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  1. 16 Oct, 2013 3 commits
    • Peter Zijlstra's avatar
      sched: Remove get_online_cpus() usage · 6acce3ef
      Peter Zijlstra authored 
      Remove get_online_cpus() usage from the scheduler; there's 4 sites that
use it:

 - sched_init_smp(); where its completely superfluous since we're in
   'early' boot and there simply cannot be any hotplugging.

 - sched_getaffinity(); we already take a raw spinlock to protect the
   task cpus_allowed mask, this disables preemption and therefore
   also stabilizes cpu_online_mask as that's modified using
   stop_machine. However switch to active mask for symmetry with
   sched_setaffinity()/set_cpus_allowed_ptr(). We guarantee active
   mask stability by inserting sync_rcu/sched() into _cpu_down.

 - sched_setaffinity(); we don't appear to need get_online_cpus()
   either, there's two sites where hotplug appears relevant:
    * cpuset_cpus_allowed(); for the !cpuset case we use possible_mask,
      for the cpuset case we hold task_lock, which is a spinlock and
      thus for mainline disables preemption (might cause pain on RT).
    * set_cpus_allowed_ptr(); Holds all scheduler locks and thus has
      preemption properly disabled; also it already deals with hotplug
      races explicitly where it releases them.

 - migrate_swap(); we can make stop_two_cpus() do the heavy lifting for
   us with a little trickery. By adding a sync_sched/rcu() after the
   CPU_DOWN_PREPARE notifier we can provide preempt/rcu guarantees for
   cpu_active_mask. Use these to validate that both our cpus are active
   when queueing the stop work before we queue the stop_machine works
   for take_cpu_down().
Signed-off-by: default avatarPeter Zijlstra <peterz@infradead.org>
Cc: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Link: http://lkml.kernel.org/r/20131011123820.GV3081@twins.programming.kicks-ass.netSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
      6acce3ef
    • Peter Zijlstra's avatar
      sched: Fix race in migrate_swap_stop() · 74602315
      Peter Zijlstra authored 
      There is a subtle race in migrate_swap, when task P, on CPU A, decides to swap
places with task T, on CPU B.

Task P:
  - call migrate_swap
Task T:
  - go to sleep, removing itself from the runqueue
Task P:
  - double lock the runqueues on CPU A & B
Task T:
  - get woken up, place itself on the runqueue of CPU C
Task P:
  - see that task T is on a runqueue, and pretend to remove it
    from the runqueue on CPU B

Now CPUs B & C both have corrupted scheduler data structures.

This patch fixes it, by holding the pi_lock for both of the tasks
involved in the migrate swap. This prevents task T from waking up,
and placing itself onto another runqueue, until after migrate_swap
has released all locks.

This means that, when migrate_swap checks, task T will be either
on the runqueue where it was originally seen, or not on any
runqueue at all. Migrate_swap deals correctly with of those cases.
Tested-by: default avatarJoe Mario <jmario@redhat.com>
Acked-by: default avatarMel Gorman <mgorman@suse.de>
Reviewed-by: default avatarRik van Riel <riel@redhat.com>
Signed-off-by: default avatarPeter Zijlstra <peterz@infradead.org>
Cc: hannes@cmpxchg.org
Cc: aarcange@redhat.com
Cc: srikar@linux.vnet.ibm.com
Cc: tglx@linutronix.de
Cc: hpa@zytor.com
Link: http://lkml.kernel.org/r/20131010181722.GO13848@laptop.programming.kicks-ass.netSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
      74602315
    • Peter Zijlstra's avatar
      sched/rt: Add missing rmb() · 7c3f2ab7
      Peter Zijlstra authored 
      While discussing the proposed SCHED_DEADLINE patches which in parts
mimic the existing FIFO code it was noticed that the wmb in
rt_set_overloaded() didn't have a matching barrier.

The only site using rt_overloaded() to test the rto_count is
pull_rt_task() and we should issue a matching rmb before then assuming
there's an rto_mask bit set.

Without that smp_rmb() in there we could actually miss seeing the
rto_mask bit.

Also, change to using smp_[wr]mb(), even though this is SMP only code;
memory barriers without smp_ always make me think they're against
hardware of some sort.
Signed-off-by: default avatarPeter Zijlstra <peterz@infradead.org>
Cc: vincent.guittot@linaro.org
Cc: luca.abeni@unitn.it
Cc: bruce.ashfield@windriver.com
Cc: dhaval.giani@gmail.com
Cc: rostedt@goodmis.org
Cc: hgu1972@gmail.com
Cc: oleg@redhat.com
Cc: fweisbec@gmail.com
Cc: darren@dvhart.com
Cc: johan.eker@ericsson.com
Cc: p.faure@akatech.ch
Cc: paulmck@linux.vnet.ibm.com
Cc: raistlin@linux.it
Cc: claudio@evidence.eu.com
Cc: insop.song@gmail.com
Cc: michael@amarulasolutions.com
Cc: liming.wang@windriver.com
Cc: fchecconi@gmail.com
Cc: jkacur@redhat.com
Cc: tommaso.cucinotta@sssup.it
Cc: Juri Lelli <juri.lelli@gmail.com>
Cc: harald.gustafsson@ericsson.com
Cc: nicola.manica@disi.unitn.it
Cc: tglx@linutronix.de
Link: http://lkml.kernel.org/r/20131015103507.GF10651@twins.programming.kicks-ass.netSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
      7c3f2ab7
  3. 14 Oct, 2013 1 commit
  5. 12 Oct, 2013 1 commit
  7. 11 Oct, 2013 6 commits
  9. 10 Oct, 2013 11 commits
  11. 09 Oct, 2013 18 commits
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