linux-kernel - [PATCHv3 2/4] kernel/watchdog_hld: Ensure CPU-bound context when creating hardlockup detector event

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Date:   Thu, 14 Oct 2021 10:41:53 +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>,
        linux-arm-kernel@...ts.infradead.org
Subject: [PATCHv3 2/4] kernel/watchdog_hld: Ensure CPU-bound context when creating hardlockup detector event

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>
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
---
 kernel/watchdog_hld.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/watchdog_hld.c b/kernel/watchdog_hld.c
index 247bf0b1582c..df010df76576 100644
--- a/kernel/watchdog_hld.c
+++ b/kernel/watchdog_hld.c
@@ -165,10 +165,13 @@ 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;
 
+	/* This function plans to execute in cpu bound 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);
 
-- 
2.31.1