rcu: Add RCU_CPU_STALL_VERBOSE to dump detailed per-task information

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>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference: <1266887105-1528-21-git-send-email-paulmck@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index b07be37..525d398 100644 (file)
--- 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 (file)
--- 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 (file)
--- 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 (file)
--- 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