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Commit 4bc8d555 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Add debugging info to assertion 



The WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp()) in
rcu_gp_cleanup() triggers (inexplicably, of course) every so often.
This commit therefore extracts more information.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent ce397d21

kernel/rcu/tree.c

+4 −1
Original line number Diff line number Diff line
@@ -2084,7 +2084,8 @@ static void rcu_gp_cleanup(struct rcu_state *rsp) 
	 */

	rcu_for_each_node_breadth_first(rsp, rnp) {

		raw_spin_lock_irq_rcu_node(rnp);

		WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp));

		if (WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)))

			dump_blkd_tasks(rnp, 10);

		WARN_ON_ONCE(rnp->qsmask);

		WRITE_ONCE(rnp->completed, rsp->gpnum);

		rdp = this_cpu_ptr(rsp->rda);
@@ -2294,6 +2295,7 @@ rcu_report_qs_rnp(unsigned long mask, struct rcu_state *rsp, 
			raw_spin_unlock_irqrestore_rcu_node(rnp, flags);

			return;

		}

		rnp->completedqs = rnp->gpnum;

		mask = rnp->grpmask;

		if (rnp->parent == NULL) {
@@ -3930,6 +3932,7 @@ static void __init rcu_init_one(struct rcu_state *rsp) 
						   &rcu_fqs_class[i], fqs[i]);

			rnp->gpnum = rsp->gpnum;

			rnp->completed = rsp->completed;

			rnp->completedqs = rsp->completed;

			rnp->qsmask = 0;

			rnp->qsmaskinit = 0;

			rnp->grplo = j * cpustride;

kernel/rcu/tree.h

+2 −0
Original line number Diff line number Diff line
@@ -87,6 +87,7 @@ struct rcu_node { 
	unsigned long completed; /* Last GP completed for this node. */

				/*  This will either be equal to or one */

				/*  behind the root rcu_node's gpnum. */

	unsigned long completedqs; /* All QSes done for this node. */

	unsigned long qsmask;	/* CPUs or groups that need to switch in */

				/*  order for current grace period to proceed.*/

				/*  In leaf rcu_node, each bit corresponds to */
@@ -453,6 +454,7 @@ static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp); 
static void rcu_preempt_check_callbacks(void);

void call_rcu(struct rcu_head *head, rcu_callback_t func);

static void __init __rcu_init_preempt(void);

static void dump_blkd_tasks(struct rcu_node *rnp, int ncheck);

static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags);

static void rcu_preempt_boost_start_gp(struct rcu_node *rnp);

static void invoke_rcu_callbacks_kthread(void);

kernel/rcu/tree_plugin.h

+36 −2
Original line number Diff line number Diff line
@@ -260,8 +260,10 @@ static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp) 
	 * ->exp_tasks pointers, respectively, to reference the newly

	 * blocked tasks.

	 */

	if (!rnp->gp_tasks && (blkd_state & RCU_GP_BLKD))

	if (!rnp->gp_tasks && (blkd_state & RCU_GP_BLKD)) {

		rnp->gp_tasks = &t->rcu_node_entry;

		WARN_ON_ONCE(rnp->completedqs == rnp->gpnum);

	}

	if (!rnp->exp_tasks && (blkd_state & RCU_EXP_BLKD))

		rnp->exp_tasks = &t->rcu_node_entry;

	WARN_ON_ONCE(!(blkd_state & RCU_GP_BLKD) !=
@@ -535,6 +537,8 @@ void rcu_read_unlock_special(struct task_struct *t) 
		WARN_ON_ONCE(rnp != t->rcu_blocked_node);

		WARN_ON_ONCE(!rcu_is_leaf_node(rnp));

		empty_norm = !rcu_preempt_blocked_readers_cgp(rnp);

		WARN_ON_ONCE(rnp->completedqs == rnp->gpnum &&

			     (!empty_norm || rnp->qsmask));

		empty_exp = sync_rcu_preempt_exp_done(rnp);

		smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */

		np = rcu_next_node_entry(t, rnp);
@@ -697,7 +701,8 @@ static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) 
	struct task_struct *t;



	RCU_LOCKDEP_WARN(preemptible(), "rcu_preempt_check_blocked_tasks() invoked with preemption enabled!!!\n");

	WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp));

	if (WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)))

		dump_blkd_tasks(rnp, 10);

	if (rcu_preempt_has_tasks(rnp)) {

		rnp->gp_tasks = rnp->blkd_tasks.next;

		t = container_of(rnp->gp_tasks, struct task_struct,
@@ -841,6 +846,27 @@ void exit_rcu(void) 
	__rcu_read_unlock();

}



/*

 * Dump the blocked-tasks state, but limit the list dump to the

 * specified number of elements.

 */

static void dump_blkd_tasks(struct rcu_node *rnp, int ncheck)

{

	int i;

	struct list_head *lhp;



	lockdep_assert_held(&rnp->lock);

	pr_info("%s: grp: %d-%d level: %d ->qamask %#lx ->gp_tasks %p ->boost_tasks %p ->exp_tasks %p &->blkd_tasks: %p offset: %u\n", __func__, rnp->grplo, rnp->grphi, rnp->level, rnp->qsmask, rnp->gp_tasks, rnp->boost_tasks, rnp->exp_tasks, &rnp->blkd_tasks, (unsigned int)offsetof(typeof(*rnp), blkd_tasks));

	pr_cont("\t->blkd_tasks");

	i = 0;

	list_for_each(lhp, &rnp->blkd_tasks) {

		pr_cont(" %p", lhp);

		if (++i >= 10)

			break;

	}

	pr_cont("\n");

}



#else /* #ifdef CONFIG_PREEMPT_RCU */



static struct rcu_state *const rcu_state_p = &rcu_sched_state;
@@ -949,6 +975,14 @@ void exit_rcu(void) 
{

}



/*

 * Dump the guaranteed-empty blocked-tasks state.  Trust but verify.

 */

static void dump_blkd_tasks(struct rcu_node *rnp, int ncheck)

{

	WARN_ON_ONCE(!list_empty(&rnp->blkd_tasks));

}



#endif /* #else #ifdef CONFIG_PREEMPT_RCU */



#ifdef CONFIG_RCU_BOOST