linux-kernel - [PATCH 2/5] kernel/watchdog_hld: clarify the condition in hardlockup_detector_event

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Date:   Wed, 15 Sep 2021 11:51:00 +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>,
        Sumit Garg <sumit.garg@...aro.org>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>
Subject: [PATCH 2/5] kernel/watchdog_hld: clarify the condition in hardlockup_detector_event_create()

hardlockup_detector_event_create() indirectly calls
kmem_cache_alloc_node(), which is blockable.

So here, the really planned context is is_percpu_thread().

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: Sumit Garg <sumit.garg@...aro.org>
Cc: Will Deacon <will@...nel.org>
Cc: Mark Rutland <mark.rutland@....com>
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..6876e796dbf5 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 */
+	BUG_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