rcutorture: Export RCU grace-period kthread wait state to rcutorture

This commit allows rcutorture to print additional state for the
RCU grace-period kthreads in cases where RCU seems reluctant to
start a new grace period.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

3 files changed, 25 insertions, 1 deletions

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 9decce0f110c..37ae5e1d4a1d 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -1034,6 +1034,7 @@ rcu_torture_printk(char *page)
                                 "??? Writer stall state %d g%lu c%lu f%#x\n",
                                 rcu_torture_writer_state,
                                 gpnum, completed, flags);
+                show_rcu_gp_kthreads();
                 rcutorture_trace_dump();
         }
         rtcv_snap = rcu_torture_current_version;
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 3d15b5a82ae8..93e64381aa2a 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -280,6 +280,21 @@ void rcu_bh_force_quiescent_state(void)
 EXPORT_SYMBOL_GPL(rcu_bh_force_quiescent_state);
 
 /*
+ * Show the state of the grace-period kthreads.
+ */
+void show_rcu_gp_kthreads(void)
+{
+        struct rcu_state *rsp;
+
+        for_each_rcu_flavor(rsp) {
+                pr_info("%s: wait state: %d ->state: %#lx\n",
+                        rsp->name, rsp->gp_state, rsp->gp_kthread->state);
+                /* sched_show_task(rsp->gp_kthread); */
+        }
+}
+EXPORT_SYMBOL_GPL(show_rcu_gp_kthreads);
+
+/*
  * Record the number of times rcutorture tests have been initiated and
  * terminated.  This information allows the debugfs tracing stats to be
  * correlated to the rcutorture messages, even when the rcutorture module
@@ -1626,6 +1641,7 @@ static int __noreturn rcu_gp_kthread(void *arg)
                         trace_rcu_grace_period(rsp->name,
                                                ACCESS_ONCE(rsp->gpnum),
                                                TPS("reqwait"));
+                        rsp->gp_state = RCU_GP_WAIT_GPS;
                         wait_event_interruptible(rsp->gp_wq,
                                                  ACCESS_ONCE(rsp->gp_flags) &
                                                  RCU_GP_FLAG_INIT);
@@ -1653,6 +1669,7 @@ static int __noreturn rcu_gp_kthread(void *arg)
                         trace_rcu_grace_period(rsp->name,
                                                ACCESS_ONCE(rsp->gpnum),
                                                TPS("fqswait"));
+                        rsp->gp_state = RCU_GP_WAIT_FQS;
                         ret = wait_event_interruptible_timeout(rsp->gp_wq,
                                         ((gf = ACCESS_ONCE(rsp->gp_flags)) &
                                          RCU_GP_FLAG_FQS) ||
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 75dc3c39a02a..c2fd1e722879 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -406,7 +406,8 @@ struct rcu_state {
         unsigned long completed;                /* # of last completed gp. */
         struct task_struct *gp_kthread;         /* Task for grace periods. */
         wait_queue_head_t gp_wq;                /* Where GP task waits. */
-        int gp_flags;                           /* Commands for GP task. */
+        short gp_flags;                         /* Commands for GP task. */
+        short gp_state;                         /* GP kthread sleep state. */
 
         /* End of fields guarded by root rcu_node's lock. */
 
@@ -469,6 +470,11 @@ struct rcu_state {
 #define RCU_GP_FLAG_INIT 0x1    /* Need grace-period initialization. */
 #define RCU_GP_FLAG_FQS  0x2    /* Need grace-period quiescent-state forcing. */
 
+/* Values for rcu_state structure's gp_flags field. */
+#define RCU_GP_WAIT_INIT 0      /* Initial state. */
+#define RCU_GP_WAIT_GPS  1      /* Wait for grace-period start. */
+#define RCU_GP_WAIT_FQS  2      /* Wait for force-quiescent-state time. */
+
 extern struct list_head rcu_struct_flavors;
 
 /* Sequence through rcu_state structures for each RCU flavor. */