linux-kernel - [PATCHv2 3/4] kernel/watchdog: adapt the watchdog

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Date:   Thu, 23 Sep 2021 22:09:50 +0800
From:   Pingfan Liu <kernelfans@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Pingfan Liu <kernelfans@...il.com>,
        Sumit Garg <sumit.garg@...aro.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Marc Zyngier <maz@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Petr Mladek <pmladek@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Wang Qing <wangqing@...o.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Santosh Sivaraj <santosh@...six.org>,
        linux-arm-kernel@...ts.infradead.org
Subject: [PATCHv2 3/4] kernel/watchdog: adapt the watchdog_hld interface for async model

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 by enabling watchdog_hld to
get the capability of PMU async.

The async model is achieved by expanding watchdog_nmi_probe() with
-EBUSY, and a re-initializing work_struct which waits on a wait_queue_head.

Signed-off-by: Pingfan Liu <kernelfans@...il.com>
Cc: Sumit Garg <sumit.garg@...aro.org>
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Will Deacon <will@...nel.org>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: Mark Rutland <mark.rutland@....com>
Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Marc Zyngier <maz@...nel.org>
Cc: Kees Cook <keescook@...omium.org>
Cc: Masahiro Yamada <masahiroy@...nel.org>
Cc: Sami Tolvanen <samitolvanen@...gle.com>
Cc: Petr Mladek <pmladek@...e.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Wang Qing <wangqing@...o.com>
Cc: "Peter Zijlstra (Intel)" <peterz@...radead.org>
Cc: Santosh Sivaraj <santosh@...six.org>
Cc: linux-arm-kernel@...ts.infradead.org
To: linux-kernel@...r.kernel.org
---
 include/linux/nmi.h |  3 +++
 kernel/watchdog.c   | 37 +++++++++++++++++++++++++++++++++++--
 2 files changed, 38 insertions(+), 2 deletions(-)

diff --git a/include/linux/nmi.h b/include/linux/nmi.h
index b7bcd63c36b4..270d440fe4b7 100644
--- a/include/linux/nmi.h
+++ b/include/linux/nmi.h
@@ -118,6 +118,9 @@ static inline int hardlockup_detector_perf_init(void) { return 0; }
 
 void watchdog_nmi_stop(void);
 void watchdog_nmi_start(void);
+
+extern bool hld_detector_delay_initialized;
+extern struct wait_queue_head hld_detector_wait;
 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 6e6dd5f0bc3e..bd4ae1839b72 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -103,7 +103,10 @@ void __weak watchdog_nmi_disable(unsigned int cpu)
 	hardlockup_detector_perf_disable();
 }
 
-/* Return 0, if a NMI watchdog is available. Error code otherwise */
+/*
+ * Return 0, if a NMI watchdog is available. -EBUSY if not ready.
+ * Other negative value if not support.
+ */
 int __weak __init watchdog_nmi_probe(void)
 {
 	return hardlockup_detector_perf_init();
@@ -739,15 +742,45 @@ int proc_watchdog_cpumask(struct ctl_table *table, int write,
 }
 #endif /* CONFIG_SYSCTL */
 
+static void lockup_detector_delay_init(struct work_struct *work);
+bool hld_detector_delay_initialized __initdata;
+
+struct wait_queue_head hld_detector_wait __initdata =
+		__WAIT_QUEUE_HEAD_INITIALIZER(hld_detector_wait);
+
+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;
+
+	wait_event(hld_detector_wait, hld_detector_delay_initialized);
+	ret = watchdog_nmi_probe();
+	if (!ret) {
+		nmi_watchdog_available = true;
+		lockup_detector_setup();
+	} else {
+		WARN_ON(ret == -EBUSY);
+		pr_info("Perf NMI watchdog permanently disabled\n");
+	}
+}
+
 void __init lockup_detector_init(void)
 {
+	int ret;
+
 	if (tick_nohz_full_enabled())
 		pr_info("Disabling watchdog on nohz_full cores by default\n");
 
 	cpumask_copy(&watchdog_cpumask,
 		     housekeeping_cpumask(HK_FLAG_TIMER));
 
-	if (!watchdog_nmi_probe())
+	ret = watchdog_nmi_probe();
+	if (!ret)
 		nmi_watchdog_available = true;
+	else if (ret == -EBUSY)
+		queue_work_on(smp_processor_id(), system_wq, &detector_work);
+
 	lockup_detector_setup();
 }
-- 
2.31.1