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Commit f7a81b12 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu/nocb: Print no-CBs diagnostics when rcutorture writer unduly delayed 



This commit causes locking, sleeping, and callback state to be printed
for no-CBs CPUs when the rcutorture writer is delayed sufficiently for
rcutorture to complain.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.ibm.com>
parent 6aacd88d

kernel/rcu/rcutorture.c

+1 −0
Original line number Diff line number Diff line
@@ -2176,6 +2176,7 @@ rcu_torture_cleanup(void) 
		return;

	}



	show_rcu_gp_kthreads();

	rcu_torture_barrier_cleanup();

	torture_stop_kthread(rcu_torture_fwd_prog, fwd_prog_task);

	torture_stop_kthread(rcu_torture_stall, stall_task);

kernel/rcu/tree.h

+6 −1
Original line number Diff line number Diff line
@@ -212,7 +212,11 @@ struct rcu_data { 
	/* The following fields are used by GP kthread, hence own cacheline. */

	raw_spinlock_t nocb_gp_lock ____cacheline_internodealigned_in_smp;

	struct timer_list nocb_bypass_timer; /* Force nocb_bypass flush. */

	bool nocb_gp_sleep;		/* Is the nocb GP thread asleep? */

	u8 nocb_gp_sleep;		/* Is the nocb GP thread asleep? */

	u8 nocb_gp_bypass;		/* Found a bypass on last scan? */

	u8 nocb_gp_gp;			/* GP to wait for on last scan? */

	unsigned long nocb_gp_seq;	/*  If so, ->gp_seq to wait for. */

	unsigned long nocb_gp_loops;	/* # passes through wait code. */

	struct swait_queue_head nocb_gp_wq; /* For nocb kthreads to sleep on. */

	bool nocb_cb_sleep;		/* Is the nocb CB thread asleep? */

	struct task_struct *nocb_cb_kthread;
@@ -438,6 +442,7 @@ static void do_nocb_deferred_wakeup(struct rcu_data *rdp); 
static void rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp);

static void rcu_spawn_cpu_nocb_kthread(int cpu);

static void __init rcu_spawn_nocb_kthreads(void);

static void show_rcu_nocb_state(struct rcu_data *rdp);

static void rcu_nocb_lock(struct rcu_data *rdp);

static void rcu_nocb_unlock(struct rcu_data *rdp);

static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp,

kernel/rcu/tree_plugin.h

+82 −0
Original line number Diff line number Diff line
@@ -2021,6 +2021,9 @@ static void nocb_gp_wait(struct rcu_data *my_rdp) 
			rcu_gp_kthread_wake();

	}



	my_rdp->nocb_gp_bypass = bypass;

	my_rdp->nocb_gp_gp = needwait_gp;

	my_rdp->nocb_gp_seq = needwait_gp ? wait_gp_seq : 0;

	if (bypass && !rcu_nocb_poll) {

		// At least one child with non-empty ->nocb_bypass, so set

		// timer in order to avoid stranding its callbacks.
@@ -2055,6 +2058,7 @@ static void nocb_gp_wait(struct rcu_data *my_rdp) 
		WRITE_ONCE(my_rdp->nocb_gp_sleep, true);

		raw_spin_unlock_irqrestore(&my_rdp->nocb_gp_lock, flags);

	}

	my_rdp->nocb_gp_seq = -1;

	WARN_ON(signal_pending(current));

}
@@ -2071,6 +2075,7 @@ static int rcu_nocb_gp_kthread(void *arg) 
	struct rcu_data *rdp = arg;



	for (;;) {

		WRITE_ONCE(rdp->nocb_gp_loops, rdp->nocb_gp_loops + 1);

		nocb_gp_wait(rdp);

		cond_resched_tasks_rcu_qs();

	}
@@ -2362,6 +2367,79 @@ void rcu_bind_current_to_nocb(void) 
}

EXPORT_SYMBOL_GPL(rcu_bind_current_to_nocb);



/*

 * Dump out nocb grace-period kthread state for the specified rcu_data

 * structure.

