3 files changed, 39 insertions, 10 deletions

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 5f1a11f1f7bc..a2503ef1bbe2 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1954,7 +1954,7 @@ static bool rcu_gp_init(struct rcu_state *rsp)
                 rcu_gp_slow(rsp, gp_init_delay);
                 raw_spin_lock_irqsave_rcu_node(rnp, flags);
                 rdp = this_cpu_ptr(rsp->rda);
-                rcu_preempt_check_blocked_tasks(rnp);
+                rcu_preempt_check_blocked_tasks(rsp, rnp);
                 rnp->qsmask = rnp->qsmaskinit;
                 WRITE_ONCE(rnp->gp_seq, rsp->gp_seq);
                 if (rnp == rdp->mynode)
@@ -2063,7 +2063,7 @@ static void rcu_gp_cleanup(struct rcu_state *rsp)
         rcu_for_each_node_breadth_first(rsp, rnp) {
                 raw_spin_lock_irq_rcu_node(rnp);
                 if (WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)))
-                        dump_blkd_tasks(rnp, 10);
+                        dump_blkd_tasks(rsp, rnp, 10);
                 WARN_ON_ONCE(rnp->qsmask);
                 WRITE_ONCE(rnp->gp_seq, new_gp_seq);
                 rdp = this_cpu_ptr(rsp->rda);
@@ -3516,6 +3516,10 @@ rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
         rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
         WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != 1);
         WARN_ON_ONCE(rcu_dynticks_in_eqs(rcu_dynticks_snap(rdp->dynticks)));
+        rdp->rcu_ofl_gp_seq = rsp->gp_seq;
+        rdp->rcu_ofl_gp_flags = RCU_GP_CLEANED;
+        rdp->rcu_onl_gp_seq = rsp->gp_seq;
+        rdp->rcu_onl_gp_flags = RCU_GP_CLEANED;
         rdp->cpu = cpu;
         rdp->rsp = rsp;
         rcu_boot_init_nocb_percpu_data(rdp);
@@ -3711,6 +3715,8 @@ void rcu_cpu_starting(unsigned int cpu)
                 /* Allow lockless access for expedited grace periods. */
                 smp_store_release(&rsp->ncpus, rsp->ncpus + nbits); /* ^^^ */
                 rcu_gpnum_ovf(rnp, rdp); /* Offline-induced counter wrap? */
+                rdp->rcu_onl_gp_seq = READ_ONCE(rsp->gp_seq);
+                rdp->rcu_onl_gp_flags = READ_ONCE(rsp->gp_flags);
                 if (rnp->qsmask & mask) { /* RCU waiting on incoming CPU? */
                         /* Report QS -after- changing ->qsmaskinitnext! */
                         rcu_report_qs_rnp(mask, rsp, rnp, rnp->gp_seq, flags);
@@ -3738,6 +3744,8 @@ static void rcu_cleanup_dying_idle_cpu(int cpu, struct rcu_state *rsp)
         mask = rdp->grpmask;
         spin_lock(&rsp->ofl_lock);
         raw_spin_lock_irqsave_rcu_node(rnp, flags); /* Enforce GP memory-order guarantee. */
+        rdp->rcu_ofl_gp_seq = READ_ONCE(rsp->gp_seq);
+        rdp->rcu_ofl_gp_flags = READ_ONCE(rsp->gp_flags);
         if (rnp->qsmask & mask) { /* RCU waiting on outgoing CPU? */
                 /* Report quiescent state -before- changing ->qsmaskinitnext! */
                 rcu_report_qs_rnp(mask, rsp, rnp, rnp->gp_seq, flags);
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 795d469c6f67..f52bc059bfec 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -255,12 +255,16 @@ struct rcu_data {
                                         /* Leader CPU takes GP-end wakeups. */
 #endif /* #ifdef CONFIG_RCU_NOCB_CPU */
 
