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authorOleg Nesterov <oleg@redhat.com>2010-03-15 10:10:10 +0100
committerIngo Molnar <mingo@elte.hu>2010-04-02 20:12:01 +0200
commit1445c08d06c5594895b4fae952ef8a457e89c390 (patch)
treee6fe92454d978ec8b7b84511661c7c5965307bf8 /kernel/sched.c
parent897f0b3c3ff40b443c84e271bef19bd6ae885195 (diff)
sched: move_task_off_dead_cpu(): Take rq->lock around select_fallback_rq()
move_task_off_dead_cpu()->select_fallback_rq() reads/updates ->cpus_allowed lockless. We can race with set_cpus_allowed() running in parallel. Change it to take rq->lock around select_fallback_rq(). Note that it is not trivial to move this spin_lock() into select_fallback_rq(), we must recheck the task was not migrated after we take the lock and other callers do not need this lock. To avoid the races with other callers of select_fallback_rq() which rely on TASK_WAKING, we also check p->state != TASK_WAKING and do nothing otherwise. The owner of TASK_WAKING must update ->cpus_allowed and choose the correct CPU anyway, and the subsequent __migrate_task() is just meaningless because p->se.on_rq must be false. Alternatively, we could change select_task_rq() to take rq->lock right after it calls sched_class->select_task_rq(), but this looks a bit ugly. Also, change it to not assume irqs are disabled and absorb __migrate_task_irq(). Signed-off-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <20100315091010.GA9131@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/sched.c')
-rw-r--r--kernel/sched.c30
1 files changed, 15 insertions, 15 deletions
diff --git a/kernel/sched.c b/kernel/sched.c
index c0b3ebc16317..27774b5aeb61 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -5448,29 +5448,29 @@ static int migration_thread(void *data)
}
#ifdef CONFIG_HOTPLUG_CPU
-
-static int __migrate_task_irq(struct task_struct *p, int src_cpu, int dest_cpu)
-{
- int ret;
-
- local_irq_disable();
- ret = __migrate_task(p, src_cpu, dest_cpu);
- local_irq_enable();
- return ret;
-}
-
/*
* Figure out where task on dead CPU should go, use force if necessary.
*/
static void move_task_off_dead_cpu(int dead_cpu, struct task_struct *p)
{
- int dest_cpu;
-
+ struct rq *rq = cpu_rq(dead_cpu);
+ int needs_cpu, uninitialized_var(dest_cpu);
+ unsigned long flags;
again:
- dest_cpu = select_fallback_rq(dead_cpu, p);
+ local_irq_save(flags);
+
+ raw_spin_lock(&rq->lock);
+ needs_cpu = (task_cpu(p) == dead_cpu) && (p->state != TASK_WAKING);
+ if (needs_cpu)
+ dest_cpu = select_fallback_rq(dead_cpu, p);
+ raw_spin_unlock(&rq->lock);
/* It can have affinity changed while we were choosing. */
- if (unlikely(!__migrate_task_irq(p, dead_cpu, dest_cpu)))
+ if (needs_cpu)
+ needs_cpu = !__migrate_task(p, dead_cpu, dest_cpu);
+ local_irq_restore(flags);
+
+ if (unlikely(needs_cpu))
goto again;
}