linux-stable.git/kernel/sched/core.c, branch v4.4.19

kernel/sysrq, watchdog, sched/core: Reset watchdog on all CPUs while processing sysrq-w

2016-08-10T09:49:25+00:00

commit 57675cb976eff977aefb428e68e4e0236d48a9ff upstream.

Lengthy output of sysrq-w may take a lot of time on slow serial console.

Currently we reset NMI-watchdog on the current CPU to avoid spurious
lockup messages. Sometimes this doesn't work since softlockup watchdog
might trigger on another CPU which is waiting for an IPI to proceed.
We reset softlockup watchdogs on all CPUs, but we do this only after
listing all tasks, and this may be too late on a busy system.

So, reset watchdogs CPUs earlier, in for_each_process_thread() loop.

Signed-off-by: Andrey Ryabinin 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Link: http://lkml.kernel.org/r/1465474805-14641-1-git-send-email-aryabinin@virtuozzo.com
Signed-off-by: Ingo Molnar 
Signed-off-by: Greg Kroah-Hartman

sched: panic on corrupted stack end

2016-06-24T17:18:20+00:00

commit 29d6455178a09e1dc340380c582b13356227e8df upstream.

Until now, hitting this BUG_ON caused a recursive oops (because oops
handling involves do_exit(), which calls into the scheduler, which in
turn raises an oops), which caused stuff below the stack to be
overwritten until a panic happened (e.g.  via an oops in interrupt
context, caused by the overwritten CPU index in the thread_info).

Just panic directly.

Signed-off-by: Jann Horn 
Signed-off-by: Linus Torvalds 
Signed-off-by: Greg Kroah-Hartman

sched/cgroup: Fix/cleanup cgroup teardown/init

2016-05-04T21:48:42+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

2016-04-12T16:09:05+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: Fix crash in sched_init_numa()

2016-02-17T20:31:02+00:00

commit 9c03ee147193645be4c186d3688232fa438c57c7 upstream.

The following PowerPC commit:

  c118baf80256 ("arch/powerpc/mm/numa.c: do not allocate bootmem memory for non existing nodes")

avoids allocating bootmem memory for non existent nodes.

But when DEBUG_PER_CPU_MAPS=y is enabled, my powerNV system failed to boot
because in sched_init_numa(), cpumask_or() operation was done on
unallocated nodes.

Fix that by making cpumask_or() operation only on existing nodes.

[ Tested with and w/o DEBUG_PER_CPU_MAPS=y on x86 and PowerPC. ]

Reported-by: Jan Stancek 
Tested-by: Jan Stancek 
Signed-off-by: Raghavendra K T 
Cc: 
Cc: 
Cc: 
Cc: 
Cc: 
Cc: 
Cc: 
Cc: 
Cc: 
Cc: 
Cc: 
Link: http://lkml.kernel.org/r/1452884483-11676-1-git-send-email-raghavendra.kt@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar 
Signed-off-by: Greg Kroah-Hartman

Merge branch 'master' into for-4.4-fixes

2015-12-07T15:09:03+00:00

The following commit which went into mainline through networking tree

  3b13758f51de ("cgroups: Allow dynamically changing net_classid")

conflicts in net/core/netclassid_cgroup.c with the following pending
fix in cgroup/for-4.4-fixes.

  1f7dd3e5a6e4 ("cgroup: fix handling of multi-destination migration from subtree_control enabling")

The former separates out update_classid() from cgrp_attach() and
updates it to walk all fds of all tasks in the target css so that it
can be used from both migration and config change paths.  The latter
drops @css from cgrp_attach().

Resolve the conflict by making cgrp_attach() call update_classid()
with the css from the first task.  We can revive @tset walking in
cgrp_attach() but given that net_cls is v1 only where there always is
only one target css during migration, this is fine.

Signed-off-by: Tejun Heo 
Reported-by: Stephen Rothwell 
Cc: Nina Schiff

sched/core: Fix an SMP ordering race in try_to_wake_up() vs. schedule()

2015-12-04T09:26:43+00:00

Oleg noticed that its possible to falsely observe p->on_cpu == 0 such
that we'll prematurely continue with the wakeup and effectively run p on
two CPUs at the same time.

Even though the overlap is very limited; the task is in the middle of
being scheduled out; it could still result in corruption of the
scheduler data structures.

        CPU0                            CPU1

        set_current_state(...)

        
          context_switch(X, Y)
            prepare_lock_switch(Y)
              Y->on_cpu = 1;
            finish_lock_switch(X)
              store_release(X->on_cpu, 0);

                                        try_to_wake_up(X)
                                          LOCK(p->pi_lock);

                                          t = X->on_cpu; // 0

          context_switch(Y, X)
            prepare_lock_switch(X)
              X->on_cpu = 1;
            finish_lock_switch(Y)
              store_release(Y->on_cpu, 0);
        

        schedule();
          deactivate_task(X);
          X->on_rq = 0;

                                          if (X->on_rq) // false

                                          if (t) while (X->on_cpu)
                                            cpu_relax();

          context_switch(X, ..)
            finish_lock_switch(X)
              store_release(X->on_cpu, 0);

Avoid the load of X->on_cpu being hoisted over the X->on_rq load.

Reported-by: Oleg Nesterov 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: Linus Torvalds 
Cc: Mike Galbraith 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Signed-off-by: Ingo Molnar

sched/core: Better document the try_to_wake_up() barriers

2015-12-04T09:26:42+00:00

Explain how the control dependency and smp_rmb() end up providing
ACQUIRE semantics and pair with smp_store_release() in
finish_lock_switch().

Signed-off-by: Peter Zijlstra (Intel) 
Cc: Linus Torvalds 
Cc: Mike Galbraith 
Cc: Oleg Nesterov 
Cc: Paul E. McKenney 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Signed-off-by: Ingo Molnar

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

2015-12-04T09:16:21+00:00

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: 
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

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

2015-12-04T09:10:16+00:00

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