linux-stable.git/kernel/sched_rt.c, branch linux-2.6.34.y

sched/rt: Fix task stack corruption under __ARCH_WANT_INTERRUPTS_ON_CTXSW

2013-01-16T21:45:08+00:00

commit cb297a3e433dbdcf7ad81e0564e7b804c941ff0d upstream.

This issue happens under the following conditions:

 1. preemption is off
 2. __ARCH_WANT_INTERRUPTS_ON_CTXSW is defined
 3. RT scheduling class
 4. SMP system

Sequence is as follows:

 1.suppose current task is A. start schedule()
 2.task A is enqueued pushable task at the entry of schedule()
   __schedule
    prev = rq->curr;
    ...
    put_prev_task
     put_prev_task_rt
      enqueue_pushable_task
 4.pick the task B as next task.
   next = pick_next_task(rq);
 3.rq->curr set to task B and context_switch is started.
   rq->curr = next;
 4.At the entry of context_swtich, release this cpu's rq->lock.
   context_switch
    prepare_task_switch
     prepare_lock_switch
      raw_spin_unlock_irq(&rq->lock);
 5.Shortly after rq->lock is released, interrupt is occurred and start IRQ context
 6.try_to_wake_up() which called by ISR acquires rq->lock
    try_to_wake_up
     ttwu_remote
      rq = __task_rq_lock(p)
      ttwu_do_wakeup(rq, p, wake_flags);
        task_woken_rt
 7.push_rt_task picks the task A which is enqueued before.
   task_woken_rt
    push_rt_tasks(rq)
     next_task = pick_next_pushable_task(rq)
 8.At find_lock_lowest_rq(), If double_lock_balance() returns 0,
   lowest_rq can be the remote rq.
  (But,If preemption is on, double_lock_balance always return 1 and it
   does't happen.)
   push_rt_task
    find_lock_lowest_rq
     if (double_lock_balance(rq, lowest_rq))..
 9.find_lock_lowest_rq return the available rq. task A is migrated to
   the remote cpu/rq.
   push_rt_task
    ...
    deactivate_task(rq, next_task, 0);
    set_task_cpu(next_task, lowest_rq->cpu);
    activate_task(lowest_rq, next_task, 0);
 10. But, task A is on irq context at this cpu.
     So, task A is scheduled by two cpus at the same time until restore from IRQ.
     Task A's stack is corrupted.

To fix it, don't migrate an RT task if it's still running.

Signed-off-by: Chanho Min 
Signed-off-by: Peter Zijlstra 
Acked-by: Steven Rostedt 
Link: http://lkml.kernel.org/r/CAOAMb1BHA=5fm7KTewYyke6u-8DP0iUuJMpgQw54vNeXFsGpoQ@mail.gmail.com
Signed-off-by: Ingo Molnar 
[PG: in 2.6.34, sched/rt.c is just sched_rt.c]
Signed-off-by: Paul Gortmaker

sched: Fix TASK_WAKING vs fork deadlock

2011-01-06T23:07:51+00:00

commit 0017d735092844118bef006696a750a0e4ef6ebd upstream.

Oleg noticed a few races with the TASK_WAKING usage on fork.

 - since TASK_WAKING is basically a spinlock, it should be IRQ safe
 - since we set TASK_WAKING (*) without holding rq->lock it could
   be there still is a rq->lock holder, thereby not actually
   providing full serialization.

(*) in fact we clear PF_STARTING, which in effect enables TASK_WAKING.

Cure the second issue by not setting TASK_WAKING in sched_fork(), but
only temporarily in wake_up_new_task() while calling select_task_rq().

Cure the first by holding rq->lock around the select_task_rq() call,
this will disable IRQs, this however requires that we push down the
rq->lock release into select_task_rq_fair()'s cgroup stuff.

Because select_task_rq_fair() still needs to drop the rq->lock we
cannot fully get rid of TASK_WAKING.

Reported-by: Oleg Nesterov 
Signed-off-by: Peter Zijlstra 
LKML-Reference: 
Signed-off-by: Ingo Molnar 
Signed-off-by: Paul Gortmaker

Merge branch 'sched-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip

2010-03-13T22:46:18+00:00

* 'sched-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  sched: Fix pick_next_highest_task_rt() for cgroups
  sched: Cleanup: remove unused variable in try_to_wake_up()
  x86: Fix sched_clock_cpu for systems with unsynchronized TSC

sched: Fix pick_next_highest_task_rt() for cgroups

2010-03-11T14:21:50+00:00

Since pick_next_highest_task_rt() already iterates all the cgroups and
is really only interested in tasks, skip over the !task entries.

Reported-by: Dhaval Giani 
Signed-off-by: Peter Zijlstra 
Tested-by: Dhaval Giani 
LKML-Reference: 
Signed-off-by: Ingo Molnar

kernel core: use helpers for rlimits

2010-03-06T19:26:33+00:00

Make sure compiler won't do weird things with limits.  E.g.  fetching them
twice may return 2 different values after writable limits are implemented.

I.e.  either use rlimit helpers added in commit 3e10e716abf3 ("resource:
add helpers for fetching rlimits") or ACCESS_ONCE if not applicable.

Signed-off-by: Jiri Slaby 
Cc: Ingo Molnar 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: john stultz 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

sched: Change usage of rt_rq->rt_se to rt_rq->tg->rt_se[cpu]

2010-02-04T08:57:32+00:00

This is the first step to remove rt_rq member rt_se because it have the
same meaning with tg->rt_se[cpu]. And the latter style is also used by
the fair scheduling class.

Signed-off-by: Yong Zhang 
Cc: Rusty Russell 
Signed-off-by: Peter Zijlstra 
LKML-Reference: <2674af741001282257r28c97a92o9f90cf16fe8d3d84@mail.gmail.com>
Signed-off-by: Ingo Molnar

sched: Implement head queueing for sched_rt

2010-01-22T17:09:59+00:00

The ability of enqueueing a task to the head of a SCHED_FIFO priority
list is required to fix some violations of POSIX scheduling policy.

Implement the functionality in sched_rt.

Signed-off-by: Thomas Gleixner 
Acked-by: Peter Zijlstra 
Tested-by: Carsten Emde 
Tested-by: Mathias Weber 
LKML-Reference: <20100120171629.772169931@linutronix.de>

sched: Extend enqueue_task to allow head queueing

2010-01-22T17:09:59+00:00

The ability of enqueueing a task to the head of a SCHED_FIFO priority
list is required to fix some violations of POSIX scheduling policy.

Extend the related functions with a "head" argument.

Signed-off-by: Thomas Gleixner 
Acked-by: Peter Zijlstra 
Tested-by: Carsten Emde 
Tested-by: Mathias Weber 
LKML-Reference: <20100120171629.734886007@linutronix.de>

sched: Remove the sched_class load_balance methods

2010-01-21T12:40:09+00:00

Take out the sched_class methods for load-balancing.

Signed-off-by: Peter Zijlstra 
LKML-Reference: 
Signed-off-by: Ingo Molnar

sched: Don't expose local functions

2010-01-17T07:09:45+00:00

kernel/sched: don't expose local functions

The get_rr_interval_* functions are all class methods of
struct sched_class. They are not exported so make them
static.

Signed-off-by: H Hartley Sweeten 
Cc: Peter Zijlstra 
LKML-Reference: <201001132021.53253.hartleys@visionengravers.com>
Signed-off-by: Ingo Molnar