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Commit 48718485 authored by Paul E. McKenney's avatar Paul E. McKenney Committed by Paul E. McKenney
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rcutorture: Add call_rcu() flooding forward-progress tests 



This commit adds a call_rcu() flooding loop to the forward-progress test.
This emulates tight userspace loops that force call_rcu() invocations,
for example, the infamous loop containing close(open()) that instigated
the addition of blimit.  If RCU does not make sufficient forward progress
in invoking the resulting flood of callbacks, rcutorture emits a warning.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent eaaf055f

kernel/rcu/rcutorture.c

+127 −2
Original line number Diff line number Diff line
@@ -259,6 +259,8 @@ static atomic_t barrier_cbs_invoked; /* Barrier callbacks invoked. */ 
static wait_queue_head_t *barrier_cbs_wq; /* Coordinate barrier testing. */

static DECLARE_WAIT_QUEUE_HEAD(barrier_wq);



static bool rcu_fwd_cb_nodelay;		/* Short rcu_torture_delay() delays. */



/*

 * Allocate an element from the rcu_tortures pool.

 */
@@ -348,7 +350,8 @@ rcu_read_delay(struct torture_random_state *rrsp, struct rt_read_seg *rtrsp) 
	 * period, and we want a long delay occasionally to trigger

	 * force_quiescent_state. */



	if (!(torture_random(rrsp) % (nrealreaders * 2000 * longdelay_ms))) {

	if (!rcu_fwd_cb_nodelay &&

	    !(torture_random(rrsp) % (nrealreaders * 2000 * longdelay_ms))) {

		started = cur_ops->get_gp_seq();

		ts = rcu_trace_clock_local();

		if (preempt_count() & (SOFTIRQ_MASK | HARDIRQ_MASK))
@@ -1674,6 +1677,43 @@ static void rcu_torture_fwd_prog_cb(struct rcu_head *rhp) 
	cur_ops->call(&fcsp->rh, rcu_torture_fwd_prog_cb);

}



/* State for continuous-flood RCU callbacks. */

struct rcu_fwd_cb {

	struct rcu_head rh;

	struct rcu_fwd_cb *rfc_next;

	int rfc_gps;

};

static DEFINE_SPINLOCK(rcu_fwd_lock);

static struct rcu_fwd_cb *rcu_fwd_cb_head;

static struct rcu_fwd_cb **rcu_fwd_cb_tail = &rcu_fwd_cb_head;

static long n_launders_cb;

static unsigned long rcu_fwd_startat;

#define MAX_FWD_CB_JIFFIES	(8 * HZ) /* Maximum CB test duration. */

#define MIN_FWD_CB_LAUNDERS	3	/* This many CB invocations to count. */

#define MIN_FWD_CBS_LAUNDERED	100	/* Number of counted CBs. */

static long n_launders_hist[2 * MAX_FWD_CB_JIFFIES / HZ];



/* Callback function for continuous-flood RCU callbacks. */

static void rcu_torture_fwd_cb_cr(struct rcu_head *rhp)

{

	int i;

	struct rcu_fwd_cb *rfcp = container_of(rhp, struct rcu_fwd_cb, rh);

	struct rcu_fwd_cb **rfcpp;



	rfcp->rfc_next = NULL;

	rfcp->rfc_gps++;

	spin_lock(&rcu_fwd_lock);

	rfcpp = rcu_fwd_cb_tail;

	rcu_fwd_cb_tail = &rfcp->rfc_next;

	WRITE_ONCE(*rfcpp, rfcp);

	WRITE_ONCE(n_launders_cb, n_launders_cb + 1);

	i = ((jiffies - rcu_fwd_startat) / HZ);

	if (i >= ARRAY_SIZE(n_launders_hist))

		i = ARRAY_SIZE(n_launders_hist) - 1;

	n_launders_hist[i]++;

	spin_unlock(&rcu_fwd_lock);

}



/* Carry out grace-period forward-progress testing. */

static int rcu_torture_fwd_prog(void *args)

{
@@ -1681,11 +1721,21 @@ static int rcu_torture_fwd_prog(void *args) 
	unsigned long dur;

	struct fwd_cb_state fcs;

	unsigned long gps;

	int i;

	int idx;

	int j;

	long n_launders;

	long n_launders_cb_snap;

	long n_launders_sa;

	long n_max_cbs;

	long n_max_gps;

	struct rcu_fwd_cb *rfcp;

	struct rcu_fwd_cb *rfcpn;

	int sd;

	int sd4;

	bool selfpropcb = false;

	unsigned long stopat;

	unsigned long stoppedat;

	int tested = 0;

	int tested_tries = 0;

	static DEFINE_TORTURE_RANDOM(trs);
@@ -1699,6 +1749,8 @@ static int rcu_torture_fwd_prog(void *args) 
	}

	do {

		schedule_timeout_interruptible(fwd_progress_holdoff * HZ);



