rcu: Add more diagnostics to expedited stall warning messages.

This commit adds print statements that check the rcu_node structure to
find which ->expmask bits and which ->exp_tasks structures are blocking
the current expedited grace period.

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

1 files changed, 21 insertions, 3 deletions

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index bc6b79716a86..6a652d1f3d7f 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3745,6 +3745,7 @@ static void synchronize_sched_expedited_wait(struct rcu_state *rsp)
         unsigned long jiffies_stall;
         unsigned long jiffies_start;
         unsigned long mask;
+        int ndetected;
         struct rcu_node *rnp;
         struct rcu_node *rnp_root = rcu_get_root(rsp);
         int ret;
@@ -3767,14 +3768,16 @@ static void synchronize_sched_expedited_wait(struct rcu_state *rsp)
                 }
                 pr_err("INFO: %s detected expedited stalls on CPUs/tasks: {",
                        rsp->name);
+                ndetected = 0;
                 rcu_for_each_leaf_node(rsp, rnp) {
-                        (void)rcu_print_task_exp_stall(rnp);
+                        ndetected = rcu_print_task_exp_stall(rnp);
                         mask = 1;
                         for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask <<= 1) {
                                 struct rcu_data *rdp;
 
                                 if (!(rnp->expmask & mask))
                                         continue;
+                                ndetected++;
                                 rdp = per_cpu_ptr(rsp->rda, cpu);
                                 pr_cont(" %d-%c%c%c", cpu,
                                         "O."[cpu_online(cpu)],
@@ -3783,8 +3786,23 @@ static void synchronize_sched_expedited_wait(struct rcu_state *rsp)
                         }
                         mask <<= 1;
                 }
-                pr_cont(" } %lu jiffies s: %lu\n",
-                        jiffies - jiffies_start, rsp->expedited_sequence);
+                pr_cont(" } %lu jiffies s: %lu root: %#lx/%c\n",
+                        jiffies - jiffies_start, rsp->expedited_sequence,
+                        rnp_root->expmask, ".T"[!!rnp_root->exp_tasks]);
+                if (!ndetected) {
+                        pr_err("blocking rcu_node structures:");
+                        rcu_for_each_node_breadth_first(rsp, rnp) {
+                                if (rnp == rnp_root)
+                                        continue; /* printed unconditionally */
+                                if (sync_rcu_preempt_exp_done(rnp))
+                                        continue;
+                                pr_cont(" l=%u:%d-%d:%#lx/%c",
+                                        rnp->level, rnp->grplo, rnp->grphi,
+                                        rnp->expmask,
+                                        ".T"[!!rnp->exp_tasks]);
+                        }
+                        pr_cont("\n");
+                }
                 rcu_for_each_leaf_node(rsp, rnp) {
                         mask = 1;
                         for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask <<= 1) {