Messages in this thread Patch in this message |  | | From | Paul Gortmaker <> | Subject | [v2.6.34-stable 73/77] sched/rt: Fix task stack corruption under __ARCH_WANT_INTERRUPTS_ON_CTXSW | Date | Tue, 8 Jan 2013 18:35:52 -0500 |
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From: Chanho Min <chanho0207@gmail.com>
------------------- This is a commit scheduled for the next v2.6.34 longterm release. http://git.kernel.org/?p=linux/kernel/git/paulg/longterm-queue-2.6.34.git If you see a problem with using this for longterm, please comment. -------------------
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 <chanho.min@lge.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Acked-by: Steven Rostedt <rostedt@goodmis.org> Link: http://lkml.kernel.org/r/CAOAMb1BHA=5fm7KTewYyke6u-8DP0iUuJMpgQw54vNeXFsGpoQ@mail.gmail.com Signed-off-by: Ingo Molnar <mingo@elte.hu> [PG: in 2.6.34, sched/rt.c is just sched_rt.c] Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com> --- kernel/sched_rt.c | 5 +++++ 1 file changed, 5 insertions(+)
diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c index fd8c1a3..abd5cba 100644 --- a/kernel/sched_rt.c +++ b/kernel/sched_rt.c @@ -1315,6 +1315,11 @@ static int push_rt_task(struct rq *rq) if (!next_task) return 0; +#ifdef __ARCH_WANT_INTERRUPTS_ON_CTXSW + if (unlikely(task_running(rq, next_task))) + return 0; +#endif + retry: if (unlikely(next_task == rq->curr)) { WARN_ON(1); -- 1.7.12.1
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