linux-kernel - [PATCH 4/5] kernel/watchdog_hld: simplify the detecting of hld watchdog

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Date:   Wed, 15 Sep 2021 11:51:02 +0800
From:   Pingfan Liu <kernelfans@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Pingfan Liu <kernelfans@...il.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>
Subject: [PATCH 4/5] kernel/watchdog_hld: simplify the detecting of hld watchdog

By utilizing the new interface model, the stages of probe and enable can
be merged, which saves the pair of perf_event alloc and free.

Signed-off-by: Pingfan Liu <kernelfans@...il.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>
To: linux-kernel@...r.kernel.org
---
 include/linux/nmi.h   |  8 ++------
 kernel/watchdog.c     | 16 ++++++++++++++--
 kernel/watchdog_hld.c | 21 +++------------------
 3 files changed, 19 insertions(+), 26 deletions(-)

diff --git a/include/linux/nmi.h b/include/linux/nmi.h
index 70665fa6e0a9..e41cdf3edba7 100644
--- a/include/linux/nmi.h
+++ b/include/linux/nmi.h
@@ -101,20 +101,16 @@ extern void arch_touch_nmi_watchdog(void);
 extern void hardlockup_detector_perf_stop(void);
 extern void hardlockup_detector_perf_restart(void);
 extern void hardlockup_detector_perf_disable(void);
-extern void hardlockup_detector_perf_enable(void);
+extern int hardlockup_detector_perf_enable(void);
 extern void hardlockup_detector_perf_cleanup(void);
-extern int hardlockup_detector_perf_init(void);
 #else
 static inline void hardlockup_detector_perf_stop(void) { }
 static inline void hardlockup_detector_perf_restart(void) { }
 static inline void hardlockup_detector_perf_disable(void) { }
-static inline void hardlockup_detector_perf_enable(void) { }
+static inline int hardlockup_detector_perf_enable(void) { return -ENODEV; }
 static inline void hardlockup_detector_perf_cleanup(void) { }
 # if !defined(CONFIG_HAVE_NMI_WATCHDOG)
-static inline int hardlockup_detector_perf_init(void) { return -ENODEV; }
 static inline void arch_touch_nmi_watchdog(void) {}
-# else
-static inline int hardlockup_detector_perf_init(void) { return 0; }
 # endif
 #endif
 
diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 4ab71943d65f..3f5efbd5961c 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -99,7 +99,17 @@ static watchdog_nmi_status_reporter status_reporter;
  */
 void __weak watchdog_nmi_enable(unsigned int cpu)
 {
-	hardlockup_detector_perf_enable();
+	struct watchdog_nmi_status data;
+	int ret;
+
+	ret = hardlockup_detector_perf_enable();
+	/* No concurrent risk because BP executes this before smp_init() */
+	if (watchdog_enabled & NMI_WATCHDOG_UNDETERMINED
+			&& status_reporter) {
+		data.cpu = cpu;
+		data.status = ret;
+		(*status_reporter)(&data);
+	}
 }
 
 void __weak watchdog_nmi_disable(unsigned int cpu)
@@ -130,7 +140,9 @@ static void watchdog_nmi_report_capability(struct watchdog_nmi_status *data)
  */
 int __weak __init watchdog_nmi_probe(watchdog_nmi_status_reporter notifier)
 {
-	return hardlockup_detector_perf_init();
+	status_reporter = notifier;
+
+	return -EBUSY;
 }
 
 /**
diff --git a/kernel/watchdog_hld.c b/kernel/watchdog_hld.c
index 6876e796dbf5..2894778fbc6d 100644
--- a/kernel/watchdog_hld.c
+++ b/kernel/watchdog_hld.c
@@ -190,16 +190,17 @@ static int hardlockup_detector_event_create(void)
 /**
  * hardlockup_detector_perf_enable - Enable the local event
  */
-void hardlockup_detector_perf_enable(void)
+int hardlockup_detector_perf_enable(void)
 {
 	if (hardlockup_detector_event_create())
-		return;
+		return -ENODEV;
 
 	/* use original value for check */
 	if (!atomic_fetch_inc(&watchdog_cpus))
 		pr_info("Enabled. Permanently consumes one hw-PMU counter.\n");
 
 	perf_event_enable(this_cpu_read(watchdog_ev));
+	return 0;
 }
 
 /**
@@ -281,19 +282,3 @@ void __init hardlockup_detector_perf_restart(void)
 			perf_event_enable(event);
 	}
 }
-
-/**
- * hardlockup_detector_perf_init - Probe whether NMI event is available at all
- */
-int __init hardlockup_detector_perf_init(void)
-{
-	int ret = hardlockup_detector_event_create();
-
-	if (ret) {
-		pr_info("Perf NMI watchdog permanently disabled\n");
-	} else {
-		perf_event_release_kernel(this_cpu_read(watchdog_ev));
-		this_cpu_write(watchdog_ev, NULL);
-	}
-	return ret;
-}
-- 
2.31.1