From: "Paul E. McKenney" <paul...@linux.vnet.ibm.com>
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: Paul E. McKenney <paul...@linux.vnet.ibm.com>
---
kernel/rcu/rcutorture.c | 129 +++++++++++++++++++++++++++++++++++++++-
1 file changed, 127 insertions(+), 2 deletions(-)
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 210c77460365..8cf700ca7845 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -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());
--
2.17.1
