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Commit 57738942 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Add CPU online/offline state to dump_blkd_tasks() 



Interactions between CPU-hotplug operations and grace-period
initialization can result in dump_blkd_tasks().  One of the first
debugging actions in this case is to search back in dmesg to work
out which of the affected rcu_node structure's CPUs are online and to
determine the last CPU-hotplug operation affecting any of those CPUs.
This can be laborious and error-prone, especially when console output
is lost.

This commit therefore causes dump_blkd_tasks() to dump the state of
the affected rcu_node structure's CPUs and the last grace period during
which the last offline and online operation affected each of these CPUs.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent ff3cee39

kernel/rcu/tree.c

+10 −2
Original line number Diff line number Diff line
@@ -1954,7 +1954,7 @@ static bool rcu_gp_init(struct rcu_state *rsp) 
		rcu_gp_slow(rsp, gp_init_delay);

		raw_spin_lock_irqsave_rcu_node(rnp, flags);

		rdp = this_cpu_ptr(rsp->rda);

		rcu_preempt_check_blocked_tasks(rnp);

		rcu_preempt_check_blocked_tasks(rsp, rnp);

		rnp->qsmask = rnp->qsmaskinit;

		WRITE_ONCE(rnp->gp_seq, rsp->gp_seq);

		if (rnp == rdp->mynode)
@@ -2063,7 +2063,7 @@ static void rcu_gp_cleanup(struct rcu_state *rsp) 
	rcu_for_each_node_breadth_first(rsp, rnp) {

		raw_spin_lock_irq_rcu_node(rnp);

		if (WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)))

			dump_blkd_tasks(rnp, 10);

			dump_blkd_tasks(rsp, rnp, 10);

		WARN_ON_ONCE(rnp->qsmask);

		WRITE_ONCE(rnp->gp_seq, new_gp_seq);

		rdp = this_cpu_ptr(rsp->rda);
@@ -3516,6 +3516,10 @@ rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp) 
	rdp->dynticks = &per_cpu(rcu_dynticks, cpu);

	WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != 1);

	WARN_ON_ONCE(rcu_dynticks_in_eqs(rcu_dynticks_snap(rdp->dynticks)));

	rdp->rcu_ofl_gp_seq = rsp->gp_seq;

	rdp->rcu_ofl_gp_flags = RCU_GP_CLEANED;

	rdp->rcu_onl_gp_seq = rsp->gp_seq;

	rdp->rcu_onl_gp_flags = RCU_GP_CLEANED;

	rdp->cpu = cpu;

	rdp->rsp = rsp;

	rcu_boot_init_nocb_percpu_data(rdp);
@@ -3711,6 +3715,8 @@ void rcu_cpu_starting(unsigned int cpu) 
		/* Allow lockless access for expedited grace periods. */

		smp_store_release(&rsp->ncpus, rsp->ncpus + nbits); /* ^^^ */

		rcu_gpnum_ovf(rnp, rdp); /* Offline-induced counter wrap? */

		rdp->rcu_onl_gp_seq = READ_ONCE(rsp->gp_seq);

		rdp->rcu_onl_gp_flags = READ_ONCE(rsp->gp_flags);

		if (rnp->qsmask & mask) { /* RCU waiting on incoming CPU? */

			/* Report QS -after- changing ->qsmaskinitnext! */

			rcu_report_qs_rnp(mask, rsp, rnp, rnp->gp_seq, flags);
@@ -3738,6 +3744,8 @@ static void rcu_cleanup_dying_idle_cpu(int cpu, struct rcu_state *rsp) 
	mask = rdp->grpmask;

	spin_lock(&rsp->ofl_lock);

	raw_spin_lock_irqsave_rcu_node(rnp, flags); /* Enforce GP memory-order guarantee. */

	rdp->rcu_ofl_gp_seq = READ_ONCE(rsp->gp_seq);

	rdp->rcu_ofl_gp_flags = READ_ONCE(rsp->gp_flags);

	if (rnp->qsmask & mask) { /* RCU waiting on outgoing CPU? */

		/* Report quiescent state -before- changing ->qsmaskinitnext! */

		rcu_report_qs_rnp(mask, rsp, rnp, rnp->gp_seq, flags);

kernel/rcu/tree.h

+9 −3
Original line number Diff line number Diff line
@@ -255,12 +255,16 @@ struct rcu_data { 
					/* Leader CPU takes GP-end wakeups. */

