From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B6D2230DEB2; Mon, 5 Jan 2026 15:59:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=216.40.44.11 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767628762; cv=none; b=ALD4D5jlx2g/n4vdO0uQVWaEqM3+aBJ21jQ9T6ijc7zvcERzZ5ZPYgqzyiVIMzwgjI2mk2xkIh7pWPoc/o5cJ3c5AqQTOpYySM/8HQJnnVppNKoBhNURRtRlCWi0JP5Hb+ujkvO99EyD/6OTQwztnRTV2sSA/CHOHsdY+ZCLqwE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767628762; c=relaxed/simple; bh=pXFL4t0RGtMPOBfsKIF3gef+42EspnJOjDSIdP9VCzo=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=FCl5Gpzyr+gQpXevWENCa78jNA3yj3w6NUDcPgIK2JxF+l9j8BTrK7dzceb7tWF2YUVxs+j5o33jPt7YNeGfNbwqguo5dTySxfw8rd0g+L/ODgmo7vZCT5dTQ5xMXXiYwgAdFhG2uUPsBDy5fzoOcsVCfhHQNFpeefd0CJiQft4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=goodmis.org; spf=pass smtp.mailfrom=goodmis.org; arc=none smtp.client-ip=216.40.44.11 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=goodmis.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=goodmis.org Received: from omf14.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 4910E140177; Mon, 5 Jan 2026 15:59:12 +0000 (UTC) Received: from [HIDDEN] (Authenticated sender: rostedt@goodmis.org) by omf14.hostedemail.com (Postfix) with ESMTPA id 9ECA33C; Mon, 5 Jan 2026 15:59:09 +0000 (UTC) Date: Mon, 5 Jan 2026 10:59:31 -0500 From: Steven Rostedt To: Joel Fernandes Cc: linux-kernel@vger.kernel.org, "Paul E . McKenney" , Frederic Weisbecker , Neeraj Upadhyay , Josh Triplett , Boqun Feng , Mathieu Desnoyers , Lai Jiangshan , Zqiang , Uladzislau Rezki , joel@joelfernandes.org, rcu@vger.kernel.org Subject: Re: [PATCH RFC 04/14] rcu: Promote blocked tasks from per-CPU to rnp lists Message-ID: <20260105105931.141eb6f0@gandalf.local.home> In-Reply-To: <20260103002343.6599-5-joelagnelf@nvidia.com> References: <20260103002343.6599-1-joelagnelf@nvidia.com> <20260103002343.6599-5-joelagnelf@nvidia.com> X-Mailer: Claws Mail 3.20.0git84 (GTK+ 2.24.33; x86_64-pc-linux-gnu) 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=US-ASCII Content-Transfer-Encoding: 7bit X-Stat-Signature: r4b9fmtu1qb365bwhr5zgo7yhhpdw6yg X-Rspamd-Server: rspamout04 X-Rspamd-Queue-Id: 9ECA33C X-Session-Marker: 726F737465647440676F6F646D69732E6F7267 X-Session-ID: U2FsdGVkX1/G4GO2Xjuc7QxU4HflpZpxbbLIHFKqwL8= X-HE-Tag: 1767628749-82921 X-HE-Meta: U2FsdGVkX19PEdqqCJ03quJtIe9ghdV5el7//SR/wpcJi3BYpsUGcoSC6KwNlRiz46dsUiU0rBaeiRW1yLzRCn4D9lav+VuqVhqBN7oHRDgCXmicLiZogozbAe8KhllN/Z4S11wtClG7D3ztVNTdXsj0YhPOmplQ8/qHKnVTawhi8yVc+dwuAEEIJr03zQGedffPu5pi03svciOVkJMZlawLWmWlN7S/fx4AsjSpEsIiMGwX1ERgVDgMn2+czB0DEdQJMdpwMNgq7AdPiDM/jmzNUvk1KzuZPfrC4sHyABdEvtnt7uIpTZ/9UqLBuwpv05fplaGm6JwoTFjow5Lpmkjq7SDO61It On Fri, 2 Jan 2026 19:23:33 -0500 Joel Fernandes wrote: > +#ifdef CONFIG_RCU_PER_CPU_BLOCKED_LISTS > +/* > + * Promote blocked tasks from a single CPU's per-CPU list to the rnp list. > + * > + * If there are no tracked blockers (gp_tasks NULL) and this CPU > + * is still blocking the corresponding GP (bit set in qsmask), set > + * the pointer to ensure the GP machinery knows about the blocking task. > + * This handles late promotion during QS reporting, where tasks may have > + * blocked after rcu_gp_init() or sync_exp_reset_tree() ran their scans. > + */ > +static void rcu_promote_blocked_tasks_rdp(struct rcu_data *rdp, > + struct rcu_node *rnp) > +{ > + struct task_struct *t, *tmp; > + > + raw_lockdep_assert_held_rcu_node(rnp); > + > + raw_spin_lock(&rdp->blkd_lock); > + list_for_each_entry_safe(t, tmp, &rdp->blkd_list, rcu_rdp_entry) { How big can this list be? This would be considered an unbounded latency for PREEMPT_RT. If this is needed, then we need to disable this when PREEMPT_RT is enabled. -- Steve > + /* > + * Skip tasks already on rnp list. A non-NULL > + * rcu_blocked_node indicates the task was already > + * promoted or added directly during blocking. > + * TODO: Should be WARN_ON_ONCE() after the last patch? > + */