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[2a02:3100:9c92:6501:cda9:90cd:4e49:75d9]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-48e1d8208b1sm2879816f8f.33.2026.10.19.19.14.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 19 Oct 2026 19:14:38 -0700 (PDT) Date: Tue, 20 Oct 2026 04:14:36 +0200 From: Karl Mehltretter To: Harry Yoo Cc: Peter Zijlstra , Thomas Gleixner , Sebastian Andrzej Siewior , Andrew Morton , Vlastimil Babka , Alexei Starovoitov , Ingo Molnar , Will Deacon , Boqun Feng , Waiman Long , Jonathan Corbet , David Hildenbrand , Johannes Weiner , Shakeel Butt , David Stevens , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Shuah Khan , Amery Hung , Swaraj Gaikwad , Clark Williams , Steven Rostedt , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-rt-devel@lists.linux.dev, bpf@vger.kernel.org, linux-kselftest@vger.kernel.org, cgroups@vger.kernel.org Subject: Re: [RFC PATCH v2 0/3] locking, mm: Add atomic allocator trylocks on RT Message-ID: References: <20261005070625.8871-1-kmehltretter@gmail.com> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: BF7851C0005 X-Stat-Signature: s3x971s9amwn5hzeshcudubt7c3eak1i X-Spam-Status: No, score=-2.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS autolearn=no autolearn_force=no version=4.0.1 X-Rspam-User: X-HE-Tag: 1792462480-682420 X-HE-Meta: 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 2p0ByhVG 5VIAsy+m8MEKLuZZ6DufU+rHMqCCLn2wyk/dDwwlNimE6CWzjmGCf2vL7uCfVUFr5RT/UxuTdYqzPn1gyB5/Wmg6pbFjo8ZawMQ7Yvn/hckC6i06KqFkSVbkQfD+6/2fqDOZPz+B9xRVBuTcuaP30oBY3gmbmOHS01FoXgcmPpml3jq3DCbN8MesBy5Yh8xenxl6D8vjnC93kDSRe6zzR4g2cpDls4/vcIe2zJVG86Xyx9Kc8AIUGiXeD04bUwxkoRN/RuZZgqzmB4bIIUw4sWu9bMhSZYFTQs8uQZ6voH0fdKt+E7p//KXPoI0gsqxpVvOAnltjvcFpZEeDX/JQpDiTcs/9OzUTtlv9CqSeYZJrVO/EHQVTjHwRA++oVkwysOL/LKz81tNFnajSHS57Z5YUp10A1ms/ba4M+wKa4zCiBA7hJ+fBREezyt9/4dcDoEOplib3YVZOAFkYLxh33mmVDTZGJYlKsmuTk Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Wed, Oct 07, 2026 at 07:15:29PM +0100, Harry Yoo wrote: > On Mon, Oct 05, 2026 at 09:06:22AM +0200, Karl Mehltretter wrote: > > On PREEMPT_RT, a BPF task-storage program attached to sched_waking > > can deadlock when kmalloc_nolock() obtains an rtmutex-backed allocator > > spinlock while try_to_wake_up() holds p->pi_lock. Releasing the allocator > > lock can enter priority-inheritance or wakeup code and re-enter scheduler > > locking. > > > > The first RFC [1] rejected every non-preemptible caller. That prevents the > > deadlock, but it also rejects BPF arena allocation and faults under the > > arena's ordinary raw lock. > > > > This RFC instead adds an atomic owner state for bounded PREEMPT_RT spinlock > > trylocks. Atomic acquisition succeeds only from the completely free state. > > Please don't skip discussion stage and jump into submitting a very > intrusive change across locking and mm, assisted by LLM? :/ > > I don't think attempts to tackle this problem will make progress without > discussing and getting buy-in from (PREEMPT_RT) locking folks. > Sebastian, Peter, Thomas, did you have a chance to look at the locking direction here? Thanks, Karl