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>

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>
Paul E. McKenney · Ingo Molnar
1 parent 6155fec92e
Showing 4 changed files with 69 additions and 0 deletions Side-by-side Diff
kernel/rcutree.c
kernel/rcutree.h
kernel/rcutree_plugin.h
lib/Kconfig.debug
@@ -489,6 +489,10 @@
 	       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. */
 }
  
@@ -352,6 +352,7 @@
 				      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);
@@ -312,7 +312,51 @@
  
 #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.
  */
@@ -759,6 +803,14 @@
 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
  
 #ifdef CONFIG_RCU_CPU_STALL_DETECTOR
+
+/*
+ * 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
@@ -781,6 +781,18 @@
  
 	  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
...	...	@@ -489,6 +489,10 @@
489	489	smp_processor_id(), (long)(jiffies - rsp->gp_start));
490	490	trigger_all_cpu_backtrace();
491	491
	492	+ /* If so configured, complain about tasks blocking the grace period. */
	493	+
	494	+ rcu_print_detail_task_stall(rsp);
	495	+
492	496	force_quiescent_state(rsp, 0); /* Kick them all. */
493	497	}
494	498
...	...	@@ -352,6 +352,7 @@
352	352	unsigned long flags);
353	353	#endif /* #ifdef CONFIG_HOTPLUG_CPU */
354	354	#ifdef CONFIG_RCU_CPU_STALL_DETECTOR
	355	+static void rcu_print_detail_task_stall(struct rcu_state *rsp);
355	356	static void rcu_print_task_stall(struct rcu_node *rnp);
356	357	#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
357	358	static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp);
...	...	@@ -312,7 +312,51 @@
312	312
313	313	#ifdef CONFIG_RCU_CPU_STALL_DETECTOR
314	314
	315	+#ifdef CONFIG_RCU_CPU_STALL_VERBOSE
	316	+
315	317	/*
	318	+ * Dump detailed information for all tasks blocking the current RCU
	319	+ * grace period on the specified rcu_node structure.
	320	+ */
	321	+static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
	322	+{
	323	+ unsigned long flags;
	324	+ struct list_head *lp;
	325	+ int phase;
	326	+ struct task_struct *t;
	327	+
	328	+ if (rcu_preempted_readers(rnp)) {
	329	+ raw_spin_lock_irqsave(&rnp->lock, flags);
	330	+ phase = rnp->gpnum & 0x1;
	331	+ lp = &rnp->blocked_tasks[phase];
	332	+ list_for_each_entry(t, lp, rcu_node_entry)
	333	+ sched_show_task(t);
	334	+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
	335	+ }
	336	+}
	337	+
	338	+/*
	339	+ * Dump detailed information for all tasks blocking the current RCU
	340	+ * grace period.
	341	+ */
	342	+static void rcu_print_detail_task_stall(struct rcu_state *rsp)
	343	+{
	344	+ struct rcu_node *rnp = rcu_get_root(rsp);
	345	+
	346	+ rcu_print_detail_task_stall_rnp(rnp);
	347	+ rcu_for_each_leaf_node(rsp, rnp)
	348	+ rcu_print_detail_task_stall_rnp(rnp);
	349	+}
	350	+
	351	+#else /* #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
	352	+
	353	+static void rcu_print_detail_task_stall(struct rcu_state *rsp)
	354	+{
	355	+}
	356	+
	357	+#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
	358	+
	359	+/*
316	360	* Scan the current list of tasks blocked within RCU read-side critical
317	361	* sections, printing out the tid of each.
318	362	*/
...	...	@@ -759,6 +803,14 @@
759	803	#endif /* #ifdef CONFIG_HOTPLUG_CPU */
760	804
761	805	#ifdef CONFIG_RCU_CPU_STALL_DETECTOR
	806	+
	807	+/*
	808	+ * Because preemptable RCU does not exist, we never have to check for
	809	+ * tasks blocked within RCU read-side critical sections.
	810	+ */
	811	+static void rcu_print_detail_task_stall(struct rcu_state *rsp)
	812	+{
	813	+}
762	814
763	815	/*
764	816	* Because preemptable RCU does not exist, we never have to check for
...	...	@@ -781,6 +781,18 @@
781	781
782	782	Say Y if you are unsure.
783	783
	784	+config RCU_CPU_STALL_VERBOSE
	785	+ bool "Print additional per-task information for RCU_CPU_STALL_DETECTOR"
	786	+ depends on RCU_CPU_STALL_DETECTOR && TREE_PREEMPT_RCU
	787	+ default n
	788	+ help
	789	+ This option causes RCU to printk detailed per-task information
	790	+ for any tasks that are stalling the current RCU grace period.
	791	+
	792	+ Say N if you are unsure.
	793	+
	794	+ Say Y if you want to enable such checks.
	795	+
784	796	config KPROBES_SANITY_TEST
785	797	bool "Kprobes sanity tests"
786	798	depends on DEBUG_KERNEL