diff mbox series

[v4,4/6] kernel/watchdog: Adapt the watchdog_hld interface for async model

Message ID 20220427161340.8518-5-lecopzer.chen@mediatek.com (mailing list archive)
State New, archived
Headers show
Series Support hld delayed init based on Pseudo-NMI for arm64 | expand

Commit Message

Lecopzer Chen April 27, 2022, 4:13 p.m. UTC 
When lockup_detector_init()->watchdog_nmi_probe(), PMU may be not ready
yet. E.g. on arm64, PMU is not ready until
device_initcall(armv8_pmu_driver_init).  And it is deeply integrated
with the driver model and cpuhp. Hence it is hard to push this
initialization before smp_init().

But it is easy to take an opposite approach and try to initialize
the watchdog once again later.
The delayed probe is called using workqueues. It need to allocate
memory and must be proceed in a normal context.
The delayed probe is able to use if watchdog_nmi_probe() returns
non-zero which means the return code returned when PMU is not ready yet.

Provide an API - retry_lockup_detector_init() for anyone who needs
to delayed init lockup detector if they had ever failed at
lockup_detector_init().

The original assumption is: nobody should use delayed probe after
lockup_detector_check() which has __init attribute.
That is, anyone uses this API must call between lockup_detector_init()
and lockup_detector_check(), and the caller must have __init attribute

Co-developed-by: Pingfan Liu <kernelfans@gmail.com>
Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
Signed-off-by: Lecopzer Chen <lecopzer.chen@mediatek.com>
Suggested-by: Petr Mladek <pmladek@suse.com>
---
 include/linux/nmi.h |  2 ++
 kernel/watchdog.c   | 67 ++++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 68 insertions(+), 1 deletion(-)

Comments

Petr Mladek May 20, 2022, 9:38 a.m. UTC | #1 
On Thu 2022-04-28 00:13:38, Lecopzer Chen wrote:
> When lockup_detector_init()->watchdog_nmi_probe(), PMU may be not ready
> yet. E.g. on arm64, PMU is not ready until
> device_initcall(armv8_pmu_driver_init).  And it is deeply integrated
> with the driver model and cpuhp. Hence it is hard to push this
> initialization before smp_init().
> 
> But it is easy to take an opposite approach and try to initialize
> the watchdog once again later.
> The delayed probe is called using workqueues. It need to allocate
> memory and must be proceed in a normal context.
> The delayed probe is able to use if watchdog_nmi_probe() returns
> non-zero which means the return code returned when PMU is not ready yet.
> 
> Provide an API - retry_lockup_detector_init() for anyone who needs
> to delayed init lockup detector if they had ever failed at
> lockup_detector_init().
> 
> The original assumption is: nobody should use delayed probe after
> lockup_detector_check() which has __init attribute.
> That is, anyone uses this API must call between lockup_detector_init()
> and lockup_detector_check(), and the caller must have __init attribute
> 
> --- a/kernel/watchdog.c
> +++ b/kernel/watchdog.c
> +/*
> + * retry_lockup_detector_init - retry init lockup detector if possible.
> + *
> + * Retry hardlockup detector init. It is useful when it requires some
> + * functionality that has to be initialized later on a particular
> + * platform.
> + */
> +void __init retry_lockup_detector_init(void)
> +{
> +	/* Must be called before late init calls */
> +	if (!allow_lockup_detector_init_retry)
> +		return;
> +
> +	queue_work_on(__smp_processor_id(), system_wq, &detector_work);

Just a small nit. This can be simplified by calling:

	schedule_work(&detector_work);

It uses "system_wq" that uses CPU-bound workers. It prefers
the current CPU. But the exact CPU is not important. Any CPU-bound
worker is enough.

> +}
> +

With the above change, feel free to use:

