[PATCH] rcu: allow multiple stalls before panic

[chao]

Some stalls are transient and system can fully recover.
Allow users to configure the number of stalls experienced
to trigger kernel Panic.

Signed-off-by: chao <chao@xxxxxxxx>
---
 include/linux/kernel.h  |  1 +
 kernel/rcu/tree_stall.h |  6 ++++++
 kernel/sysctl.c         | 11 +++++++++++
 3 files changed, 18 insertions(+)

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 500def6..fc2dd3f 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -536,6 +536,7 @@ extern int panic_on_warn;
 extern unsigned long panic_on_taint;
 extern bool panic_on_taint_nousertaint;
 extern int sysctl_panic_on_rcu_stall;
+extern int sysctl_max_rcu_stall_to_panic;
 extern int sysctl_panic_on_stackoverflow;
 
 extern bool crash_kexec_post_notifiers;
diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index b5d3b47..2047423 100644
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -13,6 +13,7 @@
 
 /* panic() on RCU Stall sysctl. */
 int sysctl_panic_on_rcu_stall __read_mostly;
+int sysctl_max_rcu_stall_to_panic __read_mostly;
 
 #ifdef CONFIG_PROVE_RCU
 #define RCU_STALL_DELAY_DELTA		(5 * HZ)
@@ -106,6 +107,11 @@ early_initcall(check_cpu_stall_init);
 /* If so specified via sysctl, panic, yielding cleaner stall-warning output. */
 static void panic_on_rcu_stall(void)
 {
+	static int cpu_stall;
+
+	if (++cpu_stall < sysctl_max_rcu_stall_to_panic)
+		return;
+
 	if (sysctl_panic_on_rcu_stall)
 		panic("RCU Stall\n");
 }
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 287862f..1bca490 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -2651,6 +2651,17 @@ static struct ctl_table kern_table[] = {
 		.extra2		= SYSCTL_ONE,
 	},
 #endif
+#if defined(CONFIG_TREE_RCU)
+	{
+		.procname	= "max_rcu_stall_to_panic",
+		.data		= &sysctl_max_rcu_stall_to_panic,
+		.maxlen		= sizeof(sysctl_max_rcu_stall_to_panic),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= SYSCTL_ONE,
+		.extra2		= SYSCTL_INT_MAX,
+	},
+#endif
 #ifdef CONFIG_STACKLEAK_RUNTIME_DISABLE
 	{
 		.procname	= "stack_erasing",
-- 
2.7.4