rcutorture: Combine n_max_cbs from all kthreads in a callback flood

With the addition of multiple callback-flood kthreads, the maximum number
of callbacks from any one of those kthreads is reported in the rcutorture
run summary. This commit changes this to report the sum of each kthread's
maximum number of callbacks in a given callback-flooding episode.

Cc: Neeraj Upadhyay <[e-mail]>
Signed-off-by: Paul E. McKenney <[e-mail]>

kernel/rcu/rcutorture.c

···
 static DEFINE_MUTEX(rcu_fwd_mutex);
 static struct rcu_fwd *rcu_fwds;
 static unsigned long rcu_fwd_seq;
+static atomic_long_t rcu_fwd_max_cbs;
 static bool rcu_fwd_emergency_stop;
 
 static void rcu_torture_fwd_cb_hist(struct rcu_fwd *rfp)
···
 			 n_launders + n_max_cbs - n_launders_cb_snap,
 			 n_launders, n_launders_sa,
 			 n_max_gps, n_max_cbs, cver, gps);
+		atomic_long_add(n_max_cbs, &rcu_fwd_max_cbs);
 		rcu_torture_fwd_cb_hist(rfp);
 	}
 	schedule_timeout_uninterruptible(HZ); /* Let CBs drain. */
···
 /* Carry out grace-period forward-progress testing. */
 static int rcu_torture_fwd_prog(void *args)
 {
+	bool firsttime = true;
+	long max_cbs;
 	int oldnice = task_nice(current);
 	unsigned long oldseq = READ_ONCE(rcu_fwd_seq);
 	struct rcu_fwd *rfp = args;
···
 		if (!rfp->rcu_fwd_id) {
 			schedule_timeout_interruptible(fwd_progress_holdoff * HZ);
 			WRITE_ONCE(rcu_fwd_emergency_stop, false);
+			if (!firsttime) {
+				max_cbs = atomic_long_xchg(&rcu_fwd_max_cbs, 0);
+				pr_alert("%s n_max_cbs: %ld\n", __func__, max_cbs);
+			}
+			firsttime = false;
 			WRITE_ONCE(rcu_fwd_seq, rcu_fwd_seq + 1);
 		} else {
 			while (READ_ONCE(rcu_fwd_seq) == oldseq)

tools/testing/selftests/rcutorture/bin/kvm-recheck-rcu.sh

···
 	    tail -1 | sed -e 's/^\[[ 0-9.]*] //' |
 	    awk '{ print \"[\" $1 \" \" $5 \" \" $6 \" \" $7 \"]\"; }' |
 	    tr -d '\012\015'`"
-fwdprog="`grep 'rcu_torture_fwd_prog_cr Duration' $i/console.log 2> /dev/null | sed -e 's/^\[[^]]*] //' | sort -k15nr | head -1 | awk '{ print $14 " " $15 }'`"
+fwdprog="`grep 'rcu_torture_fwd_prog n_max_cbs: ' $i/console.log 2> /dev/null | sed -e 's/^\[[^]]*] //' | sort -k3nr | head -1 | awk '{ print $2 " " $3 }'`"
 if test -z "$ngps"
 then
 	echo "$configfile ------- " $stopstate