From: Paul E. McKenney <paulmck@kernel.org>
Date: Fri, 2 Aug 2024 00:34:21 +0000 (-0700)
Subject: rcu/tasks: Check processor-ID assumptions
X-Git-Tag: v6.12-rc1~166^2^6~19
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=49f49266ec9d61a4d038cb4ddff4417ba793198f;p=thirdparty%2Flinux.git

rcu/tasks: Check processor-ID assumptions

The current mapping of smp_processor_id() to a CPU processing Tasks-RCU
callbacks makes some assumptions about layout.  This commit therefore
adds a WARN_ON() to check these assumptions.

[ neeraj.upadhyay: Replace nr_cpu_ids with rcu_task_cpu_ids. ]

Signed-off-by: "Paul E. McKenney" <paulmck@kernel.org>
Signed-off-by: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>
---

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index 72d564c84499a..9fb8bb0afff74 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -357,6 +357,7 @@ static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func,
 	rcu_read_lock();
 	ideal_cpu = smp_processor_id() >> READ_ONCE(rtp->percpu_enqueue_shift);
 	chosen_cpu = cpumask_next(ideal_cpu - 1, cpu_possible_mask);
+	WARN_ON_ONCE(chosen_cpu >= rcu_task_cpu_ids);
 	rtpcp = per_cpu_ptr(rtp->rtpcpu, chosen_cpu);
 	if (!raw_spin_trylock_rcu_node(rtpcp)) { // irqs already disabled.
 		raw_spin_lock_rcu_node(rtpcp); // irqs already disabled.