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>

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index bc6b797..6a652d1 100644 (file)
--- 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) {