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Subject[PATCH] sched: fix priority leakage in pick_next_highest_task_rt()
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When picking the second highest RT task for a given runqueue, if no
task found after scanning the queue of priority == idx, the next idx
should also be checked even in case that next is already existing, or
the window of priority leakage could be opened.

Signed-off-by: Hillf Danton <dhillf@gmail.com>
---

--- a/kernel/sched_rt.c 2011-04-27 11:48:50.000000000 +0800
+++ b/kernel/sched_rt.c 2011-05-16 19:58:42.000000000 +0800
@@ -1166,6 +1166,8 @@ static struct task_struct *pick_next_hig
int idx;

for_each_leaf_rt_rq(rt_rq, rq) {
+ struct task_struct *this;
+
array = &rt_rq->active;
idx = sched_find_first_bit(array->bitmap);
next_idx:
@@ -1173,6 +1175,7 @@ next_idx:
continue;
if (next && next->prio < idx)
continue;
+ this = NULL;
list_for_each_entry(rt_se, array->queue + idx, run_list) {
struct task_struct *p;

@@ -1181,11 +1184,15 @@ next_idx:

p = rt_task_of(rt_se);
if (pick_rt_task(rq, p, cpu)) {
- next = p;
+ this = p;
break;
}
}
- if (!next) {
+ if (this != NULL)
+ next = this;
+ else { /*
+ * we have to check next idx even if next != NULL
+ */
idx = find_next_bit(array->bitmap, MAX_RT_PRIO, idx+1);
goto next_idx;
}

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