rcu: Provide more diagnostics for stalled GP kthread

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

2 files changed, 13 insertions, 3 deletions

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 65137bc28b2b..1c58cbd03922 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1178,9 +1178,11 @@ static void rcu_check_gp_kthread_starvation(struct rcu_state *rsp)
         j = jiffies;
         gpa = READ_ONCE(rsp->gp_activity);
         if (j - gpa > 2 * HZ)
-                pr_err("%s kthread starved for %ld jiffies! g%lu c%lu f%#x\n",
+                pr_err("%s kthread starved for %ld jiffies! g%lu c%lu f%#x s%d ->state=%#lx\n",
                        rsp->name, j - gpa,
-                       rsp->gpnum, rsp->completed, rsp->gp_flags);
+                       rsp->gpnum, rsp->completed,
+                       rsp->gp_flags, rsp->gp_state,
+                       rsp->gp_kthread ? rsp->gp_kthread->state : 0);
 }
 
 /*
@@ -2041,6 +2043,7 @@ static int __noreturn rcu_gp_kthread(void *arg)
                         wait_event_interruptible(rsp->gp_wq,
                                                  READ_ONCE(rsp->gp_flags) &
                                                  RCU_GP_FLAG_INIT);
+                        rsp->gp_state = RCU_GP_DONE_GPS;
                         /* Locking provides needed memory barrier. */
                         if (rcu_gp_init(rsp))
                                 break;
@@ -2073,6 +2076,7 @@ static int __noreturn rcu_gp_kthread(void *arg)
                                         (!READ_ONCE(rnp->qsmask) &&
                                          !rcu_preempt_blocked_readers_cgp(rnp)),
                                         j);
+                        rsp->gp_state = RCU_GP_DONE_FQS;
                         /* Locking provides needed memory barriers. */
                         /* If grace period done, leave loop. */
                         if (!READ_ONCE(rnp->qsmask) &&
@@ -2110,7 +2114,9 @@ static int __noreturn rcu_gp_kthread(void *arg)
                 }
 
                 /* Handle grace-period end. */
+                rsp->gp_state = RCU_GP_CLEANUP;
                 rcu_gp_cleanup(rsp);
+                rsp->gp_state = RCU_GP_CLEANED;
         }
 }
 
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 4adb7ca0bf47..f1f4784f9107 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -527,7 +527,11 @@ struct rcu_state {
 /* 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. */
+#define RCU_GP_DONE_GPS  2      /* Wait done for grace-period start. */
+#define RCU_GP_WAIT_FQS  3      /* Wait for force-quiescent-state time. */
+#define RCU_GP_DONE_FQS  4      /* Wait done for force-quiescent-state time. */
+#define RCU_GP_CLEANUP   5      /* Grace-period cleanup started. */
+#define RCU_GP_CLEANED   6      /* Grace-period cleanup complete. */
 
 extern struct list_head rcu_struct_flavors;