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authorHiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>2008-03-10 11:01:20 -0700
committerIngo Molnar <mingo@elte.hu>2008-03-15 03:02:49 +0100
commit0e1f34833bd9170ccc93ab759e48e695917fa48f (patch)
tree2ca4b89dd755f2d82dbd34466a8cd6d8b5b4a0af
parent4faa8496650f9417189dacce8f933e8ec61dc032 (diff)
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sched: fix race in schedule()
Fix a hard to trigger crash seen in the -rt kernel that also affects the vanilla scheduler. There is a race condition between schedule() and some dequeue/enqueue functions; rt_mutex_setprio(), __setscheduler() and sched_move_task(). When scheduling to idle, idle_balance() is called to pull tasks from other busy processor. It might drop the rq lock. It means that those 3 functions encounter on_rq=0 and running=1. The current task should be put when running. Here is a possible scenario: CPU0 CPU1 | schedule() | ->deactivate_task() | ->idle_balance() | -->load_balance_newidle() rt_mutex_setprio() | | --->double_lock_balance() *get lock *rel lock * on_rq=0, ruuning=1 | * sched_class is changed | *rel lock *get lock : | : ->put_prev_task_rt() ->pick_next_task_fair() => panic The current process of CPU1(P1) is scheduling. Deactivated P1, and the scheduler looks for another process on other CPU's runqueue because CPU1 will be idle. idle_balance(), load_balance_newidle() and double_lock_balance() are called and double_lock_balance() could drop the rq lock. On the other hand, CPU0 is trying to boost the priority of P1. The result of boosting only P1's prio and sched_class are changed to RT. The sched entities of P1 and P1's group are never put. It makes cfs_rq invalid, because the cfs_rq has curr and no leaf, but pick_next_task_fair() is called, then the kernel panics. Signed-off-by: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: Ingo Molnar <mingo@elte.hu>
-rw-r--r--kernel/sched.c38
1 files changed, 16 insertions, 22 deletions
diff --git a/kernel/sched.c b/kernel/sched.c
index 1cb53fb1fe3..9df9ba73cb7 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -4268,11 +4268,10 @@ void rt_mutex_setprio(struct task_struct *p, int prio)
oldprio = p->prio;
on_rq = p->se.on_rq;
running = task_current(rq, p);
- if (on_rq) {
+ if (on_rq)
dequeue_task(rq, p, 0);
- if (running)
- p->sched_class->put_prev_task(rq, p);
- }
+ if (running)
+ p->sched_class->put_prev_task(rq, p);
if (rt_prio(prio))
p->sched_class = &rt_sched_class;
@@ -4281,10 +4280,9 @@ void rt_mutex_setprio(struct task_struct *p, int prio)
p->prio = prio;
+ if (running)
+ p->sched_class->set_curr_task(rq);
if (on_rq) {
- if (running)
- p->sched_class->set_curr_task(rq);
-
enqueue_task(rq, p, 0);
check_class_changed(rq, p, prev_class, oldprio, running);
@@ -4581,19 +4579,17 @@ recheck:
update_rq_clock(rq);
on_rq = p->se.on_rq;
running = task_current(rq, p);
- if (on_rq) {
+ if (on_rq)
deactivate_task(rq, p, 0);
- if (running)
- p->sched_class->put_prev_task(rq, p);
- }
+ if (running)
+ p->sched_class->put_prev_task(rq, p);
oldprio = p->prio;
__setscheduler(rq, p, policy, param->sched_priority);
+ if (running)
+ p->sched_class->set_curr_task(rq);
if (on_rq) {
- if (running)
- p->sched_class->set_curr_task(rq);
-
activate_task(rq, p, 0);
check_class_changed(rq, p, prev_class, oldprio, running);
@@ -7618,11 +7614,10 @@ void sched_move_task(struct task_struct *tsk)
running = task_current(rq, tsk);
on_rq = tsk->se.on_rq;
- if (on_rq) {
+ if (on_rq)
dequeue_task(rq, tsk, 0);
- if (unlikely(running))
- tsk->sched_class->put_prev_task(rq, tsk);
- }
+ if (unlikely(running))
+ tsk->sched_class->put_prev_task(rq, tsk);
set_task_rq(tsk, task_cpu(tsk));
@@ -7631,11 +7626,10 @@ void sched_move_task(struct task_struct *tsk)
tsk->sched_class->moved_group(tsk);
#endif
- if (on_rq) {
- if (unlikely(running))
- tsk->sched_class->set_curr_task(rq);
+ if (unlikely(running))
+ tsk->sched_class->set_curr_task(rq);
+ if (on_rq)
enqueue_task(rq, tsk, 0);
- }
task_rq_unlock(rq, &flags);
}