 */

static void show_rcu_nocb_gp_state(struct rcu_data *rdp)

{

	struct rcu_node *rnp = rdp->mynode;



	pr_info("nocb GP %d %c%c%c%c%c%c %c[%c%c] %c%c:%ld rnp %d:%d %lu\n",

		rdp->cpu,

		"kK"[!!rdp->nocb_gp_kthread],

		"lL"[raw_spin_is_locked(&rdp->nocb_gp_lock)],

		"dD"[!!rdp->nocb_defer_wakeup],

		"tT"[timer_pending(&rdp->nocb_timer)],

		"bB"[timer_pending(&rdp->nocb_bypass_timer)],

		"sS"[!!rdp->nocb_gp_sleep],

		".W"[swait_active(&rdp->nocb_gp_wq)],

		".W"[swait_active(&rnp->nocb_gp_wq[0])],

		".W"[swait_active(&rnp->nocb_gp_wq[1])],

		".B"[!!rdp->nocb_gp_bypass],

		".G"[!!rdp->nocb_gp_gp],

		(long)rdp->nocb_gp_seq,

		rnp->grplo, rnp->grphi, READ_ONCE(rdp->nocb_gp_loops));

}



/* Dump out nocb kthread state for the specified rcu_data structure. */

static void show_rcu_nocb_state(struct rcu_data *rdp)

{

	struct rcu_segcblist *rsclp = &rdp->cblist;

	bool waslocked;

	bool wastimer;

	bool wassleep;



	if (rdp->nocb_gp_rdp == rdp)

		show_rcu_nocb_gp_state(rdp);



	pr_info("   CB %d->%d %c%c%c%c%c%c F%ld L%ld C%d %c%c%c%c%c q%ld\n",

		rdp->cpu, rdp->nocb_gp_rdp->cpu,

		"kK"[!!rdp->nocb_cb_kthread],

		"bB"[raw_spin_is_locked(&rdp->nocb_bypass_lock)],

		"cC"[!!atomic_read(&rdp->nocb_lock_contended)],

		"lL"[raw_spin_is_locked(&rdp->nocb_lock)],

		"sS"[!!rdp->nocb_cb_sleep],

		".W"[swait_active(&rdp->nocb_cb_wq)],

		jiffies - rdp->nocb_bypass_first,

		jiffies - rdp->nocb_nobypass_last,

		rdp->nocb_nobypass_count,

		".D"[rcu_segcblist_ready_cbs(rsclp)],

		".W"[!rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL)],

		".R"[!rcu_segcblist_restempty(rsclp, RCU_WAIT_TAIL)],

		".N"[!rcu_segcblist_restempty(rsclp, RCU_NEXT_READY_TAIL)],

		".B"[!!rcu_cblist_n_cbs(&rdp->nocb_bypass)],

		rcu_segcblist_n_cbs(&rdp->cblist));



	/* It is OK for GP kthreads to have GP state. */

	if (rdp->nocb_gp_rdp == rdp)

		return;



	waslocked = raw_spin_is_locked(&rdp->nocb_gp_lock);

	wastimer = timer_pending(&rdp->nocb_timer);

	wassleep = swait_active(&rdp->nocb_gp_wq);

	if (!rdp->nocb_defer_wakeup && !rdp->nocb_gp_sleep &&

	    !waslocked && !wastimer && !wassleep)

		return;  /* Nothing untowards. */



	pr_info("   !!! %c%c%c%c %c\n",

		"lL"[waslocked],

		"dD"[!!rdp->nocb_defer_wakeup],

		"tT"[wastimer],

		"sS"[!!rdp->nocb_gp_sleep],

		".W"[wassleep]);

}



#else /* #ifdef CONFIG_RCU_NOCB_CPU */



/* No ->nocb_lock to acquire.  */
@@ -2439,6 +2517,10 @@ static void __init rcu_spawn_nocb_kthreads(void) 
{

}



static void show_rcu_nocb_state(struct rcu_data *rdp)

{

}



#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */



/*

kernel/rcu/tree_stall.h

+5 −0
Original line number Diff line number Diff line
@@ -589,6 +589,11 @@ void show_rcu_gp_kthreads(void) 
				cpu, (long)rdp->gp_seq_needed);

		}

	}

	for_each_possible_cpu(cpu) {

		rdp = per_cpu_ptr(&rcu_data, cpu);

		if (rcu_segcblist_is_offloaded(&rdp->cblist))

			show_rcu_nocb_state(rdp);

	}

	/* sched_show_task(rcu_state.gp_kthread); */

}

EXPORT_SYMBOL_GPL(show_rcu_gp_kthreads);