[PATCH 24/28] hazptr: Add runtime sysfs controls for stall detector

[Kunwu Chan]

Add writable sysfs attributes that let the administrator adjust
stall-detector behaviour at runtime.

Suggested-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Signed-off-by: Kunwu Chan <kunwu.chan@xxxxxxxxx>
---
 kernel/hazptr.c | 62 ++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 61 insertions(+), 1 deletion(-)

diff --git a/kernel/hazptr.c b/kernel/hazptr.c
index 7d4273a44183..66954251c332 100644
--- a/kernel/hazptr.c
+++ b/kernel/hazptr.c
@@ -423,6 +423,10 @@ static struct hazptr_scan_state hazptr_scan;
 
 /* Sysfs counters, cf. RCU's rcu_stall_count. */
 static atomic_t hazptr_stall_count = ATOMIC_INIT(0);
+#ifdef CONFIG_HAZPTR_STALL_DETECTOR
+static unsigned long hazptr_stall_timeout_ms = CONFIG_HAZPTR_STALL_TIMEOUT;
+static int hazptr_stall_suppress;
+#endif
 static atomic_t hazptr_drain_count = ATOMIC_INIT(0);
 
 #ifdef CONFIG_HAZPTR_DRAIN_ASSIST
@@ -1115,8 +1119,12 @@ static void hazptr_waiter_stall_report(struct hazptr_waiter *w)
 static void hazptr_waiter_stall_check(struct hazptr_waiter *w)
 {
 	unsigned long now = jiffies;
-	unsigned long timeout = msecs_to_jiffies(CONFIG_HAZPTR_STALL_TIMEOUT);
+	unsigned long timeout_ms = READ_ONCE(hazptr_stall_timeout_ms);
+	unsigned long timeout;
 	unsigned long deadline;
+	if (READ_ONCE(hazptr_stall_suppress) || !timeout_ms)
+		return;
+	timeout = msecs_to_jiffies(timeout_ms);
 	w->cycles++;
 	deadline = w->reports ? w->last_report + 2 * timeout
 			      : w->enqueue_jiffies + timeout;
@@ -1275,6 +1283,46 @@ void __init hazptr_init(void)
 }
 #ifdef CONFIG_SYSFS
 
+#ifdef CONFIG_HAZPTR_STALL_DETECTOR
+static ssize_t hazptr_stall_timeout_show(struct kobject *kobj,
+					  struct kobj_attribute *attr,
+					  char *page)
+{
+	return sysfs_emit(page, "%lu\n", READ_ONCE(hazptr_stall_timeout_ms));
+}
+static ssize_t hazptr_stall_timeout_store(struct kobject *kobj,
+					   struct kobj_attribute *attr,
+					   const char *buf, size_t count)
+{
+	unsigned long val;
+	int ret;
+	ret = kstrtoul(buf, 0, &val);
+	if (ret)
+		return ret;
+	if (val > 3600000)
+		return -EINVAL;
+	WRITE_ONCE(hazptr_stall_timeout_ms, val);
+	return count;
+}
+static ssize_t hazptr_stall_suppress_show(struct kobject *kobj,
+					   struct kobj_attribute *attr,
+					   char *page)
+{
+	return sysfs_emit(page, "%d\n", READ_ONCE(hazptr_stall_suppress));
+}
+static ssize_t hazptr_stall_suppress_store(struct kobject *kobj,
+					    struct kobj_attribute *attr,
+					    const char *buf, size_t count)
+{
+	int val, ret;
+	ret = kstrtoint(buf, 0, &val);
+	if (ret)
+		return ret;
+	WRITE_ONCE(hazptr_stall_suppress, !!val);
+	return count;
+}
+#endif /* CONFIG_HAZPTR_STALL_DETECTOR */
+
 static ssize_t hazptr_stall_count_show(struct kobject *kobj,
 					struct kobj_attribute *attr,
 					char *page)
@@ -1291,12 +1339,24 @@ static ssize_t hazptr_drain_count_show(struct kobject *kobj,
 static struct kobj_attribute hazptr_drain_count_attr =
 	__ATTR_RO(hazptr_drain_count);
 
+#ifdef CONFIG_HAZPTR_STALL_DETECTOR
+static struct kobj_attribute hazptr_stall_timeout_attr =
+	__ATTR(hazptr_stall_timeout_ms, 0644,
+	       hazptr_stall_timeout_show, hazptr_stall_timeout_store);
+static struct kobj_attribute hazptr_stall_suppress_attr =
+	__ATTR(hazptr_stall_suppress, 0644,
+	       hazptr_stall_suppress_show, hazptr_stall_suppress_store);
+#endif
 static struct kobj_attribute hazptr_stall_count_attr =
 	__ATTR_RO(hazptr_stall_count);
 
 static struct attribute *hazptr_sysfs_attrs[] = {
 	&hazptr_stall_count_attr.attr,
 	&hazptr_drain_count_attr.attr,
+#ifdef CONFIG_HAZPTR_STALL_DETECTOR
+	&hazptr_stall_timeout_attr.attr,
+	&hazptr_stall_suppress_attr.attr,
+#endif
 	NULL,
 };
 
-- 
2.43.0