kernel/rcu/tree_stall: add /sys/kernel/rcu_stall_count

Expose a simple counter to userspace for monitoring tools.

(akpm: 2536c5c7d6ae added the documentation but the code changes were lost)

Link: https://lkml.kernel.org/r/20250504180831.4190860-3-max.kellermann@ionos.com
Fixes: 2536c5c7d6ae ("kernel/rcu/tree_stall: add /sys/kernel/rcu_stall_count")
Signed-off-by: Max Kellermann <max.kellermann@ionos.com>
Cc: Core Minyard <cminyard@mvista.com>
Cc: Doug Anderson <dianders@chromium.org>
Cc: Joel Granados <joel.granados@kernel.org>
Cc: Max Kellermann <max.kellermann@ionos.com>
Cc: Song Liu <song@kernel.org>
Cc: Sourabh Jain <sourabhjain@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index 56b21219442b65d4e37765ef802353c0fc6f9bfc..486c00536207d58a621ee97cf2e83834cdb186aa 100644 (file)
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -20,6 +20,28 @@
 int sysctl_panic_on_rcu_stall __read_mostly;
 int sysctl_max_rcu_stall_to_panic __read_mostly;
 
+#ifdef CONFIG_SYSFS
+
+static unsigned int rcu_stall_count;
+
+static ssize_t rcu_stall_count_show(struct kobject *kobj, struct kobj_attribute *attr,
+                                   char *page)
+{
+       return sysfs_emit(page, "%u\n", rcu_stall_count);
+}
+
+static struct kobj_attribute rcu_stall_count_attr = __ATTR_RO(rcu_stall_count);
+
+static __init int kernel_rcu_stall_sysfs_init(void)
+{
+       sysfs_add_file_to_group(kernel_kobj, &rcu_stall_count_attr.attr, NULL);
+       return 0;
+}
+
+late_initcall(kernel_rcu_stall_sysfs_init);
+
+#endif // CONFIG_SYSFS
+
 #ifdef CONFIG_PROVE_RCU
 #define RCU_STALL_DELAY_DELTA          (5 * HZ)
 #else
@@ -784,6 +806,10 @@ static void check_cpu_stall(struct rcu_data *rdp)
                if (kvm_check_and_clear_guest_paused())
                        return;
 
+#ifdef CONFIG_SYSFS
+               ++rcu_stall_count;
+#endif
+
                rcu_stall_notifier_call_chain(RCU_STALL_NOTIFY_NORM, (void *)j - gps);
                if (READ_ONCE(csd_lock_suppress_rcu_stall) && csd_lock_is_stuck()) {
                        pr_err("INFO: %s detected stall, but suppressed full report due to a stuck CSD-lock.\n", rcu_state.name);