[PATCH 6.18 022/198] srcu: Use irq_work to start GP in tiny SRCU

Greg Kroah-Hartman
2026-04-20T15:56:59Z

From: Joel Fernandes <joelagnelf@nvidia.com>

[ Upstream commit a6fc88b22bc8d12ad52e8412c667ec0f5bf055af ]

Tiny SRCU's srcu_gp_start_if_needed() directly calls schedule_work(),
which acquires the workqueue pool->lock.

This causes a lockdep splat when call_srcu() is called with a scheduler
lock held, due to:

call_srcu() [holding pi_lock]
srcu_gp_start_if_needed()
schedule_work() -> pool->lock

workqueue_init() / create_worker() [holding pool->lock]
wake_up_process() -> try_to_wake_up() -> pi_lock

Also add irq_work_sync() to cleanup_srcu_struct() to prevent a
use-after-free if a queued irq_work fires after cleanup begins.

Tested with rcutorture SRCU-T and no lockdep warnings.

[ Thanks to Boqun for similar fix in patch "rcu: Use an intermediate irq_work
to start process_srcu()" ]

Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Boqun Feng <boqun@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/linux/srcutiny.h | 4 ++++
kernel/rcu/srcutiny.c | 19 ++++++++++++++++++-
2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/include/linux/srcutiny.h b/include/linux/srcutiny.h
index 51ce25f07930e..1f9a226e6fd81 100644
--- a/include/linux/srcutiny.h
+++ b/include/linux/srcutiny.h
@@ -11,6 +11,7 @@
#ifndef _LINUX_SRCU_TINY_H
#define _LINUX_SRCU_TINY_H

+#include <linux/irq_work_types.h>
#include <linux/swait.h>

struct srcu_struct {
@@ -24,18 +25,21 @@ struct srcu_struct {
struct rcu_head *srcu_cb_head; /* Pending callbacks: Head. */
struct rcu_head **srcu_cb_tail; /* Pending callbacks: Tail. */
struct work_struct srcu_work; /* For driving grace periods. */
+ struct irq_work srcu_irq_work; /* Defer schedule_work() to irq work. */
#ifdef CONFIG_DEBUG_LOCK_ALLOC
struct lockdep_map dep_map;
#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
};

void srcu_drive_gp(struct work_struct *wp);
+void srcu_tiny_irq_work(struct irq_work *irq_work);

#define __SRCU_STRUCT_INIT(name, __ignored, ___ignored) \
{ \
.srcu_wq = __SWAIT_QUEUE_HEAD_INITIALIZER(name.srcu_wq), \
.srcu_cb_tail = &name.srcu_cb_head, \
.srcu_work = __WORK_INITIALIZER(name.srcu_work, srcu_drive_gp), \
+ .srcu_irq_work = { .func = srcu_tiny_irq_work }, \
__SRCU_DEP_MAP_INIT(name) \
}

diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
index e3b64a5e0ec7e..d9c11d5f0ea45 100644
--- a/kernel/rcu/srcutiny.c
+++ b/kernel/rcu/srcutiny.c
@@ -9,6 +9,7 @@
*/

#include <linux/export.h>
+#include <linux/irq_work.h>
#include <linux/mutex.h>
#include <linux/preempt.h>
#include <linux/rcupdate_wait.h>
@@ -41,6 +42,7 @@ static int init_srcu_struct_fields(struct srcu_struct *ssp)
ssp->srcu_idx_max = 0;
INIT_WORK(&ssp->srcu_work, srcu_drive_gp);
INIT_LIST_HEAD(&ssp->srcu_work.entry);
+ init_irq_work(&ssp->srcu_irq_work, srcu_tiny_irq_work);
return 0;
}

@@ -84,6 +86,7 @@ EXPORT_SYMBOL_GPL(init_srcu_struct);
void cleanup_srcu_struct(struct srcu_struct *ssp)
{
WARN_ON(ssp->srcu_lock_nesting[0] || ssp->srcu_lock_nesting[1]);
+ irq_work_sync(&ssp->srcu_irq_work);
flush_work(&ssp->srcu_work);
WARN_ON(ssp->srcu_gp_running);
WARN_ON(ssp->srcu_gp_waiting);
@@ -172,6 +175,20 @@ void srcu_drive_gp(struct work_struct *wp)
}
EXPORT_SYMBOL_GPL(srcu_drive_gp);

+/*
+ * Use an irq_work to defer schedule_work() to avoid acquiring the workqueue
+ * pool->lock while the caller might hold scheduler locks, causing lockdep
+ * splats due to workqueue_init() doing a wakeup.
+ */
+void srcu_tiny_irq_work(struct irq_work *irq_work)
+{
+ struct srcu_struct *ssp;
+
+ ssp = container_of(irq_work, struct srcu_struct, srcu_irq_work);
+ schedule_work(&ssp->srcu_work);
+}
+EXPORT_SYMBOL_GPL(srcu_tiny_irq_work);
+
static void srcu_gp_start_if_needed(struct srcu_struct *ssp)
{
unsigned long cookie;
@@ -184,7 +201,7 @@ static void srcu_gp_start_if_needed(struct srcu_struct *ssp)
WRITE_ONCE(ssp->srcu_idx_max, cookie);
if (!READ_ONCE(ssp->srcu_gp_running)) {
if (likely(srcu_init_done))
- schedule_work(&ssp->srcu_work);
+ irq_work_queue(&ssp->srcu_irq_work);
else if (list_empty(&ssp->srcu_work.entry))
list_add(&ssp->srcu_work.entry, &srcu_boot_list);
}
--
2.53.0