linux-kernel - [PATCH v2 3/5] kernel/watchdog_hld: Ensure CPU-bound context when creating hardlockup detector event

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Message-ID: <20220307154729.13477-4-lecopzer.chen@mediatek.com>
Date:   Mon, 7 Mar 2022 23:47:27 +0800
From:   Lecopzer Chen <lecopzer.chen@...iatek.com>
To:     <linux-kernel@...r.kernel.org>
CC:     <lecopzer.chen@...iatek.com>, <acme@...nel.org>,
        <akpm@...ux-foundation.org>, <alexander.shishkin@...ux.intel.com>,
        <catalin.marinas@....com>, <davem@...emloft.net>,
        <jolsa@...hat.com>, <jthierry@...hat.com>, <keescook@...omium.org>,
        <kernelfans@...il.com>, <linux-arm-kernel@...ts.infradead.org>,
        <linux-mediatek@...ts.infradead.org>,
        <linux-perf-users@...r.kernel.org>, <mark.rutland@....com>,
        <masahiroy@...nel.org>, <matthias.bgg@...il.com>, <maz@...nel.org>,
        <mcgrof@...nel.org>, <mingo@...hat.com>, <namhyung@...nel.org>,
        <nixiaoming@...wei.com>, <peterz@...radead.org>,
        <pmladek@...e.com>, <sparclinux@...r.kernel.org>,
        <sumit.garg@...aro.org>, <wangqing@...o.com>, <will@...nel.org>,
        <yj.chiang@...iatek.com>
Subject: [PATCH v2 3/5] kernel/watchdog_hld: Ensure CPU-bound context when creating hardlockup detector event

From: Pingfan Liu <kernelfans@...il.com>

hardlockup_detector_event_create() should create perf_event on the
current CPU. Preemption could not get disabled because
perf_event_create_kernel_counter() allocates memory. Instead,
the CPU locality is achieved by processing the code in a per-CPU
bound kthread.

Add a check to prevent mistakes when calling the code in another
code path.

Signed-off-by: Pingfan Liu <kernelfans@...il.com>
Co-developed-by: Lecopzer Chen <lecopzer.chen@...iatek.com>
Signed-off-by: Lecopzer Chen <lecopzer.chen@...iatek.com>
Reviewed-by: Petr Mladek <pmladek@...e.com>
---
 kernel/watchdog_hld.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/kernel/watchdog_hld.c b/kernel/watchdog_hld.c
index 247bf0b1582c..96b717205952 100644
--- a/kernel/watchdog_hld.c
+++ b/kernel/watchdog_hld.c
@@ -165,10 +165,16 @@ static void watchdog_overflow_callback(struct perf_event *event,
 
 static int hardlockup_detector_event_create(void)
 {
-	unsigned int cpu = smp_processor_id();
+	unsigned int cpu;
 	struct perf_event_attr *wd_attr;
 	struct perf_event *evt;
 
+	/*
+	 * Preemption is not disabled because memory will be allocated.
+	 * Ensure CPU-locality by calling this in per-CPU kthread.
+	 */
+	WARN_ON(!is_percpu_thread());
+	cpu = raw_smp_processor_id();
 	wd_attr = &wd_hw_attr;
 	wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);
 
-- 
2.25.1