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Thu, 23 Sep 2021 07:10:27 -0700 (PDT) From: Pingfan Liu To: linux-kernel@vger.kernel.org Cc: Pingfan Liu , Petr Mladek , Andrew Morton , Wang Qing , "Peter Zijlstra (Intel)" , Santosh Sivaraj , linux-arm-kernel@lists.infradead.org Subject: [PATCHv2 2/4] kernel/watchdog_hld: clarify the condition in hardlockup_detector_event_create() Date: Thu, 23 Sep 2021 22:09:49 +0800 Message-Id: <20210923140951.35902-3-kernelfans@gmail.com> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20210923140951.35902-1-kernelfans@gmail.com> References: <20210923140951.35902-1-kernelfans@gmail.com> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210923_071029_098063_A9082099 X-CRM114-Status: GOOD ( 15.09 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org As for the context, there are two arguments to change debug_smp_processor_id() to is_percpu_thread(). -1. watchdog_ev is percpu, and migration will frustrate the attempt which try to bind a watchdog_ev to a cpu by protecting this func inside the pair of preempt_disable()/preempt_enable(). -2. hardlockup_detector_event_create() indirectly calls kmem_cache_alloc_node(), which is blockable. So here, spelling out the really planned context "is_percpu_thread()". Signed-off-by: Pingfan Liu Cc: Petr Mladek Cc: Andrew Morton Cc: Wang Qing Cc: "Peter Zijlstra (Intel)" Cc: Santosh Sivaraj Cc: linux-arm-kernel@lists.infradead.org To: linux-kernel@vger.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);