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[34.228.114.98]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-530ca460a32sm20960711cf.9.2026.09.11.07.10.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 11 Sep 2026 07:10:27 -0700 (PDT) From: Josef Bacik Date: Fri, 11 Sep 2026 14:08:53 +0000 Subject: [PATCH RFC v2 15/15] rcu-tasks: Kick running holdouts through the scheduler Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260911-b4-rcu-tasks-preempt-qs-v2-15-eaaa61ed2da4@toxicpanda.com> References: <20260911-b4-rcu-tasks-preempt-qs-v2-0-eaaa61ed2da4@toxicpanda.com> In-Reply-To: <20260911-b4-rcu-tasks-preempt-qs-v2-0-eaaa61ed2da4@toxicpanda.com> To: "Paul E. McKenney" , Frederic Weisbecker , Neeraj Upadhyay , Joel Fernandes , Boqun Feng , Thomas Gleixner , Peter Zijlstra , Steven Rostedt , Masami Hiramatsu , Mark Rutland , Jiri Olsa , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , x86@kernel.org, Catalin Marinas , Will Deacon , Puranjay Mohan , Xu Kuohai Cc: Andy Lutomirski , Josh Triplett , Uladzislau Rezki , Mathieu Desnoyers , Lai Jiangshan , Zqiang , Juergen Gross , Luis Chamberlain , Ihor Solodrai , linux-kernel@vger.kernel.org, rcu@vger.kernel.org, linux-trace-kernel@vger.kernel.org, bpf@vger.kernel.org, linux-arm-kernel@lists.infradead.org, xen-devel@lists.xenproject.org, Josef Bacik X-Mailer: b4 0.15.2 X-Developer-Signature: v=1; a=openssh-sha256; t=1789135737; l=1790; i=josef@toxicpanda.com; h=from:subject:message-id; bh=K9+ZKIgsGRgsc959M4tS0rMKOB/eZlOXTQ8Ho0gK2m4=; b=U1NIU0lHAAAAAQAAADMAAAALc3NoLWVkMjU1MTkAAAAgUBr36M/n0nWN0DNbnxwzIiCZez6MG JiruuNaSCI/zXsAAAAGcGF0YXR0AAAAAAAAAAZzaGE1MTIAAABTAAAAC3NzaC1lZDI1NTE5AAAA QFxu9w6oKo935Kq6bYpzSj4sd/pud6qAfpTImYrmpDnci7BPIoYh09XWotebu7q/uE6z/VGg6k/ nk0bYtqCcqAg= X-Developer-Key: i=josef@toxicpanda.com; a=openssh; fpr=SHA256:C8kOX2QUJCMqnCX+KEeoqRAjLo9L+ELOSH2NSAJHqGA A holdout that is running on a CPU with nothing else runnable is only preempted if the tick acts on rcu_request_urgent_qs_task()'s flag, and there may be no tick. Now that a preemption outside a trampoline is a quiescent state, have check_holdout_task() call resched_cpu() on a running holdout as well, so the scheduler IPIs it and it goes through __schedule() and reports (or, if it is inside a trampoline, does not report) its own state with purely local ordering. Nothing reads a running task's rcu_tramp_nesting remotely. Only under CONFIG_RCU_TASKS_PREEMPT_QS; other architectures are unchanged. Suggested-by: Paul E. McKenney Assisted-by: LLM Signed-off-by: Josef Bacik --- kernel/rcu/tasks.h | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h index ba432bd922e2..02d2592ab7a3 100644 --- a/kernel/rcu/tasks.h +++ b/kernel/rcu/tasks.h @@ -1038,8 +1038,18 @@ static bool rcu_tasks_preempted_qs(struct task_struct *t) { return task_call_func(t, rcu_tasks_switched_out_clean, NULL); } + +/* Make a running holdout pass through __schedule() soon, tick or no tick. */ +static void rcu_tasks_kick_running(struct task_struct *t) +{ + int cpu = task_cpu(t); + + if (task_curr(t) && cpu_online(cpu)) + resched_cpu(cpu); +} #else static bool rcu_tasks_preempted_qs(struct task_struct *t) { return false; } +static void rcu_tasks_kick_running(struct task_struct *t) { } #endif /* Per-task initial processing. */ @@ -1219,6 +1229,7 @@ static void check_holdout_task(struct task_struct *t, return; } rcu_request_urgent_qs_task(t); + rcu_tasks_kick_running(t); if (!needreport) return; if (*firstreport) { -- 2.55.0