[PATCH 2/5] rcutorture: Print number of RCU up/down readers and migrations

[Paul E. McKenney]

This commit prints the number of RCU up/down readers and the number
of such readers that migrated from one CPU to another, along
with the rest of the periodic rcu_torture_stats_print() output.
These statistics are currently used only by srcu_down_read{,_fast}()
and srcu_up_read(,_fast)().

Signed-off-by: Paul E. McKenney <paul...@kernel.org>
---
 kernel/rcu/rcutorture.c | 30 +++++++++++++++++++++++++-----
 1 file changed, 25 insertions(+), 5 deletions(-)

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 0e044afa98d32..21ff365fca5d9 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -2447,9 +2447,11 @@ struct rcu_torture_one_read_state_updown {
        struct hrtimer rtorsu_hrt;
        bool rtorsu_inuse;
        ktime_t rtorsu_kt;
+       int rtorsu_cpu;
        unsigned long rtorsu_j;
        unsigned long rtorsu_ndowns;
        unsigned long rtorsu_nups;
+       unsigned long rtorsu_nmigrates;
        struct torture_random_state rtorsu_trs;
        struct rcu_torture_one_read_state rtorsu_rtors;
 };
@@ -2460,12 +2462,15 @@ static int rcu_torture_updown(void *arg);
 
 static enum hrtimer_restart rcu_torture_updown_hrt(struct hrtimer *hrtp)
 {
+       int cpu = raw_smp_processor_id();
        struct rcu_torture_one_read_state_updown *rtorsup;
 
        rtorsup = container_of(hrtp, struct rcu_torture_one_read_state_updown, 
rtorsu_hrt);
        rcu_torture_one_read_end(&rtorsup->rtorsu_rtors, &rtorsup->rtorsu_trs, 
-1);
        WARN_ONCE(rtorsup->rtorsu_nups >= rtorsup->rtorsu_ndowns, "%s: Up 
without matching down #%zu.\n", __func__, rtorsup - updownreaders);
-       rtorsup->rtorsu_nups++;
+       WRITE_ONCE(rtorsup->rtorsu_nups, rtorsup->rtorsu_nups + 1);
+       WRITE_ONCE(rtorsup->rtorsu_nmigrates,
+                  rtorsup->rtorsu_nmigrates + (cpu != rtorsup->rtorsu_cpu));
        smp_store_release(&rtorsup->rtorsu_inuse, false);
        return HRTIMER_NORESTART;
 }
@@ -2513,7 +2518,7 @@ static void rcu_torture_updown_cleanup(void)
                if (hrtimer_cancel(&rtorsup->rtorsu_hrt) || 
WARN_ON_ONCE(rtorsup->rtorsu_inuse)) {
                        rcu_torture_one_read_end(&rtorsup->rtorsu_rtors, 
&rtorsup->rtorsu_trs, -1);
                        WARN_ONCE(rtorsup->rtorsu_nups >= 
rtorsup->rtorsu_ndowns, "%s: Up without matching down #%zu.\n", __func__, 
rtorsup - updownreaders);
-                       rtorsup->rtorsu_nups++;
+                       WRITE_ONCE(rtorsup->rtorsu_nups, rtorsup->rtorsu_nups + 
1);
                        smp_store_release(&rtorsup->rtorsu_inuse, false);
                }
 
@@ -2531,13 +2536,14 @@ static void rcu_torture_updown_one(struct 
rcu_torture_one_read_state_updown *rto
 
        init_rcu_torture_one_read_state(&rtorsup->rtorsu_rtors, 
&rtorsup->rtorsu_trs);
        rawidx = cur_ops->down_read();
-       rtorsup->rtorsu_ndowns++;
+       WRITE_ONCE(rtorsup->rtorsu_ndowns, rtorsup->rtorsu_ndowns + 1);
        idx = (rawidx << RCUTORTURE_RDR_SHIFT_1) & RCUTORTURE_RDR_MASK_1;
        rtorsup->rtorsu_rtors.readstate = idx | RCUTORTURE_RDR_UPDOWN;
        rtorsup->rtorsu_rtors.rtrsp++;
+       rtorsup->rtorsu_cpu = raw_smp_processor_id();
        if (!rcu_torture_one_read_start(&rtorsup->rtorsu_rtors, 
&rtorsup->rtorsu_trs, -1)) {
                WARN_ONCE(rtorsup->rtorsu_nups >= rtorsup->rtorsu_ndowns, "%s: 
Up without matching down #%zu.\n", __func__, rtorsup - updownreaders);
-               rtorsup->rtorsu_nups++;
+               WRITE_ONCE(rtorsup->rtorsu_nups, rtorsup->rtorsu_nups + 1);
                schedule_timeout_idle(HZ);
                return;
        }
@@ -2646,6 +2652,10 @@ rcu_torture_stats_print(void)
        long pipesummary[RCU_TORTURE_PIPE_LEN + 1] = { 0 };
        long batchsummary[RCU_TORTURE_PIPE_LEN + 1] = { 0 };
        long n_gpwraps = 0;
+       unsigned long ndowns = 0;
+       unsigned long nunexpired = 0;
+       unsigned long nmigrates = 0;
+       unsigned long nups = 0;
        struct rcu_torture *rtcp;
        static unsigned long rtcv_snap = ULONG_MAX;
        static bool splatted;
@@ -2659,10 +2669,18 @@ rcu_torture_stats_print(void)
                if (cur_ops->get_gpwrap_count)
                        n_gpwraps += cur_ops->get_gpwrap_count(cpu);
        }
+       if (updownreaders) {
+               for (i = 0; i < n_up_down; i++) {
+                       ndowns += READ_ONCE(updownreaders[i].rtorsu_ndowns);
+                       nups += READ_ONCE(updownreaders[i].rtorsu_nups);
+                       nunexpired += READ_ONCE(updownreaders[i].rtorsu_inuse);
+                       nmigrates += 
READ_ONCE(updownreaders[i].rtorsu_nmigrates);
+               }
+       }
        for (i = RCU_TORTURE_PIPE_LEN; i >= 0; i--) {
                if (pipesummary[i] != 0)
                        break;
-       }
+       } // The value of variable "i" is used later, so don't clobber it!
 
        pr_alert("%s%s ", torture_type, TORTURE_FLAG);
        rtcp = rcu_access_pointer(rcu_torture_current);
@@ -2683,6 +2701,8 @@ rcu_torture_stats_print(void)
                n_rcu_torture_boost_failure,
                n_rcu_torture_boosts,
                atomic_long_read(&n_rcu_torture_timers));
+       if (updownreaders)
+               pr_cont("ndowns: %lu nups: %lu nhrt: %lu nmigrates: %lu ", 
ndowns, nups, nunexpired,  nmigrates);
        torture_onoff_stats();
        pr_cont("barrier: %ld/%ld:%ld ",
                data_race(n_barrier_successes),
-- 
2.40.1