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([2601:188:c102:b180:1f8b:71d0:77b1:1f6e]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-8942e6040casm134934466d6.21.2026.01.21.08.48.41 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 21 Jan 2026 08:48:42 -0800 (PST) From: Waiman Long X-Google-Original-From: Waiman Long Message-ID: <0bada1e3-f312-4b72-974c-4b061e577d66@redhat.com> Date: Wed, 21 Jan 2026 11:48:41 -0500 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] irqchip/gic-v3-its: Don't acquire rt_spin_lock in allocate_vpe_l1_table() To: Marc Zyngier , Thomas Gleixner Cc: Sebastian Andrzej Siewior , Clark Williams , Steven Rostedt , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev References: <20260107215353.75612-1-longman@redhat.com> <864iowmrx6.wl-maz@kernel.org> <87ms2nsqju.ffs@tglx> <86wm1qlq7l.wl-maz@kernel.org> <87ecnwij44.ffs@tglx> <86v7h8l9ht.wl-maz@kernel.org> <87pl7gglya.ffs@tglx> <86tswrkrh4.wl-maz@kernel.org> <861pjjcqdi.wl-maz@kernel.org> Content-Language: en-US In-Reply-To: <861pjjcqdi.wl-maz@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 1/21/26 3:38 AM, Marc Zyngier wrote: > On Mon, 12 Jan 2026 11:20:07 +0000, > Marc Zyngier wrote: >> On Sun, 11 Jan 2026 16:20:45 +0000, >> Thomas Gleixner wrote: >>> On Sun, Jan 11 2026 at 10:38, Marc Zyngier wrote: >>>> On Sun, 11 Jan 2026 09:39:07 +0000, >>>> Thomas Gleixner wrote: >>>>> On Fri, Jan 09 2026 at 16:13, Marc Zyngier wrote: >>>>>> On Thu, 08 Jan 2026 22:11:33 +0000, >>>>>> Thomas Gleixner wrote: >>>>>>> At the point where a CPU is brought up, the topology should be known >>>>>>> already, which means this can be allocated on the control CPU _before_ >>>>>>> the new CPU comes up, no? >>>>>> No. Each CPU finds *itself* in the forest of redistributors, and from >>>>>> there tries to find whether it has some shared resource with a CPU >>>>>> that has booted before it. That's because firmware is absolutely awful >>>>>> and can't present a consistent view of the system. >>>>> Groan.... >>>>> >>>>>> Anyway, I expect it could be solved by moving this part of the init to >>>>>> an ONLINE HP callback. >>>>> Which needs to be before CPUHP_AP_IRQ_AFFINITY_ONLINE, but even that >>>>> might be to late because there are callbacks in the STARTING section, >>>>> i.e. timer, perf, which might rely on interrupts being accessible. >>>> Nah. This stuff is only for direct injection of vLPIs into guests, so >>>> as long as this is done before we can schedule a vcpu on this physical >>>> CPU, we're good. No physical interrupt is concerned with this code. >>> That's fine then. vCPUs are considered "user-space" tasks and can't be >>> scheduled before CPUHP_AP_ACTIVE sets the CPU active for the scheduler. >> Waiman, can you please give the following hack a go on your box? The >> machines I have are thankfully limited to a single ITS group, so I >> can't directly reproduce your issue. > Have you managed to try this hack? I may be able to spend some time > addressing the issue in the next cycle if I have an indication that > I'm on the right track. I am sorry that I was busy working on other stuff. Will try out the hack today and report back ASAP. Cheers, Longman