linux-toradex.git/kernel/sched_fair.c, branch v3.2.73

sched: Fix double normalization of vruntime

2014-04-01T23:58:56+00:00

commit 791c9e0292671a3bfa95286bb5c08129d8605618 upstream.

dequeue_entity() is called when p->on_rq and sets se->on_rq = 0
which appears to guarentee that the !se->on_rq condition is met.
If the task has done set_current_state(TASK_INTERRUPTIBLE) without
schedule() the second condition will be met and vruntime will be
incorrectly adjusted twice.

In certain cases this can result in the task's vruntime never increasing
past the vruntime of other tasks on the CFS' run queue, starving them of
CPU time.

This patch changes switched_from_fair() to use !p->on_rq instead of
!se->on_rq.

I'm able to cause a task with a priority of 120 to starve all other
tasks with the same priority on an ARM platform running 3.2.51-rt72
PREEMPT RT by writing one character at time to a serial tty (16550 UART)
in a tight loop. I'm also able to verify making this change corrects the
problem on that platform and kernel version.

Signed-off-by: George McCollister 
Signed-off-by: Peter Zijlstra 
Link: http://lkml.kernel.org/r/1392767811-28916-1-git-send-email-george.mccollister@gmail.com
Signed-off-by: Ingo Molnar 
[bwh: Backported to 3.2: adjust filename]
Signed-off-by: Ben Hutchings

sched: Unthrottle rt runqueues in __disable_runtime()

2014-02-15T19:20:18+00:00

commit a4c96ae319b8047f62dedbe1eac79e321c185749 upstream.

migrate_tasks() uses _pick_next_task_rt() to get tasks from the
real-time runqueues to be migrated. When rt_rq is throttled
_pick_next_task_rt() won't return anything, in which case
migrate_tasks() can't move all threads over and gets stuck in an
infinite loop.

Instead unthrottle rt runqueues before migrating tasks.

Additionally: move unthrottle_offline_cfs_rqs() to rq_offline_fair()

Signed-off-by: Peter Boonstoppel 
Signed-off-by: Peter Zijlstra 
Cc: Paul Turner 
Link: http://lkml.kernel.org/r/5FBF8E85CA34454794F0F7ECBA79798F379D3648B7@HQMAIL04.nvidia.com
Signed-off-by: Ingo Molnar 
[ lizf: backported to 3.4: adjust context ]
Signed-off-by: Li Zefan 
[bwh: Backported to 3.2:
 - Adjust filenames
 - unthrottle_offline_cfs_rqs() is already static, but defined in sched.c
   after including sched_fair.c, so add forward declaration
 - unthrottle_offline_cfs_rqs() also needs to be defined for all CONFIG_SMP
   configurations now]
Signed-off-by: Ben Hutchings

sched: Avoid throttle_cfs_rq() racing with period_timer stopping

2014-01-03T04:33:31+00:00

commit f9f9ffc237dd924f048204e8799da74f9ecf40cf upstream.

throttle_cfs_rq() doesn't check to make sure that period_timer is running,
and while update_curr/assign_cfs_runtime does, a concurrently running
period_timer on another cpu could cancel itself between this cpu's
update_curr and throttle_cfs_rq(). If there are no other cfs_rqs running
in the tg to restart the timer, this causes the cfs_rq to be stranded
forever.

Fix this by calling __start_cfs_bandwidth() in throttle if the timer is
inactive.

(Also add some sched_debug lines for cfs_bandwidth.)

Tested: make a run/sleep task in a cgroup, loop switching the cgroup
between 1ms/100ms quota and unlimited, checking for timer_active=0 and
throttled=1 as a failure. With the throttle_cfs_rq() change commented out
this fails, with the full patch it passes.

Signed-off-by: Ben Segall 
Signed-off-by: Peter Zijlstra 
Cc: pjt@google.com
Link: http://lkml.kernel.org/r/20131016181632.22647.84174.stgit@sword-of-the-dawn.mtv.corp.google.com
Signed-off-by: Ingo Molnar 
[bwh: Backported to 3.2: adjust filenames]
Signed-off-by: Ben Hutchings

sched/fair: Fix small race where child->se.parent,cfs_rq might point to invalid ones

2013-10-26T20:06:03+00:00

commit 6c9a27f5da9609fca46cb2b183724531b48f71ad upstream.

There is a small race between copy_process() and cgroup_attach_task()
where child->se.parent,cfs_rq points to invalid (old) ones.

        parent doing fork()      | someone moving the parent to another cgroup
  -------------------------------+---------------------------------------------
    copy_process()
      + dup_task_struct()
        -> parent->se is copied to child->se.
           se.parent,cfs_rq of them point to old ones.

                                     cgroup_attach_task()
                                       + cgroup_task_migrate()
                                         -> parent->cgroup is updated.
                                       + cpu_cgroup_attach()
                                         + sched_move_task()
                                           + task_move_group_fair()
                                             +- set_task_rq()
                                                -> se.parent,cfs_rq of parent
                                                   are updated.

      + cgroup_fork()
        -> parent->cgroup is copied to child->cgroup. (*1)
      + sched_fork()
        + task_fork_fair()
          -> se.parent,cfs_rq of child are accessed
             while they point to old ones. (*2)

In the worst case, this bug can lead to "use-after-free" and cause a panic,
because it's new cgroup's refcount that is incremented at (*1),
so the old cgroup(and related data) can be freed before (*2).

In fact, a panic caused by this bug was originally caught in RHEL6.4.

