rcutorture: Add forward-progress checking for writer

The rcutorture output currently does not distinguish between stalls in
the RCU implementation and stalls in the rcu_torture_writer() kthreads.
This commit therefore adds some diagnostics to help distinguish between
these two conditions, at least for the non-SRCU implementations.  (SRCU
does not provide evidence of update-side forward progress by design.)

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

1 files changed, 33 insertions, 0 deletions

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 0c47e300210a..3d15b5a82ae8 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -294,6 +294,39 @@ void rcutorture_record_test_transition(void)
 EXPORT_SYMBOL_GPL(rcutorture_record_test_transition);
 
 /*
+ * Send along grace-period-related data for rcutorture diagnostics.
+ */
+void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
+                            unsigned long *gpnum, unsigned long *completed)
+{
+        struct rcu_state *rsp = NULL;
+
+        switch (test_type) {
+        case RCU_FLAVOR:
+                rsp = rcu_state;
+                break;
+        case RCU_BH_FLAVOR:
+                rsp = &rcu_bh_state;
+                break;
+        case RCU_SCHED_FLAVOR:
+                rsp = &rcu_sched_state;
+                break;
+        default:
+                break;
+        }
+        if (rsp != NULL) {
+                *flags = ACCESS_ONCE(rsp->gp_flags);
+                *gpnum = ACCESS_ONCE(rsp->gpnum);
+                *completed = ACCESS_ONCE(rsp->completed);
+                return;
+        }
+        *flags = 0;
+        *gpnum = 0;
+        *completed = 0;
+}
+EXPORT_SYMBOL_GPL(rcutorture_get_gp_data);
+
+/*
  * Record the number of writer passes through the current rcutorture test.
  * This is also used to correlate debugfs tracing stats with the rcutorture
  * messages.