-From a5f2a6e457ca8fe205976269d9d835b398a03f94 Mon Sep 17 00:00:00 2001
-From: Sasha Levin <sashal@kernel.org>
-Date: Mon, 23 Mar 2026 20:14:18 -0400
-Subject: srcu: Use irq_work to start GP in tiny SRCU
-
-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 4d96bbdb45f08..6f39d3d8ef879 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 4dcbf8aa80ff7..ddea40b68e5f6 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>
-@@ -37,6 +38,7 @@ 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;
- }
-
-@@ -80,6 +82,7 @@ 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);
-@@ -168,6 +171,20 @@ 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;
-@@ -181,7 +198,7 @@ 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
-
projects / thirdparty / kernel / stable-queue.git / commitdiff
