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([2001:9e8:f12e:9401:c875:96a4:7b6f:72fd]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4922031b21dsm219645595e9.6.2026.06.15.00.16.19 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 15 Jun 2026 00:16:20 -0700 (PDT) Message-ID: Date: Mon, 15 Jun 2026 09:16:19 +0200 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] MIPS: smp: report dying CPU to RCU in stop_this_cpu() Content-Language: en-US To: Huacai Chen Cc: Thomas Bogendoerfer , linux-mips@vger.kernel.org, Sebastian Andrzej Siewior , Clark Williams , Steven Rostedt , Thomas Gleixner , Jiayuan Chen , linux-rt-devel@lists.linux.dev, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20260608093729.12111-1-jelonek.jonas@gmail.com> <731bd6c4-0f70-45a2-8480-8fed315b82b4@gmail.com> From: Jonas Jelonek In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Hi Huacai, On 15.06.26 09:09, Huacai Chen wrote: > On Mon, Jun 15, 2026 at 3:00 PM Jonas Jelonek wrote: >> Hi Huacai, >> >> sorry for the reply delay. >> >> On 10.06.26 08:05, Huacai Chen wrote: >>> [...] >>> In theory LoongArch has the same problem, but I cannot reproduce, >>> should I enable PREEMPT_RT? Or there are some special configurations? >> Sadly I cannot help with that. For MIPS, this seems to be the default >> behavior. > This patch fixes 91840be8f710, and 91840be8f710 adds synchronize_rcu() > in irq_work_sync(). Your problem is caused by this synchronize_rcu(), > right? Yes it is. > However, synchronize_rcu() only gets called in the > IS_ENABLED(CONFIG_PREEMPT_RT) case, so I think your configuration > needs PREEMPT_RT, right? > > You said this is the default behavior, but PREEMPT_RT is not enabled by default. The condition where this is added has two parts, see [1]. While PREEMPT_RT isn't active for MIPS, arch_irq_work_has_interrupt gives false for MIPS (since there is no implementation and it falls back to the generic one). This then also calls synchronize_rcu. > Huacai > Best, Jonas [1] https://elixir.bootlin.com/linux/v7.1-rc7/source/kernel/irq_work.c#L291-L302