Reviewed-by: Petr Mladek <pmladek@suse.com>

Best Regards,
Petr

PS: I am sorry for the late review. I had busy weeks.
Lecopzer Chen May 26, 2022, 9:39 a.m. UTC | #2 
> On Thu 2022-04-28 00:13:38, Lecopzer Chen wrote:
> > When lockup_detector_init()->watchdog_nmi_probe(), PMU may be not ready
> > yet. E.g. on arm64, PMU is not ready until
> > device_initcall(armv8_pmu_driver_init).  And it is deeply integrated
> > with the driver model and cpuhp. Hence it is hard to push this
> > initialization before smp_init().
> > 
> > But it is easy to take an opposite approach and try to initialize
> > the watchdog once again later.
> > The delayed probe is called using workqueues. It need to allocate
> > memory and must be proceed in a normal context.
> > The delayed probe is able to use if watchdog_nmi_probe() returns
> > non-zero which means the return code returned when PMU is not ready yet.
> > 
> > Provide an API - retry_lockup_detector_init() for anyone who needs
> > to delayed init lockup detector if they had ever failed at
> > lockup_detector_init().
> > 
> > The original assumption is: nobody should use delayed probe after
> > lockup_detector_check() which has __init attribute.
> > That is, anyone uses this API must call between lockup_detector_init()
> > and lockup_detector_check(), and the caller must have __init attribute
> > 
> > --- a/kernel/watchdog.c
> > +++ b/kernel/watchdog.c
> > +/*
> > + * retry_lockup_detector_init - retry init lockup detector if possible.
> > + *
> > + * Retry hardlockup detector init. It is useful when it requires some
> > + * functionality that has to be initialized later on a particular
> > + * platform.
> > + */
> > +void __init retry_lockup_detector_init(void)
> > +{
> > +	/* Must be called before late init calls */
> > +	if (!allow_lockup_detector_init_retry)
> > +		return;
> > +
> > +	queue_work_on(__smp_processor_id(), system_wq, &detector_work);
> 
> Just a small nit. This can be simplified by calling:
> 
> 	schedule_work(&detector_work);
> 
> It uses "system_wq" that uses CPU-bound workers. It prefers
> the current CPU. But the exact CPU is not important. Any CPU-bound
> worker is enough.

Thanks!! I'll tweak this on -rc1
> 
> > +}
> > +
> 
> With the above change, feel free to use:
> 
> Reviewed-by: Petr Mladek <pmladek@suse.com>

Really appreciate your review and idea, thank you ver much.


BRs,
Lecopzer
diff mbox series

Patch

diff --git a/include/linux/nmi.h b/include/linux/nmi.h
index b7bcd63c36b4..10f2a305fe0d 100644
--- a/include/linux/nmi.h
+++ b/include/linux/nmi.h
@@ -118,6 +118,8 @@  static inline int hardlockup_detector_perf_init(void) { return 0; }
 
 void watchdog_nmi_stop(void);
 void watchdog_nmi_start(void);
+
+void retry_lockup_detector_init(void);
 int watchdog_nmi_probe(void);
 void watchdog_nmi_enable(unsigned int cpu);
 void watchdog_nmi_disable(unsigned int cpu);
diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index ca85ca5fdeff..1edc23af3b80 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -103,7 +103,13 @@  void __weak watchdog_nmi_disable(unsigned int cpu)
 	hardlockup_detector_perf_disable();
 }
 
-/* Return 0, if a NMI watchdog is available. Error code otherwise */
+/*
+ * Arch specific API.
+ *
+ * Return 0 when NMI watchdog is available, negative value otherwise.
+ * Note that the negative value means that a delayed probe might
+ * succeed later.
+ */
 int __weak __init watchdog_nmi_probe(void)
 {
 	return hardlockup_detector_perf_init();
@@ -831,6 +837,62 @@  static struct ctl_table watchdog_sysctls[] = {
 	{}
 };
 
+static void __init lockup_detector_delay_init(struct work_struct *work);
+static bool allow_lockup_detector_init_retry __initdata;
+
+static struct work_struct detector_work __initdata =
+		__WORK_INITIALIZER(detector_work, lockup_detector_delay_init);
+
+static void __init lockup_detector_delay_init(struct work_struct *work)
+{
+	int ret;
+
+	ret = watchdog_nmi_probe();
+	if (ret) {
+		pr_info("Delayed init of the lockup detector failed: %d\n", ret);
+		pr_info("Perf NMI watchdog permanently disabled\n");
+		return;
+	}
+
+	allow_lockup_detector_init_retry = false;
+
+	nmi_watchdog_available = true;
+	lockup_detector_setup();
+}
+
+/*
+ * retry_lockup_detector_init - retry init lockup detector if possible.
+ *
+ * Retry hardlockup detector init. It is useful when it requires some
+ * functionality that has to be initialized later on a particular
+ * platform.
+ */
+void __init retry_lockup_detector_init(void)
+{
+	/* Must be called before late init calls */
+	if (!allow_lockup_detector_init_retry)
+		return;
+
+	queue_work_on(__smp_processor_id(), system_wq, &detector_work);
+}
+
+/*
+ * Ensure that optional delayed hardlockup init is proceed before
+ * the init code and memory is freed.
+ */
+static int __init lockup_detector_check(void)
+{
+	/* Prevent any later retry. */
+	allow_lockup_detector_init_retry = false;
+
+	/* Make sure no work is pending. */
+	flush_work(&detector_work);
+
+	return 0;
+
+}
+late_initcall_sync(lockup_detector_check);
+
 static void __init watchdog_sysctl_init(void)
 {
 	register_sysctl_init("kernel", watchdog_sysctls);
@@ -849,6 +911,9 @@  void __init lockup_detector_init(void)
 
 	if (!watchdog_nmi_probe())
 		nmi_watchdog_available = true;
+	else
+		allow_lockup_detector_init_retry = true;
+
 	lockup_detector_setup();
 	watchdog_sysctl_init();
 }