		/* Tight loop containing cond_resched(). */

		if  (selfpropcb) {

			WRITE_ONCE(fcs.stop, 0);

			cur_ops->call(&fcs.rh, rcu_torture_fwd_prog_cb);
@@ -1708,7 +1760,8 @@ static int rcu_torture_fwd_prog(void *args) 
		sd = cur_ops->stall_dur() + 1;

		sd4 = (sd + fwd_progress_div - 1) / fwd_progress_div;

		dur = sd4 + torture_random(&trs) % (sd - sd4);

		stopat = jiffies + dur;

		rcu_fwd_startat = jiffies;

		stopat = rcu_fwd_startat + dur;

		while (time_before(jiffies, stopat) && !torture_must_stop()) {

			idx = cur_ops->readlock();

			udelay(10);
@@ -1729,6 +1782,78 @@ static int rcu_torture_fwd_prog(void *args) 
			cur_ops->sync(); /* Wait for running CB to complete. */

			cur_ops->cb_barrier(); /* Wait for queued callbacks. */

		}



		/* Loop continuously posting RCU callbacks. */

		WRITE_ONCE(rcu_fwd_cb_nodelay, true);

		cur_ops->sync(); /* Later readers see above write. */

		rcu_fwd_startat = jiffies;

		stopat = rcu_fwd_startat + MAX_FWD_CB_JIFFIES;

		n_launders = 0;

		n_launders_cb = 0;

		n_launders_sa = 0;

		n_max_cbs = 0;

		n_max_gps = 0;

		for (i = 0; i < ARRAY_SIZE(n_launders_hist); i++)

			n_launders_hist[i] = 0;

		cver = READ_ONCE(rcu_torture_current_version);

		gps = cur_ops->get_gp_seq();

		while (time_before(jiffies, stopat) && !torture_must_stop()) {

			rfcp = READ_ONCE(rcu_fwd_cb_head);

			rfcpn = NULL;

			if (rfcp)

				rfcpn = READ_ONCE(rfcp->rfc_next);

			if (rfcpn) {

				if (rfcp->rfc_gps >= MIN_FWD_CB_LAUNDERS &&

				    ++n_max_gps >= MIN_FWD_CBS_LAUNDERED)

					break;

				rcu_fwd_cb_head = rfcpn;

				n_launders++;

				n_launders_sa++;

			} else {

				rfcp = kmalloc(sizeof(*rfcp), GFP_KERNEL);

				if (WARN_ON_ONCE(!rfcp)) {

					schedule_timeout_interruptible(1);

					continue;

				}

				n_max_cbs++;

				n_launders_sa = 0;

				rfcp->rfc_gps = 0;

			}

			cur_ops->call(&rfcp->rh, rcu_torture_fwd_cb_cr);

			cond_resched();

		}

		stoppedat = jiffies;

		n_launders_cb_snap = READ_ONCE(n_launders_cb);

		cver = READ_ONCE(rcu_torture_current_version) - cver;

		gps = rcutorture_seq_diff(cur_ops->get_gp_seq(), gps);

		cur_ops->cb_barrier(); /* Wait for callbacks to be invoked. */

		for (;;) {

			rfcp = rcu_fwd_cb_head;

			if (!rfcp)

				break;

			rcu_fwd_cb_head = rfcp->rfc_next;

			kfree(rfcp);

		}

		rcu_fwd_cb_tail = &rcu_fwd_cb_head;

		WRITE_ONCE(rcu_fwd_cb_nodelay, false);

		if (!torture_must_stop()) {

			WARN_ON(n_max_gps < MIN_FWD_CBS_LAUNDERED);

			pr_alert("%s Duration %lu barrier: %lu pending %ld n_launders: %ld n_launders_sa: %ld n_max_gps: %ld n_max_cbs: %ld cver %ld gps %ld\n",

				 __func__,

				 stoppedat - rcu_fwd_startat,

				 jiffies - stoppedat,

				 n_launders + n_max_cbs - n_launders_cb_snap,

				 n_launders, n_launders_sa,

				 n_max_gps, n_max_cbs, cver, gps);

			for (i = ARRAY_SIZE(n_launders_hist) - 1; i > 0; i--)

				if (n_launders_hist[i] > 0)

					break;

			pr_alert("Callback-invocation histogram:");

			for (j = 0; j <= i; j++)

				pr_cont(" %ds: %ld", j + 1, n_launders_hist[j]);

			pr_cont("\n");

		}



		/* Avoid slow periods, better to test when busy. */

		stutter_wait("rcu_torture_fwd_prog");

	} while (!torture_must_stop());