[PATCH tip/core/rcu 17/22] EXP: rcu: Abstract addition of debugging information to assertion

[Paul E. McKenney]

Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
---
 kernel/rcu/tree.c        | 18 ++----------------
 kernel/rcu/tree.h        |  1 +
 kernel/rcu/tree_plugin.h | 29 +++++++++++++++++++++++++++++
 3 files changed, 32 insertions(+), 16 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 6ad2ac34558f..3bfd1519d378 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2147,22 +2147,8 @@ static void rcu_gp_cleanup(struct rcu_state *rsp)
         */
        rcu_for_each_node_breadth_first(rsp, rnp) {
                raw_spin_lock_irq_rcu_node(rnp);
-#ifdef CONFIG_PREEMPT_RCU
-               if (WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp))) {
-                       int i;
-                       struct task_struct *t;
-
-                       pr_info("%s: grp: %d-%d level: %d ->gp_tasks %p 
->exp_tasks %p &->blkd_tasks: %p offset: %u\n", __func__, rnp->grplo, 
rnp->grphi, rnp->level, rnp->gp_tasks, rnp->exp_tasks, &rnp->blkd_tasks, 
(unsigned int)offsetof(typeof(*rnp), blkd_tasks));
-                       pr_cont("\t->blkd_tasks");
-                       i = 0;
-                       list_for_each_entry(t, &rnp->blkd_tasks, 
rcu_node_entry) {
-                               pr_cont(" %p", t);
-                               if (++i >= 10)
-                                       break;
-                       }
-                       pr_cont("\n");
-               }
-#endif /* #ifdef CONFIG_PREEMPT_RCU */
+               if (WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)))
+                       dump_blkd_tasks(rnp, 10);
                WARN_ON_ONCE(rnp->qsmask);
                WRITE_ONCE(rnp->completed, rsp->gpnum);
                rdp = this_cpu_ptr(rsp->rda);
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 0b3a90ebe225..23ae7c00d3c5 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -428,6 +428,7 @@ static void rcu_preempt_check_blocked_tasks(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 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 b999032e9466..a2ae6b49f900 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -841,6 +841,27 @@ void exit_rcu(void)
        __rcu_read_unlock();
 }
 
+/*
+ * 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)
+{
+       int i;
+       struct list_head *lhp;
+
+       lockdep_assert_held(&rnp->lock);
+       pr_info("%s: grp: %d-%d level: %d ->gp_tasks %p ->exp_tasks %p 
&->blkd_tasks: %p offset: %u\n", __func__, rnp->grplo, rnp->grphi, rnp->level, 
rnp->gp_tasks, rnp->exp_tasks, &rnp->blkd_tasks, (unsigned 
int)offsetof(typeof(*rnp), blkd_tasks));
+       pr_cont("\t->blkd_tasks");
+       i = 0;
+       list_for_each(lhp, &rnp->blkd_tasks) {
+               pr_cont(" %p", lhp);
+               if (++i >= 10)
+                       break;
+       }
+       pr_cont("\n");
+}
+
 #else /* #ifdef CONFIG_PREEMPT_RCU */
 
 static struct rcu_state *const rcu_state_p = &rcu_sched_state;
@@ -949,6 +970,14 @@ 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)
+{
+       WARN_ON_ONCE(!list_empty(&rnp->blkd_tasks));
+}
+
 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
 
 #ifdef CONFIG_RCU_BOOST
-- 
2.5.2