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From:   "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To:     linux-kernel@vger.kernel.org
Cc:     mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com,
        akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
        josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
        rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
        fweisbec@gmail.com, oleg@redhat.com, joel.opensrc@gmail.com,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 17/22] EXP: rcu: Abstract addition of debugging information to assertion
Date:   Sun, 22 Apr 2018 19:32:22 -0700
In-Reply-To: <20180423023150.GA21533@linux.vnet.ibm.com>
References: <20180423023150.GA21533@linux.vnet.ibm.com>
Message-Id: <1524450747-22778-17-git-send-email-paulmck@linux.vnet.ibm.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Signed-off-by: Paul E. McKenney <paulmck@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