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Subject[PATCH tip/core/rcu 21/21] rcu: add RCU_CPU_STALL_VERBOSE to dump detailed per-task information
Date
When RCU detects a grace-period stall, it currently just prints out the
PID of any tasks doing the stalling. This patch adds RCU_CPU_STALL_VERBOSE,
which enables the more-verbose reporting from sched_show_task().

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
kernel/rcutree.c | 4 +++
kernel/rcutree.h | 1 +
kernel/rcutree_plugin.h | 52 +++++++++++++++++++++++++++++++++++++++++++++++
lib/Kconfig.debug | 12 ++++++++++
4 files changed, 69 insertions(+), 0 deletions(-)

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index b07be37..525d398 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -489,6 +489,10 @@ static void print_other_cpu_stall(struct rcu_state *rsp)
smp_processor_id(), (long)(jiffies - rsp->gp_start));
trigger_all_cpu_backtrace();

+ /* If so configured, complain about tasks blocking the grace period. */
+
+ rcu_print_detail_task_stall(rsp);
+
force_quiescent_state(rsp, 0); /* Kick them all. */
}

diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index 6a82c34..2ceb083 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -352,6 +352,7 @@ static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp,
unsigned long flags);
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
#ifdef CONFIG_RCU_CPU_STALL_DETECTOR
+static void rcu_print_detail_task_stall(struct rcu_state *rsp);
static void rcu_print_task_stall(struct rcu_node *rnp);
#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp);
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index aecfe37..3516de7 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -312,6 +312,50 @@ EXPORT_SYMBOL_GPL(__rcu_read_unlock);

#ifdef CONFIG_RCU_CPU_STALL_DETECTOR

+#ifdef CONFIG_RCU_CPU_STALL_VERBOSE
+
+/*
+ * Dump detailed information for all tasks blocking the current RCU
+ * grace period on the specified rcu_node structure.
+ */
+static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
+{
+ unsigned long flags;
+ struct list_head *lp;
+ int phase;
+ struct task_struct *t;
+
+ if (rcu_preempted_readers(rnp)) {
+ raw_spin_lock_irqsave(&rnp->lock, flags);
+ phase = rnp->gpnum & 0x1;
+ lp = &rnp->blocked_tasks[phase];
+ list_for_each_entry(t, lp, rcu_node_entry)
+ sched_show_task(t);
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
+ }
+}
+
+/*
+ * Dump detailed information for all tasks blocking the current RCU
+ * grace period.
+ */
+static void rcu_print_detail_task_stall(struct rcu_state *rsp)
+{
+ struct rcu_node *rnp = rcu_get_root(rsp);
+
+ rcu_print_detail_task_stall_rnp(rnp);
+ rcu_for_each_leaf_node(rsp, rnp)
+ rcu_print_detail_task_stall_rnp(rnp);
+}
+
+#else /* #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
+
+static void rcu_print_detail_task_stall(struct rcu_state *rsp)
+{
+}
+
+#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
+
/*
* Scan the current list of tasks blocked within RCU read-side critical
* sections, printing out the tid of each.
@@ -764,6 +808,14 @@ static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
* Because preemptable RCU does not exist, we never have to check for
* tasks blocked within RCU read-side critical sections.
*/
+static void rcu_print_detail_task_stall(struct rcu_state *rsp)
+{
+}
+
+/*
+ * Because preemptable RCU does not exist, we never have to check for
+ * tasks blocked within RCU read-side critical sections.
+ */
static void rcu_print_task_stall(struct rcu_node *rnp)
{
}
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 6af20a8..4cdab45 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -781,6 +781,18 @@ config RCU_CPU_STALL_DETECTOR

Say Y if you are unsure.

+config RCU_CPU_STALL_VERBOSE
+ bool "Print additional per-task information for RCU_CPU_STALL_DETECTOR"
+ depends on RCU_CPU_STALL_DETECTOR && TREE_PREEMPT_RCU
+ default n
+ help
+ This option causes RCU to printk detailed per-task information
+ for any tasks that are stalling the current RCU grace period.
+
+ Say N if you are unsure.
+
+ Say Y if you want to enable such checks.
+
config KPROBES_SANITY_TEST
bool "Kprobes sanity tests"
depends on DEBUG_KERNEL
--
1.6.6


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