rcutorture: Print histogram of CB invocation at OOM time

One reason why a forward-progress test might fail would be if something
prevented or delayed callback invocation.  This commit therefore adds a
callback-invocation histogram printout when OOM is reported to rcutorture.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>

1 files changed, 16 insertions, 8 deletions

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index f28b88ecb47a..329f4fb13125 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -1631,6 +1631,20 @@ static bool rcu_fwd_emergency_stop;
 #define MIN_FWD_CBS_LAUNDERED   100     /* Number of counted CBs. */
 static long n_launders_hist[2 * MAX_FWD_CB_JIFFIES / HZ];
 
+static void rcu_torture_fwd_cb_hist(void)
+{
+        int i;
+        int j;
+
+        for (i = ARRAY_SIZE(n_launders_hist) - 1; i > 0; i--)
+                if (n_launders_hist[i] > 0)
+                        break;
+        pr_alert("%s: Callback-invocation histogram:", __func__);
+        for (j = 0; j <= i; j++)
+                pr_cont(" %ds: %ld", j + 1, n_launders_hist[j]);
+        pr_cont("\n");
+}
+
 /* Callback function for continuous-flood RCU callbacks. */
 static void rcu_torture_fwd_cb_cr(struct rcu_head *rhp)
 {
@@ -1718,7 +1732,6 @@ static void rcu_torture_fwd_prog_cr(void)
         unsigned long cver;
         unsigned long gps;
         int i;
-        int j;
         long n_launders;
         long n_launders_cb_snap;
         long n_launders_sa;
@@ -1791,13 +1804,7 @@ static void rcu_torture_fwd_prog_cr(void)
                          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");
+                rcu_torture_fwd_cb_hist();
         }
 }
 
@@ -1809,6 +1816,7 @@ static void rcu_torture_fwd_prog_cr(void)
 static int rcutorture_oom_notify(struct notifier_block *self,
                                  unsigned long notused, void *nfreed)
 {
+        rcu_torture_fwd_cb_hist();
         rcu_fwd_progress_check(1 + (jiffies - READ_ONCE(rcu_fwd_startat) / 2));
         WRITE_ONCE(rcu_fwd_emergency_stop, true);
         return NOTIFY_OK;