Commit aaf05e96 authored by Max Kellermann's avatar Max Kellermann Committed by Andrew Morton
Browse files

kernel/watchdog: add /sys/kernel/{hard,soft}lockup_count 

Patch series "sysfs: add counters for lockups and stalls", v2.

Commits 9db89b41 ("exit: Expose "oops_count" to sysfs") and
8b05aa26 ("panic: Expose "warn_count" to sysfs") added counters for
oopses and warnings to sysfs, and these two patches do the same for
hard/soft lockups and RCU stalls.

All of these counters are useful for monitoring tools to detect whether
the machine is healthy.  If the kernel has experienced a lockup or a
stall, it's probably due to a kernel bug, and I'd like to detect that
quickly and easily.  There is currently no way to detect that, other than
parsing dmesg.  Or observing indirect effects: such as certain tasks not
responding, but then I need to observe all tasks, and it may take a while
until these effects become visible/measurable.  I'd rather be able to
detect the primary cause more quickly, possibly before everything falls
apart.


This patch (of 2):

There is /proc/sys/kernel/hung_task_detect_count, /sys/kernel/warn_count
and /sys/kernel/oops_count but there is no userspace-accessible counter
for hard/soft lockups.  Having this is useful for monitoring tools.

Link: https://lkml.kernel.org/r/20250504180831.4190860-1-max.kellermann@ionos.com
Link: https://lkml.kernel.org/r/20250504180831.4190860-2-max.kellermann@ionos.com


Signed-off-by: default avatarMax Kellermann <max.kellermann@ionos.com>
Cc:
Cc: Core Minyard <cminyard@mvista.com>
Cc: Doug Anderson <dianders@chromium.org>
Cc: Joel Granados <joel.granados@kernel.org>
Cc: Song Liu <song@kernel.org>
Cc: Kees Cook <kees@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent cc66e486

Documentation/ABI/testing/sysfs-kernel-hardlockup_count

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+7 −0
Original line number Diff line number Diff line 
What:		/sys/kernel/hardlockup_count

Date:		May 2025

KernelVersion:	6.16

Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>

Description:

		Shows how many times the system has detected a hard lockup since last boot.

		Available only if CONFIG_HARDLOCKUP_DETECTOR is enabled.

Documentation/ABI/testing/sysfs-kernel-softlockup_count

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+7 −0
Original line number Diff line number Diff line 
What:		/sys/kernel/softlockup_count

Date:		May 2025

KernelVersion:	6.16

Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>

Description:

		Shows how many times the system has detected a soft lockup since last boot.

		Available only if CONFIG_SOFTLOCKUP_DETECTOR is enabled.

kernel/watchdog.c

+53 −0
Original line number Diff line number Diff line
@@ -64,6 +64,29 @@ int __read_mostly sysctl_hardlockup_all_cpu_backtrace; 
 */

unsigned int __read_mostly hardlockup_panic =

			IS_ENABLED(CONFIG_BOOTPARAM_HARDLOCKUP_PANIC);



#ifdef CONFIG_SYSFS



static unsigned int hardlockup_count;



static ssize_t hardlockup_count_show(struct kobject *kobj, struct kobj_attribute *attr,

				     char *page)

{

	return sysfs_emit(page, "%u\n", hardlockup_count);

}



static struct kobj_attribute hardlockup_count_attr = __ATTR_RO(hardlockup_count);



static __init int kernel_hardlockup_sysfs_init(void)

{

	sysfs_add_file_to_group(kernel_kobj, &hardlockup_count_attr.attr, NULL);

	return 0;

}



late_initcall(kernel_hardlockup_sysfs_init);



#endif // CONFIG_SYSFS



/*

 * We may not want to enable hard lockup detection by default in all cases,

 * for example when running the kernel as a guest on a hypervisor. In these
@@ -170,6 +193,10 @@ void watchdog_hardlockup_check(unsigned int cpu, struct pt_regs *regs) 
		unsigned int this_cpu = smp_processor_id();

		unsigned long flags;



#ifdef CONFIG_SYSFS

		++hardlockup_count;

#endif



		/* Only print hardlockups once. */

		if (per_cpu(watchdog_hardlockup_warned, cpu))

			return;
@@ -312,6 +339,28 @@ unsigned int __read_mostly softlockup_panic = 
static bool softlockup_initialized __read_mostly;

static u64 __read_mostly sample_period;



#ifdef CONFIG_SYSFS



static unsigned int softlockup_count;



static ssize_t softlockup_count_show(struct kobject *kobj, struct kobj_attribute *attr,

				     char *page)

{

	return sysfs_emit(page, "%u\n", softlockup_count);

}



static struct kobj_attribute softlockup_count_attr = __ATTR_RO(softlockup_count);



static __init int kernel_softlockup_sysfs_init(void)

{

	sysfs_add_file_to_group(kernel_kobj, &softlockup_count_attr.attr, NULL);

	return 0;

}



late_initcall(kernel_softlockup_sysfs_init);



#endif // CONFIG_SYSFS



/* Timestamp taken after the last successful reschedule. */

static DEFINE_PER_CPU(unsigned long, watchdog_touch_ts);

/* Timestamp of the last softlockup report. */
@@ -743,6 +792,10 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer) 
	touch_ts = __this_cpu_read(watchdog_touch_ts);

	duration = is_softlockup(touch_ts, period_ts, now);

	if (unlikely(duration)) {

#ifdef CONFIG_SYSFS

		++softlockup_count;

#endif



		/*

		 * Prevent multiple soft-lockup reports if one cpu is already

		 * engaged in dumping all cpu back traces.