[PATCH v6 3/6] kernel/watchdog_hld: Ensure CPU-bound context when creating hardlockup detector event

From: Lecopzer Chen <lecopzer.chen@mediatek.com>
To: <linux-arm-kernel@lists.infradead.org>, <linux-kernel@vger.kernel.org>
Cc: <pmladek@suse.com>, <acme@kernel.org>,
	<akpm@linux-foundation.org>, <alexander.shishkin@linux.intel.com>,
	<catalin.marinas@arm.com>, <davem@davemloft.net>,
	<jolsa@redhat.com>, <jthierry@redhat.com>,
	<keescook@chromium.org>, <kernelfans@gmail.com>,
	<lecopzer.chen@mediatek.com>,
	<linux-mediatek@lists.infradead.org>,
	<linux-perf-users@vger.kernel.org>, <mark.rutland@arm.com>,
	<masahiroy@kernel.org>, <matthias.bgg@gmail.com>,
	<maz@kernel.org>, <mcgrof@kernel.org>, <mingo@redhat.com>,
	<namhyung@kernel.org>, <nixiaoming@huawei.com>,
	<peterz@infradead.org>, <sparclinux@vger.kernel.org>,
	<sumit.garg@linaro.org>, <wangqing@vivo.com>, <will@kernel.org>,
	<yj.chiang@mediatek.com>
Subject: [PATCH v6 3/6] kernel/watchdog_hld: Ensure CPU-bound context when creating hardlockup detector event
Date: Tue, 14 Jun 2022 14:28:32 +0800	[thread overview]
Message-ID: <20220614062835.7196-4-lecopzer.chen@mediatek.com> (raw)
In-Reply-To: <20220614062835.7196-1-lecopzer.chen@mediatek.com>

From: Pingfan Liu <kernelfans@gmail.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@gmail.com>
Co-developed-by: Lecopzer Chen <lecopzer.chen@mediatek.com>
Signed-off-by: Lecopzer Chen <lecopzer.chen@mediatek.com>
Reviewed-by: Petr Mladek <pmladek@suse.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 701f35f0e2d4..0573cef0b9dc 100644
--- a/kernel/watchdog_hld.c
+++ b/kernel/watchdog_hld.c
@@ -169,10 +169,16 @@ 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

