rcu: Add CPU online/offline state to dump_blkd_tasks()

Interactions between CPU-hotplug operations and grace-period
initialization can result in dump_blkd_tasks().  One of the first
debugging actions in this case is to search back in dmesg to work
out which of the affected rcu_node structure's CPUs are online and to
determine the last CPU-hotplug operation affecting any of those CPUs.
This can be laborious and error-prone, especially when console output
is lost.

This commit therefore causes dump_blkd_tasks() to dump the state of
the affected rcu_node structure's CPUs and the last grace period during
which the last offline and online operation affected each of these CPUs.

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

1 files changed, 10 insertions, 2 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);