From fb81a44b88e6173ed0f6e9d6a1afa5305fb63f6e Mon Sep 17 00:00:00 2001
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Date: Wed, 17 Dec 2014 08:35:02 -0800
Subject: [PATCH] rcu: Add GP-kthread-starvation checks to CPU stall warnings
This commit adds a message that is printed if the relevant grace-period
kthread has not been able to run for the two seconds preceding the
stall warning. (The two seconds is double the maximum interval between
successive bouts of quiescent-state forcing.)
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
Documentation/RCU/stallwarn.txt | 9 +++++++++
kernel/rcu/tree.c | 21 ++++++++++++++++++++-
2 files changed, 29 insertions(+), 1 deletion(-)
diff --git a/Documentation/RCU/stallwarn.txt b/Documentation/RCU/stallwarn.txt
index 55f9707fe60a..53e7d2856db6 100644
--- a/Documentation/RCU/stallwarn.txt
+++ b/Documentation/RCU/stallwarn.txt
@@ -152,6 +152,15 @@ no non-lazy callbacks ("." is printed otherwise, as shown above) and
"D" indicates that dyntick-idle processing is enabled ("." is printed
otherwise, for example, if disabled via the "nohz=" kernel boot parameter).
+If the relevant grace-period kthread has been unable to run prior to
+the stall warning, the following additional line is printed:
+
+ rcu_preempt kthread starved for 2023 jiffies!
+
+Starving the grace-period kthreads of CPU time can of course result in
+RCU CPU stall warnings even when all CPUs and tasks have passed through
+the required quiescent states.
+
Multiple Warnings From One Stall
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index cb00e038c2f2..e335f33d0b9f 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1072,6 +1072,21 @@ static void record_gp_stall_check_time(struct rcu_state *rsp)
rsp->n_force_qs_gpstart = ACCESS_ONCE(rsp->n_force_qs);
}
+/*
+ * Complain about starvation of grace-period kthread.
+ */
+static void rcu_check_gp_kthread_starvation(struct rcu_state *rsp)
+{
+ unsigned long gpa;
+ unsigned long j;
+
+ j = jiffies;
+ gpa = ACCESS_ONCE(rsp->gp_activity);
+ if (j - gpa > 2 * HZ)
+ pr_err("%s kthread starved for %ld jiffies!\n",
+ rsp->name, j - gpa);
+}
+
/*
* Dump stacks of all tasks running on stalled CPUs.
*/
@@ -1169,9 +1184,10 @@ static void print_other_cpu_stall(struct rcu_state *rsp, unsigned long gpnum)
}
/* Complain about tasks blocking the grace period. */
-
rcu_print_detail_task_stall(rsp);
+ rcu_check_gp_kthread_starvation(rsp);
+
force_quiescent_state(rsp); /* Kick them all. */
}
@@ -1196,6 +1212,9 @@ static void print_cpu_stall(struct rcu_state *rsp)
pr_cont(" (t=%lu jiffies g=%ld c=%ld q=%lu)\n",
jiffies - rsp->gp_start,
(long)rsp->gpnum, (long)rsp->completed, totqlen);
+
+ rcu_check_gp_kthread_starvation(rsp);
+
rcu_dump_cpu_stacks(rsp);
raw_spin_lock_irqsave(&rnp->lock, flags);
--
2.34.1