[PATCH 4/9] rcu: Add running and boosted indications to RCU task stall dump

["Paul E. McKenney" <paulmck@kernel.org>]

Currently, rcu_print_task_stall() will dump out the PID, RCU reader
nesting level, the rcu_special structure's flags, and whether or not
that reader is on the ->blkd_tasks list.  When debugging RCU priority
boosting, it is also good to know whether the stalled RCU reader is
currently running and whether it is currently being RCU priority boosted.
This commit therefore adds this information to the output.

[ paulmck: Apply kernel test robot feedback. ]

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/tree_stall.h | 23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index 93ba31a619b6..5dded1e89197 100644
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -11,6 +11,7 @@
 #include <linux/kvm_para.h>
 #include <linux/rcu_notifier.h>
 #include <linux/smp.h>
+#include <linux/rtmutex.h>
 
 //////////////////////////////////////////////////////////////////////////////
 //
@@ -305,6 +306,8 @@ struct rcu_stall_chk_rdr {
 	int nesting;
 	union rcu_special rs;
 	bool on_blkd_list;
+	bool rcu_rdr_running;
+	int rcu_rdr_boosted;
 };
 
 /*
@@ -313,6 +316,7 @@ struct rcu_stall_chk_rdr {
  */
 static int check_slow_task(struct task_struct *t, void *arg)
 {
+	struct rcu_node *rnp;
 	struct rcu_stall_chk_rdr *rscrp = arg;
 
 	if (task_curr(t))
@@ -320,6 +324,19 @@ static int check_slow_task(struct task_struct *t, void *arg)
 	rscrp->nesting = t->rcu_read_lock_nesting;
 	rscrp->rs = t->rcu_read_unlock_special;
 	rscrp->on_blkd_list = !list_empty(&t->rcu_node_entry);
+	rscrp->rcu_rdr_running = task_curr(t);
+	rscrp->rcu_rdr_boosted = 0;
+	if (rscrp->on_blkd_list) {
+		rnp = READ_ONCE(t->rcu_blocked_node);
+		raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
+		if (rnp == READ_ONCE(t->rcu_blocked_node)) {
+			if (rt_mutex_owner(&rnp->boost_mtx.rtmutex) == t)
+				rscrp->rcu_rdr_boosted = 1;
+		} else {
+			rscrp->rcu_rdr_boosted = 2;
+		}
+		raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
+	}
 	return 0;
 }
 
@@ -357,12 +374,14 @@ static int rcu_print_task_stall(struct rcu_node *rnp, unsigned long flags)
 		if (task_call_func(t, check_slow_task, &rscr))
 			pr_cont(" P%d", t->pid);
 		else
-			pr_cont(" P%d/%d:%c%c%c%c",
+			pr_cont(" P%d/%d:%c%c%c%c%c%c",
 				t->pid, rscr.nesting,
 				".b"[rscr.rs.b.blocked],
 				".q"[rscr.rs.b.need_qs],
 				".e"[rscr.rs.b.exp_hint],
-				".l"[rscr.on_blkd_list]);
+				".l"[rscr.on_blkd_list],
+				".R"[rscr.rcu_rdr_running],
+				".B?"[rscr.rcu_rdr_boosted]);
 		lockdep_assert_irqs_disabled();
 		put_task_struct(t);
 		ndetected++;
-- 
2.40.1