-        /* 7) RCU CPU stall data. */
+        /* 7) Diagnostic data, including RCU CPU stall warnings. */
         unsigned int softirq_snap;      /* Snapshot of softirq activity. */
         /* ->rcu_iw* fields protected by leaf rcu_node ->lock. */
         struct irq_work rcu_iw;         /* Check for non-irq activity. */
         bool rcu_iw_pending;            /* Is ->rcu_iw pending? */
         unsigned long rcu_iw_gp_seq;    /* ->gp_seq associated with ->rcu_iw. */
+        unsigned long rcu_ofl_gp_seq;   /* ->gp_seq at last offline. */
+        short rcu_ofl_gp_flags;         /* ->gp_flags at last offline. */
+        unsigned long rcu_onl_gp_seq;   /* ->gp_seq at last online. */
+        short rcu_onl_gp_flags;         /* ->gp_flags at last online. */
 
         int cpu;
         struct rcu_state *rsp;
@@ -431,11 +435,13 @@ static bool rcu_preempt_has_tasks(struct rcu_node *rnp);
 static void rcu_print_detail_task_stall(struct rcu_state *rsp);
 static int rcu_print_task_stall(struct rcu_node *rnp);
 static int rcu_print_task_exp_stall(struct rcu_node *rnp);
-static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp);
+static void rcu_preempt_check_blocked_tasks(struct rcu_state *rsp,
+                                            struct rcu_node *rnp);
 static void rcu_preempt_check_callbacks(void);
 void call_rcu(struct rcu_head *head, rcu_callback_t func);
 static void __init __rcu_init_preempt(void);
-static void dump_blkd_tasks(struct rcu_node *rnp, int ncheck);
+static void dump_blkd_tasks(struct rcu_state *rsp, struct rcu_node *rnp,
+                            int ncheck);
 static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags);
 static void rcu_preempt_boost_start_gp(struct rcu_node *rnp);
 static void invoke_rcu_callbacks_kthread(void);
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index f45ff97b0d51..613372246a07 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -699,13 +699,14 @@ static int rcu_print_task_exp_stall(struct rcu_node *rnp)
  * Also, if there are blocked tasks on the list, they automatically
  * block the newly created grace period, so set up ->gp_tasks accordingly.
  */
-static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
+static void
+rcu_preempt_check_blocked_tasks(struct rcu_state *rsp, struct rcu_node *rnp)
 {
         struct task_struct *t;
 
         RCU_LOCKDEP_WARN(preemptible(), "rcu_preempt_check_blocked_tasks() invoked with preemption enabled!!!\n");
         if (WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)))
-                dump_blkd_tasks(rnp, 10);
+                dump_blkd_tasks(rsp, rnp, 10);
         if (rcu_preempt_has_tasks(rnp) &&
             (rnp->qsmaskinit || rnp->wait_blkd_tasks)) {
                 rnp->gp_tasks = rnp->blkd_tasks.next;
@@ -854,10 +855,14 @@ void exit_rcu(void)
  * Dump the blocked-tasks state, but limit the list dump to the
  * specified number of elements.
  */
-static void dump_blkd_tasks(struct rcu_node *rnp, int ncheck)
+static void
+dump_blkd_tasks(struct rcu_state *rsp, struct rcu_node *rnp, int ncheck)
 {
+        int cpu;
         int i;
         struct list_head *lhp;
+        bool onl;
+        struct rcu_data *rdp;
         struct rcu_node *rnp1;
 
         raw_lockdep_assert_held_rcu_node(rnp);
@@ -877,6 +882,14 @@ static void dump_blkd_tasks(struct rcu_node *rnp, int ncheck)
                         break;
         }
         pr_cont("\n");
+        for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++) {
+                rdp = per_cpu_ptr(rsp->rda, cpu);
+                onl = !!(rdp->grpmask & rcu_rnp_online_cpus(rnp));
+                pr_info("\t%d: %c online: %ld(%d) offline: %ld(%d)\n",
+                        cpu, ".o"[onl],
+                        (long)rdp->rcu_onl_gp_seq, rdp->rcu_onl_gp_flags,
+                        (long)rdp->rcu_ofl_gp_seq, rdp->rcu_ofl_gp_flags);
+        }
 }
 
 #else /* #ifdef CONFIG_PREEMPT_RCU */
@@ -949,7 +962,8 @@ static int rcu_print_task_exp_stall(struct rcu_node *rnp)
  * so there is no need to check for blocked tasks.  So check only for
  * bogus qsmask values.
  */
-static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
+static void
+rcu_preempt_check_blocked_tasks(struct rcu_state *rsp, struct rcu_node *rnp)
 {
         WARN_ON_ONCE(rnp->qsmask);
 }
@@ -990,7 +1004,8 @@ void exit_rcu(void)
 /*
  * Dump the guaranteed-empty blocked-tasks state.  Trust but verify.
  */
-static void dump_blkd_tasks(struct rcu_node *rnp, int ncheck)
+static void
+dump_blkd_tasks(struct rcu_state *rsp, struct rcu_node *rnp, int ncheck)
 {
         WARN_ON_ONCE(!list_empty(&rnp->blkd_tasks));
 }