Commit 90450a06 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge tag 'rcu-fixes-v6.7' of git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks 

Pull RCU fixes from Frederic Weisbecker:

 - Fix a lock inversion between scheduler and RCU introduced in
   v6.2-rc4. The scenario could trigger on any user of RCU_NOCB
   (mostly Android but also nohz_full)

 - Fix PF_IDLE semantic changes introduced in v6.6-rc3 breaking
   some RCU-Tasks and RCU-Tasks-Trace expectations as to what
   exactly is an idle task. This resulted in potential spurious
   stalls and warnings.

* tag 'rcu-fixes-v6.7' of git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks:
  rcu/tasks-trace: Handle new PF_IDLE semantics
  rcu/tasks: Handle new PF_IDLE semantics
  rcu: Introduce rcu_cpu_online()
  rcu: Break rcu_node_0 --> &rq->__lock order
parents 447cec03 a80712b9

kernel/rcu/rcu.h

+2 −0
Original line number Diff line number Diff line
@@ -500,6 +500,7 @@ static inline void rcu_expedite_gp(void) { } 
static inline void rcu_unexpedite_gp(void) { }

static inline void rcu_async_hurry(void) { }

static inline void rcu_async_relax(void) { }

static inline bool rcu_cpu_online(int cpu) { return true; }

#else /* #ifdef CONFIG_TINY_RCU */

bool rcu_gp_is_normal(void);     /* Internal RCU use. */

bool rcu_gp_is_expedited(void);  /* Internal RCU use. */
@@ -509,6 +510,7 @@ void rcu_unexpedite_gp(void); 
void rcu_async_hurry(void);

void rcu_async_relax(void);

void rcupdate_announce_bootup_oddness(void);

bool rcu_cpu_online(int cpu);

#ifdef CONFIG_TASKS_RCU_GENERIC

void show_rcu_tasks_gp_kthreads(void);

#else /* #ifdef CONFIG_TASKS_RCU_GENERIC */

kernel/rcu/tasks.h

+29 −3
Original line number Diff line number Diff line
@@ -895,10 +895,36 @@ static void rcu_tasks_pregp_step(struct list_head *hop) 
	synchronize_rcu();

}



/* Check for quiescent states since the pregp's synchronize_rcu() */

static bool rcu_tasks_is_holdout(struct task_struct *t)

{

	int cpu;



	/* Has the task been seen voluntarily sleeping? */

	if (!READ_ONCE(t->on_rq))

		return false;



	/*

	 * Idle tasks (or idle injection) within the idle loop are RCU-tasks

	 * quiescent states. But CPU boot code performed by the idle task

	 * isn't a quiescent state.

	 */

	if (is_idle_task(t))

		return false;



	cpu = task_cpu(t);



	/* Idle tasks on offline CPUs are RCU-tasks quiescent states. */

	if (t == idle_task(cpu) && !rcu_cpu_online(cpu))

		return false;



	return true;

}



/* Per-task initial processing. */

static void rcu_tasks_pertask(struct task_struct *t, struct list_head *hop)

{

	if (t != current && READ_ONCE(t->on_rq) && !is_idle_task(t)) {

	if (t != current && rcu_tasks_is_holdout(t)) {

		get_task_struct(t);

		t->rcu_tasks_nvcsw = READ_ONCE(t->nvcsw);

		WRITE_ONCE(t->rcu_tasks_holdout, true);
@@ -947,7 +973,7 @@ static void check_holdout_task(struct task_struct *t, 


	if (!READ_ONCE(t->rcu_tasks_holdout) ||

	    t->rcu_tasks_nvcsw != READ_ONCE(t->nvcsw) ||

	    !READ_ONCE(t->on_rq) ||

	    !rcu_tasks_is_holdout(t) ||

	    (IS_ENABLED(CONFIG_NO_HZ_FULL) &&

	     !is_idle_task(t) && t->rcu_tasks_idle_cpu >= 0)) {

		WRITE_ONCE(t->rcu_tasks_holdout, false);
@@ -1525,7 +1551,7 @@ static int trc_inspect_reader(struct task_struct *t, void *bhp_in) 
	} else {

		// The task is not running, so C-language access is safe.

		nesting = t->trc_reader_nesting;

		WARN_ON_ONCE(ofl && task_curr(t) && !is_idle_task(t));

		WARN_ON_ONCE(ofl && task_curr(t) && (t != idle_task(task_cpu(t))));

		if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB) && ofl)

			n_heavy_reader_ofl_updates++;

	}

kernel/rcu/tree.c

+32 −11
Original line number Diff line number Diff line
@@ -755,14 +755,19 @@ static int dyntick_save_progress_counter(struct rcu_data *rdp) 
}



/*

 * Return true if the specified CPU has passed through a quiescent

 * state by virtue of being in or having passed through an dynticks

 * idle state since the last call to dyntick_save_progress_counter()

 * for this same CPU, or by virtue of having been offline.

