rcutorture: Add ability to limit callback-flood intensity

The RCU tasks flavors of RCU now need concurrent callback flooding to
test their ability to switch between single-queue mode and per-CPU queue
mode, but their lack of heavy-duty forward-progress features rules out
the use of rcutorture's current callback-flooding code.  This commit
therefore provides the ability to limit the intensity of the callback
floods using a new ->cbflood_max field in the rcu_operations structure.
When this field is zero, there is no limit, otherwise, each callback-flood
kthread allocates at most ->cbflood_max callbacks.

Cc: Neeraj Upadhyay <neeraj.iitr10@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 9390f867ba6cc772189c53521e3469f6d85c69f2..1e8360d15920064cac8246b20300e2046a9b135f 100644 (file)
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -348,6 +348,7 @@ struct rcu_torture_ops {
        void (*gp_kthread_dbg)(void);
        bool (*check_boost_failed)(unsigned long gp_state, int *cpup);
        int (*stall_dur)(void);
+       long cbflood_max;
        int irq_capable;
        int can_boost;
        int extendables;
@@ -841,6 +842,7 @@ static struct rcu_torture_ops tasks_rude_ops = {
        .call           = call_rcu_tasks_rude,
        .cb_barrier     = rcu_barrier_tasks_rude,
        .gp_kthread_dbg = show_rcu_tasks_rude_gp_kthread,
+       .cbflood_max    = 50000,
        .fqs            = NULL,
        .stats          = NULL,
        .irq_capable    = 1,
@@ -881,6 +883,7 @@ static struct rcu_torture_ops tasks_tracing_ops = {
        .call           = call_rcu_tasks_trace,
        .cb_barrier     = rcu_barrier_tasks_trace,
        .gp_kthread_dbg = show_rcu_tasks_trace_gp_kthread,
+       .cbflood_max    = 50000,
        .fqs            = NULL,
        .stats          = NULL,
        .irq_capable    = 1,
@@ -2387,7 +2390,7 @@ static void rcu_torture_fwd_prog_cr(struct rcu_fwd *rfp)
                        rfp->rcu_fwd_cb_head = rfcpn;
                        n_launders++;
                        n_launders_sa++;
-               } else {
+               } else if (!cur_ops->cbflood_max || cur_ops->cbflood_max > n_max_cbs) {
                        rfcp = kmalloc(sizeof(*rfcp), GFP_KERNEL);
                        if (WARN_ON_ONCE(!rfcp)) {
                                schedule_timeout_interruptible(1);
@@ -2397,8 +2400,11 @@ static void rcu_torture_fwd_prog_cr(struct rcu_fwd *rfp)
                        n_launders_sa = 0;
                        rfcp->rfc_gps = 0;
                        rfcp->rfc_rfp = rfp;
+               } else {
+                       rfcp = NULL;
                }
-               cur_ops->call(&rfcp->rh, rcu_torture_fwd_cb_cr);
+               if (rfcp)
+                       cur_ops->call(&rfcp->rh, rcu_torture_fwd_cb_cr);
                rcu_torture_fwd_prog_cond_resched(n_launders + n_max_cbs);
                if (tick_nohz_full_enabled()) {
                        local_irq_save(flags);
@@ -2506,8 +2512,10 @@ static int rcu_torture_fwd_prog(void *args)
                pr_alert("%s: Starting forward-progress test %d\n", __func__, rfp->rcu_fwd_id);
                if (rcu_inkernel_boot_has_ended() && torture_num_online_cpus() > rfp->rcu_fwd_id)
                        rcu_torture_fwd_prog_cr(rfp);
-               if (!IS_ENABLED(CONFIG_TINY_RCU) ||
-                   (rcu_inkernel_boot_has_ended() && torture_num_online_cpus() > rfp->rcu_fwd_id))
+               if ((cur_ops->stall_dur && cur_ops->stall_dur() > 0) &&
+                   (!IS_ENABLED(CONFIG_TINY_RCU) ||
+                    (rcu_inkernel_boot_has_ended() &&
+                     torture_num_online_cpus() > rfp->rcu_fwd_id)))
                        rcu_torture_fwd_prog_nr(rfp, &tested, &tested_tries);
 
                /* Avoid slow periods, better to test when busy. */
@@ -2539,7 +2547,8 @@ static int __init rcu_torture_fwd_prog_init(void)
                fwd_progress = nr_cpu_ids;
        }
        if ((!cur_ops->sync && !cur_ops->call) ||
-           !cur_ops->stall_dur || cur_ops->stall_dur() <= 0 || cur_ops == &rcu_busted_ops) {
+           (!cur_ops->cbflood_max && (!cur_ops->stall_dur || cur_ops->stall_dur() <= 0)) ||
+           cur_ops == &rcu_busted_ops) {
                VERBOSE_TOROUT_STRING("rcu_torture_fwd_prog_init: Disabled, unsupported by RCU flavor under test");
                fwd_progress = 0;
                return 0;