    BUG: unable to handle kernel NULL pointer dereference at (null)
    IP: [] sched_slice+0x6e/0xa0
    [...]
    Call Trace:
     [] place_entity+0x75/0xa0
     [] task_fork_fair+0xaa/0x160
     [] sched_fork+0x6b/0x140
     [] copy_process+0x5b2/0x1450
     [] ? wake_up_new_task+0xd9/0x130
     [] do_fork+0x94/0x460
     [] ? sys_wait4+0xae/0x100
     [] sys_clone+0x28/0x30
     [] stub_clone+0x13/0x20
     [] ? system_call_fastpath+0x16/0x1b

Signed-off-by: Daisuke Nishimura 
Signed-off-by: Peter Zijlstra 
Link: http://lkml.kernel.org/r/039601ceae06$733d3130$59b79390$@mxp.nes.nec.co.jp
Signed-off-by: Ingo Molnar 
[bwh: Backported to 3.2: adjust filename]
Signed-off-by: Ben Hutchings

sched: Fix the broken sched_rr_get_interval()

2013-09-10T00:57:04+00:00

commit a59f4e079d19464eebb9b06513a1d4f55fdae5ba upstream.

The caller of sched_sliced() should pass se.cfs_rq and se as the
arguments, however in sched_rr_get_interval() we gave it
rq.cfs_rq and se, which made the following computation obviously
wrong.

The change was introduced by commit:

  77034937dc45 sched: fix crash in sys_sched_rr_get_interval()

... 5 years ago, while it had been the correct 'cfs_rq_of' before
the commit. The change seems to be irrelevant to the commit
msg, which was to return a 0 timeslice for tasks that are on an
idle runqueue. So I believe that was just a plain typo.

Signed-off-by: Zhu Yanhai 
Cc: Peter Zijlstra 
Cc: Paul Turner 
Cc: Thomas Gleixner 
Cc: Steven Rostedt 
Cc: Andrew Morton 
Cc: Linus Torvalds 
Link: http://lkml.kernel.org/r/1357621012-15039-1-git-send-email-gaoyang.zyh@taobao.com
[ Since this is an ABI and an old bug, we'll test this via a
  slow upstream route, to hopefully discover any app breakage. ]
Signed-off-by: Ingo Molnar 
Signed-off-by: Ben Hutchings

sched/nohz: Fix rq->cpu_load[] calculations

2012-08-02T13:37:38+00:00

commit 556061b00c9f2fd6a5524b6bde823ef12f299ecf upstream.

While investigating why the load-balancer did funny I found that the
rq->cpu_load[] tables were completely screwy.. a bit more digging
revealed that the updates that got through were missing ticks followed
by a catchup of 2 ticks.

The catchup assumes the cpu was idle during that time (since only nohz
can cause missed ticks and the machine is idle etc..) this means that
esp. the higher indices were significantly lower than they ought to
be.

The reason for this is that its not correct to compare against jiffies
on every jiffy on any other cpu than the cpu that updates jiffies.

This patch cludges around it by only doing the catch-up stuff from
nohz_idle_balance() and doing the regular stuff unconditionally from
the tick.

Signed-off-by: Peter Zijlstra 
Cc: pjt@google.com
Cc: Venkatesh Pallipadi 
Link: http://lkml.kernel.org/n/tip-tp4kj18xdd5aj4vvj0qg55s2@git.kernel.org
Signed-off-by: Ingo Molnar 
[bwh: Backported to 3.2: adjust filenames and context; keep functions static]
Signed-off-by: Ben Hutchings

sched: Fix select_idle_sibling() regression in selecting an idle SMT sibling

2011-12-16T08:44:58+00:00

Mike Galbraith reported that this recent commit:

   commit 4dcfe1025b513c2c1da5bf5586adb0e80148f612
   Author: Peter Zijlstra 
   Date:   Thu Nov 10 13:01:10 2011 +0100

       sched: Avoid SMT siblings in select_idle_sibling() if possible

stopped selecting an idle SMT sibling when there are no idle
cores in a single socket system.

Intent of the select_idle_sibling() was to fallback to an idle
SMT sibling, if it fails to identify an idle core. But this
fallback was not happening on systems where all the scheduler
domains had `SD_SHARE_PKG_RESOURCES' flag set.

Fix it. Slightly bigger patch of cleaning all these goto's etc
is queued up for the next release.

Reported-by: Mike Galbraith 
Reported-by: Alex Shi 
Signed-off-by: Peter Zijlstra 
Signed-off-by: Suresh Siddha 
Link: http://lkml.kernel.org/r/1323978421.1984.244.camel@sbsiddha-desk.sc.intel.com
Signed-off-by: Ingo Molnar

sched: Fix buglet in return_cfs_rq_runtime()

2011-11-16T07:43:45+00:00

In return_cfs_rq_runtime() we want to return bandwidth when there are no
remaining tasks, not "return" when this is the case.

Signed-off-by: Paul Turner 
Signed-off-by: Peter Zijlstra 
Link: http://lkml.kernel.org/r/20111108042736.623812423@google.com
Signed-off-by: Ingo Molnar

sched: Avoid SMT siblings in select_idle_sibling() if possible

2011-11-16T07:43:43+00:00

Avoid select_idle_sibling() from picking a sibling thread if there's
an idle core that shares cache.

This fixes SMT balancing in the increasingly common case where there's
a shared cache core available to balance to.

Tested-by: Mike Galbraith 
Signed-off-by: Peter Zijlstra 
Cc: Suresh Siddha 
Link: http://lkml.kernel.org/r/1321350377.1421.55.camel@twins
Signed-off-by: Ingo Molnar

sched_fair: Fix a typo in the comment describing update_sd_lb_stats

2011-11-14T11:50:34+00:00

Signed-off-by: Hui Kang 
Signed-off-by: Peter Zijlstra 
Link: http://lkml.kernel.org/r/1318388459-4427-1-git-send-email-hkang.sunysb@gmail.com
Signed-off-by: Ingo Molnar