+ kernel-rcu-tree_stall-add-sys-kernel-rcu_stall_count.patch added to mm-hotfixes-unstable branch

+ kernel-rcu-tree_stall-add-sys-kernel-rcu_stall_count.patch added to mm-hotfixes-unstable branch

[Andrew Morton]

The patch titled
     Subject: kernel/rcu/tree_stall: add /sys/kernel/rcu_stall_count
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     kernel-rcu-tree_stall-add-sys-kernel-rcu_stall_count.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/kernel-rcu-tree_stall-add-sys-kernel-rcu_stall_count.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Max Kellermann <max.kellermann@ionos.com>
Subject: kernel/rcu/tree_stall: add /sys/kernel/rcu_stall_count
Date: Sun, 4 May 2025 20:08:31 +0200

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>
---

 kernel/rcu/tree_stall.h |   26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-kernel-rcu_stall_count a/Documentation/ABI/testing/sysfs-kernel-rcu_stall_count
old mode 100664
new mode 100644
--- a/kernel/rcu/tree_stall.h~kernel-rcu-tree_stall-add-sys-kernel-rcu_stall_count
+++ a/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_d
 		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);
_

Patches currently in -mm which might be from max.kellermann@ionos.com are

kernel-rcu-tree_stall-add-sys-kernel-rcu_stall_count.patch