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Subject[tip:sched/core] sched/rt: Fix task stack corruption under __ARCH_WANT_INTERRUPTS_ON_CTXSW
Commit-ID:  cb297a3e433dbdcf7ad81e0564e7b804c941ff0d
Gitweb: http://git.kernel.org/tip/cb297a3e433dbdcf7ad81e0564e7b804c941ff0d
Author: Chanho Min <chanho0207@gmail.com>
AuthorDate: Thu, 5 Jan 2012 20:00:19 +0900
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Fri, 27 Jan 2012 12:49:41 +0100

sched/rt: Fix task stack corruption under __ARCH_WANT_INTERRUPTS_ON_CTXSW

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>
Cc: <stable@kernel.org>
Link: http://lkml.kernel.org/r/CAOAMb1BHA=5fm7KTewYyke6u-8DP0iUuJMpgQw54vNeXFsGpoQ@mail.gmail.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
kernel/sched/rt.c | 5 +++++
1 files changed, 5 insertions(+), 0 deletions(-)
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 3640ebb..f42ae7f 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1587,6 +1587,11 @@ 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);

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