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([2601:188:c102:b180:1f8b:71d0:77b1:1f6e]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-8942e5e4a3csm133070566d6.5.2026.01.21.08.37.50 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 21 Jan 2026 08:37:51 -0800 (PST) From: Waiman Long X-Google-Original-From: Waiman Long Message-ID: Date: Wed, 21 Jan 2026 11:37:49 -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: Vlastimil Babka , Sebastian Andrzej Siewior , Waiman Long Cc: Thomas Gleixner , Marc Zyngier , Clark Williams , Steven Rostedt , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev, Alexei Starovoitov 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> <40cec799-f363-4642-969b-24f5a2d56dfb@redhat.com> <87cy3eg94y.ffs@tglx> <5f4bfd8b-8699-4bef-bf49-f29965e95ca4@redhat.com> <20260113115515.98Mc29Nm@linutronix.de> <0c33bdee-6de8-4d9f-92ca-4f72c1b6fb9f@suse.cz> Content-Language: en-US In-Reply-To: <0c33bdee-6de8-4d9f-92ca-4f72c1b6fb9f@suse.cz> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 1/14/26 12:59 PM, Vlastimil Babka wrote: > On 1/13/26 12:55, Sebastian Andrzej Siewior wrote: >> On 2026-01-12 12:14:30 [-0500], Waiman Long wrote: >>> On 1/12/26 10:09 AM, Thomas Gleixner wrote: >>>> They might be acquired though. Only alloc_pages_nolock() guarantees that >>>> no lock is taken IIRC. >>> Thanks for the suggestion. I will look into using that for page allocation. >>> I had actually attempt to use kmalloc_nolock() to replace kzalloc() >>> initially. Even though it removed the call to rmqueue(), but there were >>> other spinlocks in the slub code that were still being acquired like the >>> local_lock() or the spinlock in the get_random() code. So I gave up using > Hmm if get_random() code takes a spinlock, we have an unsolved > incompatibility with kmalloc_nolock() and CONFIG_SLAB_FREELIST_RANDOM. > >>> that. Anyway, kmalloc_nolock() doesn't seem to be fully working yet. >> with kmalloc_nolock() you have to be able to deal with a NULL pointer. > Yes. So even after we fix the current problems with incompatible context, I > think kmalloc_nolock() would still be a bad fit for hw bringup code that > should not really fail. Because the possibility of failure will always > exist. The BPF use case that motivated it is quite different. Yes, it is an issue too that kmalloc_nolock() may fail. If that happens, we don't have another good alternative. Cheers, Longman