From: "Paul E. McKenney" <paulmck@kernel.org>
To: rcu@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com,
rostedt@goodmis.org,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
"Paul E . McKenney" <paulmck@kernel.org>
Subject: [PATCH 08/19] srcu: Use IRQ_WORK_INIT_HARD for srcu's irq_work
Date: Fri, 18 Sep 2026 17:35:10 -0700 [thread overview]
Message-ID: <20260919003521.3134552-8-paulmck@kernel.org> (raw)
In-Reply-To: <13d6be93-8d9d-47a2-beb0-99c8a90938d4@paulmck-laptop>
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
The irq_work in srcu is used to schedule a delayed work. The work item
is not scheduled directly because it is not always possible wake a
thread directly.
On PREEMPT_RT the default irq_work is initialized with IRQ_WORK_LAZY and
is delayed to the irq_work thread. A system booted with the command line
"trace_event=…" will freeze during boot because the irq_work thread is
not yet deployed (and tracing uses synchronize_srcu() in
tp_rcu_cond_sync()).
The irq_work performs just a wakeup a thread, there is nothing wrong
with doing this from hardirq context on PREEMPT_RT.
Use IRQ_WORK_INIT_HARD for srcu's irq_work.
Fixes: 7c405fb3279b3 ("rcu: Use an intermediate irq_work to start process_srcu()")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
kernel/rcu/srcutree.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 61c2375ba2ec..6625420cfb43 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -259,7 +259,12 @@ static int init_srcu_struct_fields(struct srcu_struct *ssp, bool is_static, bool
mutex_init(&ssp->srcu_sup->srcu_barrier_mutex);
atomic_set(&ssp->srcu_sup->srcu_barrier_cpu_cnt, 0);
INIT_DELAYED_WORK(&ssp->srcu_sup->work, process_srcu);
- init_irq_work(&ssp->srcu_sup->irq_work, srcu_irq_work);
+ /*
+ * trace events started on the command line require SRCU before
+ * the irq_work kthread starts. Since all it does is a simple
+ * wakeup, having it as a hard irq, even on PREEMPT_RT is fine.
+ */
+ ssp->srcu_sup->irq_work = IRQ_WORK_INIT_HARD(srcu_irq_work);
ssp->srcu_sup->sda_is_static = is_static;
if (!is_static) {
ssp->sda = alloc_percpu(struct srcu_data);
--
2.40.1
next prev parent reply other threads:[~2026-09-19 0:35 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-19 0:35 [PATCH 0/19] Add atomic SRCU Paul E. McKenney
2026-09-19 0:35 ` [PATCH 01/19] srcutiny: Make a Tiny SRCU grace period imply an RCU grace period Paul E. McKenney
2026-09-19 0:35 ` [PATCH 02/19] srcutree: Suppress srcu_advance_state() mutex_lock in atomic Paul E. McKenney
2026-09-19 0:35 ` [PATCH 03/19] srcutree: Suppress to-big transition for atomic SRCU Paul E. McKenney
2026-09-19 0:35 ` [PATCH 04/19] srcutree: Add an atomic Tree SRCU Paul E. McKenney
2026-09-19 0:35 ` [PATCH 05/19] srcutiny: Add an atomic Tiny SRCU Paul E. McKenney
2026-09-19 0:35 ` [PATCH 06/19] rcutorture: Add support for testing synchronize_srcu_atomic() Paul E. McKenney
2026-09-19 0:35 ` [PATCH 07/19] srcutree: Disable preemption across synchronize_srcu_atomic() Paul E. McKenney
2026-09-19 0:35 ` Paul E. McKenney [this message]
2026-09-19 0:35 ` [PATCH 09/19] srcu: Fix WARN_ON() for rcu_segcblist_n_cbs() in cleanup_srcu_struct() Paul E. McKenney
2026-09-19 0:35 ` [PATCH 10/19] srcutree: Warn if Tiny SRCU readers are preempted Paul E. McKenney
2026-09-19 0:35 ` [PATCH 11/19] srcutree: Explicitly note DEFINE_SRCU() needs for srcu_barrier() Paul E. McKenney
2026-09-19 0:35 ` [PATCH 12/19] rcutorture: Add atomic-SRCU support to torture.sh Paul E. McKenney
2026-09-19 0:35 ` [PATCH 13/19] srcutree: Add reader-free fastpath to synchronize_srcu_atomic() Paul E. McKenney
2026-09-19 0:35 ` [PATCH 14/19] srcutree: Skip callback scheduling for atomic SRCU grace periods Paul E. McKenney
2026-09-19 0:35 ` [PATCH 15/19] srcutree: Remove srcu_barrier() sleep for atomic SRCU Paul E. McKenney
2026-09-19 0:35 ` [PATCH 16/19] srcu: Restrict atomic-SRCU non_block annotation to task context Paul E. McKenney
2026-09-19 0:35 ` [PATCH 17/19] srcutree: Make init_srcu_struct_atomic() prevent transition to big Paul E. McKenney
2026-09-19 0:35 ` [PATCH 18/19] srcutree: Don't transition atomic SRCU to big in srcu_gp_end() Paul E. McKenney
2026-09-19 0:35 ` [PATCH 19/19] srcutree: Skip torture to-big transition for atomic SRCU Paul E. McKenney
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