rcu: permit suppressing current grace period's CPU stall warnings

When using a kernel debugger, a long sojourn in the debugger can get
you lots of RCU CPU stall warnings once you resume.  This might not be
helpful, especially if you are using the system console.  This patch
therefore allows RCU CPU stall warnings to be suppressed, but only for
the duration of the current set of grace periods.

This differs from Jason's original patch in that it adds support for
tiny RCU and preemptible RCU, and uses a slightly different method for
suppressing the RCU CPU stall warning messages.

Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: Jason Wessel <jason.wessel@windriver.com>

diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index 4cc5eba41616c25283e4e168ca01cec38b9bb9e2..3fa179784e18b24bcce5258e718d7e34a4bb21bc 100644 (file)
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -178,6 +178,10 @@ static inline void rcu_sched_force_quiescent_state(void)
 {
 }
 
+static inline void rcu_cpu_stall_reset(void)
+{
+}
+
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 
 extern int rcu_scheduler_active __read_mostly;

diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index c13b85dd22bc2f4503eaec6b4747d8db003c46b6..0726809497ba8d006cd144508bbc6908e9d8ca52 100644 (file)
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -36,6 +36,7 @@ extern void rcu_sched_qs(int cpu);
 extern void rcu_bh_qs(int cpu);
 extern void rcu_note_context_switch(int cpu);
 extern int rcu_needs_cpu(int cpu);
+extern void rcu_cpu_stall_reset(void);
 
 #ifdef CONFIG_TREE_PREEMPT_RCU
 

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index ff214118e4b8d683da53b035f466b664e9172938..42140a860bb997614af85de2f8515e2cb330b8f1 100644 (file)
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -565,6 +565,22 @@ static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr)
        return NOTIFY_DONE;
 }
 
+/**
+ * rcu_cpu_stall_reset - prevent further stall warnings in current grace period
+ *
+ * Set the stall-warning timeout way off into the future, thus preventing
+ * any RCU CPU stall-warning messages from appearing in the current set of
+ * RCU grace periods.
+ *
+ * The caller must disable hard irqs.
+ */
+void rcu_cpu_stall_reset(void)
+{
+       rcu_sched_state.jiffies_stall = jiffies + ULONG_MAX / 2;
+       rcu_bh_state.jiffies_stall = jiffies + ULONG_MAX / 2;
+       rcu_preempt_stall_reset();
+}
+
 static struct notifier_block rcu_panic_block = {
        .notifier_call = rcu_panic,
 };
@@ -584,6 +600,10 @@ static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
 {
 }
 
+void rcu_cpu_stall_reset(void)
+{
+}
+
 static void __init check_cpu_stall_init(void)
 {
 }

diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index bb4d08695c4568a095014dddc9c76a1c455f3a14..7abd439a757324349ab2c4d7299017075764b8e9 100644 (file)
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -372,6 +372,7 @@ static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp,
 #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);
+static void rcu_preempt_stall_reset(void);
 #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
 static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp);
 #ifdef CONFIG_HOTPLUG_CPU

diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 63bb7714fdebdf74dddd2f5febb1bfbc56b9080b..561410f70d4a507723c939f568c1cc9adf2204d6 100644 (file)
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -417,6 +417,16 @@ static void rcu_print_task_stall(struct rcu_node *rnp)
        }
 }
 
+/*
+ * Suppress preemptible RCU's CPU stall warnings by pushing the
+ * time of the next stall-warning message comfortably far into the
+ * future.
+ */
+static void rcu_preempt_stall_reset(void)
+{
+       rcu_preempt_state.jiffies_stall = jiffies + ULONG_MAX / 2;
+}
+
 #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
 
 /*
@@ -867,6 +877,14 @@ static void rcu_print_task_stall(struct rcu_node *rnp)
 {
 }
 
+/*
+ * Because preemptible RCU does not exist, there is no need to suppress
+ * its CPU stall warnings.
+ */
+static void rcu_preempt_stall_reset(void)
+{
+}
+
 #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
 
 /*