sleeptime = {.tv_sec = 0,.tv_nsec = 100000000 };

		/* The relative nanosleep.  Not sure why this is needed, but its presence
		   seems to make it easier to reproduce the problem.  */
		if (do_nanosleep(0, &sleeptime) != 0) {
			perror("clock_nanosleep");
			return 1;
		}

		/* Get the current time.  */
		if (clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &before) < 0) {
			perror("clock_gettime[2]");
			return 1;
		}

		/* Compute the absolute sleep time based on the current time.  */
		uint64_t nsec = before.tv_nsec + sleeptime.tv_nsec;
		sleeptimeabs.tv_sec = before.tv_sec + nsec / 1000000000;
		sleeptimeabs.tv_nsec = nsec % 1000000000;

		/* Sleep for the computed time.  */
		if (do_nanosleep(TIMER_ABSTIME, &sleeptimeabs) != 0) {
			perror("absolute clock_nanosleep");
			return 1;
		}

		/* Get the time after the sleep.  */
		if (clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &after) < 0) {
			perror("clock_gettime[3]");
			return 1;
		}

		/* The time after sleep should always be equal to or after the absolute sleep
		   time passed to clock_nanosleep.  */
		sleepdiff = tsdiff(&sleeptimeabs, &after);
		if (sleepdiff < 0) {
			printf("absolute clock_nanosleep woke too early: %" PRId64 "\n", sleepdiff);
			result = 1;

			printf("Before %llu.%09llu\n", before.tv_sec, before.tv_nsec);
			printf("After  %llu.%09llu\n", after.tv_sec, after.tv_nsec);
			printf("Sleep  %llu.%09llu\n", sleeptimeabs.tv_sec, sleeptimeabs.tv_nsec);
		}

		/* The difference between the timestamps taken before and after the
		   clock_nanosleep call should be equal to or more than the duration of the
		   sleep.  */
		diffabs = tsdiff(&before, &after);
		if (diffabs < sleeptime.tv_nsec) {
			printf("clock_gettime difference too small: %" PRId64 "\n", diffabs);
			result = 1;
		}

		pthread_cancel(th);

		return result;
	}

Signed-off-by: Stanislaw Gruszka 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: Rik van Riel 
Cc: Frederic Weisbecker 
Cc: KOSAKI Motohiro 
Cc: Oleg Nesterov 
Cc: Linus Torvalds 
Link: http://lkml.kernel.org/r/20141112155843.GA24803@redhat.com
Signed-off-by: Ingo Molnar

sched/cputime: Fix cpu_timer_sample_group() double accounting

2014-11-16T09:04:18+00:00

While looking over the cpu-timer code I found that we appear to add
the delta for the calling task twice, through:

  cpu_timer_sample_group()
    thread_group_cputimer()
      thread_group_cputime()
        times->sum_exec_runtime += task_sched_runtime();

    *sample = cputime.sum_exec_runtime + task_delta_exec();

Which would make the sample run ahead, making the sleep short.

Signed-off-by: Peter Zijlstra (Intel) 
Cc: KOSAKI Motohiro 
Cc: Oleg Nesterov 
Cc: Stanislaw Gruszka 
Cc: Christoph Lameter 
Cc: Frederic Weisbecker 
Cc: Linus Torvalds 
Cc: Rik van Riel 
Cc: Tejun Heo 
Link: http://lkml.kernel.org/r/20141112113737.GI10476@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar

sched/numa: Avoid selecting oneself as swap target

2014-11-16T09:04:17+00:00

Because the whole numa task selection stuff runs with preemption
enabled (its long and expensive) we can end up migrating and selecting
oneself as a swap target. This doesn't really work out well -- we end
up trying to acquire the same lock twice for the swap migrate -- so
avoid this.

Reported-and-Tested-by: Sasha Levin 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: Linus Torvalds 
Link: http://lkml.kernel.org/r/20141110100328.GF29390@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar