linux-kernel - Re: [PATCH RFC 04/14] rcu: Promote blocked tasks from per-CPU to rnp lists

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20260105105931.141eb6f0@gandalf.local.home>
Date: Mon, 5 Jan 2026 10:59:31 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Joel Fernandes <joelagnelf@...dia.com>
Cc: linux-kernel@...r.kernel.org, "Paul E . McKenney" <paulmck@...nel.org>,
 Frederic Weisbecker <frederic@...nel.org>, Neeraj Upadhyay
 <neeraj.upadhyay@...nel.org>, Josh Triplett <josh@...htriplett.org>, Boqun
 Feng <boqun.feng@...il.com>, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>, Lai Jiangshan <jiangshanlai@...il.com>,
 Zqiang <qiang.zhang@...ux.dev>, Uladzislau Rezki <urezki@...il.com>,
 joel@...lfernandes.org, rcu@...r.kernel.org
Subject: Re: [PATCH RFC 04/14] rcu: Promote blocked tasks from per-CPU to
 rnp lists

On Fri,  2 Jan 2026 19:23:33 -0500
Joel Fernandes <joelagnelf@...dia.com> 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?
> +		 */