 * Returns positive if the specified CPU has passed through a quiescent state

 * by virtue of being in or having passed through an dynticks idle state since

 * the last call to dyntick_save_progress_counter() for this same CPU, or by

 * virtue of having been offline.

 *

 * Returns negative if the specified CPU needs a force resched.

 *

 * Returns zero otherwise.

 */

static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)

{

	unsigned long jtsq;

	int ret = 0;

	struct rcu_node *rnp = rdp->mynode;



	/*
@@ -848,8 +853,8 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) 
	    (time_after(jiffies, READ_ONCE(rdp->last_fqs_resched) + jtsq * 3) ||

	     rcu_state.cbovld)) {

		WRITE_ONCE(rdp->rcu_urgent_qs, true);

		resched_cpu(rdp->cpu);

		WRITE_ONCE(rdp->last_fqs_resched, jiffies);

		ret = -1;

	}



	/*
@@ -862,8 +867,8 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) 
	if (time_after(jiffies, rcu_state.jiffies_resched)) {

		if (time_after(jiffies,

			       READ_ONCE(rdp->last_fqs_resched) + jtsq)) {

			resched_cpu(rdp->cpu);

			WRITE_ONCE(rdp->last_fqs_resched, jiffies);

			ret = -1;

		}

		if (IS_ENABLED(CONFIG_IRQ_WORK) &&

		    !rdp->rcu_iw_pending && rdp->rcu_iw_gp_seq != rnp->gp_seq &&
@@ -892,7 +897,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) 
		}

	}



	return 0;

	return ret;

}



/* Trace-event wrapper function for trace_rcu_future_grace_period.  */
@@ -2271,15 +2276,15 @@ static void force_qs_rnp(int (*f)(struct rcu_data *rdp)) 
{

	int cpu;

	unsigned long flags;

	unsigned long mask;

	struct rcu_data *rdp;

	struct rcu_node *rnp;



	rcu_state.cbovld = rcu_state.cbovldnext;

	rcu_state.cbovldnext = false;

	rcu_for_each_leaf_node(rnp) {

		unsigned long mask = 0;

		unsigned long rsmask = 0;



		cond_resched_tasks_rcu_qs();

		mask = 0;

		raw_spin_lock_irqsave_rcu_node(rnp, flags);

		rcu_state.cbovldnext |= !!rnp->cbovldmask;

		if (rnp->qsmask == 0) {
@@ -2297,11 +2302,17 @@ static void force_qs_rnp(int (*f)(struct rcu_data *rdp)) 
			continue;

		}

		for_each_leaf_node_cpu_mask(rnp, cpu, rnp->qsmask) {

			struct rcu_data *rdp;

			int ret;



			rdp = per_cpu_ptr(&rcu_data, cpu);

			if (f(rdp)) {

			ret = f(rdp);

			if (ret > 0) {

				mask |= rdp->grpmask;

				rcu_disable_urgency_upon_qs(rdp);

			}

			if (ret < 0)

				rsmask |= rdp->grpmask;

		}

		if (mask != 0) {

			/* Idle/offline CPUs, report (releases rnp->lock). */
@@ -2310,6 +2321,9 @@ static void force_qs_rnp(int (*f)(struct rcu_data *rdp)) 
			/* Nothing to do here, so just drop the lock. */

			raw_spin_unlock_irqrestore_rcu_node(rnp, flags);

		}



		for_each_leaf_node_cpu_mask(rnp, cpu, rsmask)

			resched_cpu(cpu);

	}

}
@@ -4195,6 +4209,13 @@ static bool rcu_rdp_cpu_online(struct rcu_data *rdp) 
	return !!(rdp->grpmask & rcu_rnp_online_cpus(rdp->mynode));

}



bool rcu_cpu_online(int cpu)

{

	struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);



	return rcu_rdp_cpu_online(rdp);

}



#if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)



/*