sched: Fix race between ttwu() and task_rq_lock() (0970d299) · Commits · 戴 / test

kernel/sched.c

+46 −27

Original line number	Diff line number	Diff line
		@@ -940,6 +940,19 @@ static inline void finish_lock_switch(struct rq rq, struct task_struct prev)
		}
		#endif /* __ARCH_WANT_UNLOCKED_CTXSW */

		/*
		* Check whether the task is waking, we use this to synchronize against
		* ttwu() so that task_cpu() reports a stable number.
		*
		* We need to make an exception for PF_STARTING tasks because the fork
		* path might require task_rq_lock() to work, eg. it can call
		* set_cpus_allowed_ptr() from the cpuset clone_ns code.
		*/
		static inline int task_is_waking(struct task_struct *p)
		{
		return unlikely((p->state == TASK_WAKING) && !(p->flags & PF_STARTING));
		}

		/*
		* __task_rq_lock - lock the runqueue a given task resides on.
		* Must be called interrupts disabled.
		@@ -947,10 +960,14 @@ static inline void finish_lock_switch(struct rq rq, struct task_struct prev)
		static inline struct rq __task_rq_lock(struct task_struct p)
		__acquires(rq->lock)
		{
		struct rq *rq;

		for (;;) {
		struct rq *rq = task_rq(p);
		while (task_is_waking(p))
		cpu_relax();
		rq = task_rq(p);
		raw_spin_lock(&rq->lock);
		if (likely(rq == task_rq(p)))
		if (likely(rq == task_rq(p) && !task_is_waking(p)))
		return rq;
		raw_spin_unlock(&rq->lock);
		}
		@@ -967,10 +984,12 @@ static struct rq task_rq_lock(struct task_struct p, unsigned long *flags)
		struct rq *rq;

		for (;;) {
		while (task_is_waking(p))
		cpu_relax();
		local_irq_save(*flags);
		rq = task_rq(p);
		raw_spin_lock(&rq->lock);
		if (likely(rq == task_rq(p)))
		if (likely(rq == task_rq(p) && !task_is_waking(p)))
		return rq;
		raw_spin_unlock_irqrestore(&rq->lock, *flags);
		}
		@@ -2408,14 +2427,27 @@ static int try_to_wake_up(struct task_struct *p, unsigned int state,
		__task_rq_unlock(rq);

		cpu = select_task_rq(p, SD_BALANCE_WAKE, wake_flags);
		if (cpu != orig_cpu)
		if (cpu != orig_cpu) {
		/*
		* Since we migrate the task without holding any rq->lock,
		* we need to be careful with task_rq_lock(), since that
		* might end up locking an invalid rq.
		*/
		set_task_cpu(p, cpu);
		}

		rq = __task_rq_lock(p);
		rq = cpu_rq(cpu);
		raw_spin_lock(&rq->lock);
		update_rq_clock(rq);

		/*
		* We migrated the task without holding either rq->lock, however
		* since the task is not on the task list itself, nobody else
		* will try and migrate the task, hence the rq should match the
		* cpu we just moved it to.
		*/
		WARN_ON(task_cpu(p) != cpu);
		WARN_ON(p->state != TASK_WAKING);
		cpu = task_cpu(p);

		#ifdef CONFIG_SCHEDSTATS
		schedstat_inc(rq, ttwu_count);
		@@ -2647,7 +2679,7 @@ void wake_up_new_task(struct task_struct *p, unsigned long clone_flags)
		{
		unsigned long flags;
		struct rq *rq;
		int cpu __maybe_unused = get_cpu();
		int cpu = get_cpu();

		#ifdef CONFIG_SMP
		/*
		@@ -2663,7 +2695,13 @@ void wake_up_new_task(struct task_struct *p, unsigned long clone_flags)
		set_task_cpu(p, cpu);
		#endif

		rq = task_rq_lock(p, &flags);
		/*
		* Since the task is not on the rq and we still have TASK_WAKING set
		* nobody else will migrate this task.
		*/
		rq = cpu_rq(cpu);
		raw_spin_lock_irqsave(&rq->lock, flags);

		BUG_ON(p->state != TASK_WAKING);
		p->state = TASK_RUNNING;
		update_rq_clock(rq);
		@@ -7156,27 +7194,8 @@ int set_cpus_allowed_ptr(struct task_struct p, const struct cpumask new_mask)
		struct rq *rq;
		int ret = 0;

		/*
		* Since we rely on wake-ups to migrate sleeping tasks, don't change
		* the ->cpus_allowed mask from under waking tasks, which would be
		* possible when we change rq->lock in ttwu(), so synchronize against
		* TASK_WAKING to avoid that.
		*
		* Make an exception for freshly cloned tasks, since cpuset namespaces
		* might move the task about, we have to validate the target in
		* wake_up_new_task() anyway since the cpu might have gone away.
		*/
		again:
		while (p->state == TASK_WAKING && !(p->flags & PF_STARTING))
		cpu_relax();

		rq = task_rq_lock(p, &flags);

		if (p->state == TASK_WAKING && !(p->flags & PF_STARTING)) {
		task_rq_unlock(rq, &flags);
		goto again;
		}

		if (!cpumask_intersects(new_mask, cpu_active_mask)) {
		ret = -EINVAL;
		goto out;

Admin message