#endif /* #ifdef CONFIG_RCU_NOCB_CPU */



	/* 7) RCU CPU stall data. */

	/* 7) Diagnostic data, including RCU CPU stall warnings. */

	unsigned int softirq_snap;	/* Snapshot of softirq activity. */

	/* ->rcu_iw* fields protected by leaf rcu_node ->lock. */

	struct irq_work rcu_iw;		/* Check for non-irq activity. */

	bool rcu_iw_pending;		/* Is ->rcu_iw pending? */

	unsigned long rcu_iw_gp_seq;	/* ->gp_seq associated with ->rcu_iw. */

	unsigned long rcu_ofl_gp_seq;	/* ->gp_seq at last offline. */

	short rcu_ofl_gp_flags;		/* ->gp_flags at last offline. */

	unsigned long rcu_onl_gp_seq;	/* ->gp_seq at last online. */

	short rcu_onl_gp_flags;		/* ->gp_flags at last online. */



	int cpu;

	struct rcu_state *rsp;
@@ -431,11 +435,13 @@ static bool rcu_preempt_has_tasks(struct rcu_node *rnp); 
static void rcu_print_detail_task_stall(struct rcu_state *rsp);

static int rcu_print_task_stall(struct rcu_node *rnp);

static int rcu_print_task_exp_stall(struct rcu_node *rnp);

static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp);

static void rcu_preempt_check_blocked_tasks(struct rcu_state *rsp,

					    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 dump_blkd_tasks(struct rcu_state *rsp, 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

+20 −5
Original line number Diff line number Diff line
@@ -699,13 +699,14 @@ static int rcu_print_task_exp_stall(struct rcu_node *rnp) 
 * Also, if there are blocked tasks on the list, they automatically

 * block the newly created grace period, so set up ->gp_tasks accordingly.

 */

static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)

static void

rcu_preempt_check_blocked_tasks(struct rcu_state *rsp, struct rcu_node *rnp)

{

	struct task_struct *t;



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

	if (WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)))

		dump_blkd_tasks(rnp, 10);

		dump_blkd_tasks(rsp, rnp, 10);

	if (rcu_preempt_has_tasks(rnp) &&

	    (rnp->qsmaskinit || rnp->wait_blkd_tasks)) {

		rnp->gp_tasks = rnp->blkd_tasks.next;
@@ -854,10 +855,14 @@ void exit_rcu(void) 
 * 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)

static void

dump_blkd_tasks(struct rcu_state *rsp, struct rcu_node *rnp, int ncheck)

{

	int cpu;

	int i;

	struct list_head *lhp;

	bool onl;

	struct rcu_data *rdp;

	struct rcu_node *rnp1;



	raw_lockdep_assert_held_rcu_node(rnp);
@@ -877,6 +882,14 @@ static void dump_blkd_tasks(struct rcu_node *rnp, int ncheck) 
			break;

	}

	pr_cont("\n");

	for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++) {

		rdp = per_cpu_ptr(rsp->rda, cpu);

		onl = !!(rdp->grpmask & rcu_rnp_online_cpus(rnp));

		pr_info("\t%d: %c online: %ld(%d) offline: %ld(%d)\n",

			cpu, ".o"[onl],

			(long)rdp->rcu_onl_gp_seq, rdp->rcu_onl_gp_flags,

			(long)rdp->rcu_ofl_gp_seq, rdp->rcu_ofl_gp_flags);

	}

}



#else /* #ifdef CONFIG_PREEMPT_RCU */
@@ -949,7 +962,8 @@ static int rcu_print_task_exp_stall(struct rcu_node *rnp) 
 * so there is no need to check for blocked tasks.  So check only for

 * bogus qsmask values.

 */

static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)

static void

rcu_preempt_check_blocked_tasks(struct rcu_state *rsp, struct rcu_node *rnp)

{

	WARN_ON_ONCE(rnp->qsmask);

}
@@ -990,7 +1004,8 @@ 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)

static void

dump_blkd_tasks(struct rcu_state *rsp, struct rcu_node *rnp, int ncheck)

{

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

}