From 45088f69b7318ddc1c438d0595f09ded3109b475 Mon Sep 17 00:00:00 2001
From: Wander Lairson Costa <wander@redhat.com>
Date: Wed, 14 Jun 2023 09:23:22 -0300
Subject: [PATCH 57/62] sched: avoid false lockdep splat in put_task_struct()
In put_task_struct(), a spin_lock is indirectly acquired under the kernel
stock. When running the kernel in real-time (RT) configuration, the
operation is dispatched to a preemptible context call to ensure
guaranteed preemption. However, if PROVE_RAW_LOCK_NESTING is enabled
and __put_task_struct() is called while holding a raw_spinlock, lockdep
incorrectly reports an "Invalid lock context" in the stock kernel.
This false splat occurs because lockdep is unaware of the different
route taken under RT. To address this issue, override the inner wait
type to prevent the false lockdep splat.
Signed-off-by: Wander Lairson Costa <wander@redhat.com>
Suggested-by: Oleg Nesterov <oleg@redhat.com>
Suggested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Luis Goncalves <lgoncalv@redhat.com>
Link: https://lore.kernel.org/r/20230614122323.37957-3-wander@redhat.com
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
(cherry picked from commit a5e446e728e89d5f5c5e427cc919bc7813c64c28)
Signed-off-by: Clark Williams <clark.williams@gmail.com>
---
include/linux/sched/task.h | 18 ++++++++++++++----
1 file changed, 14 insertions(+), 4 deletions(-)
diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h
index 7291fb6399d2..08ddeb0dcfc7 100644
--- a/include/linux/sched/task.h
+++ b/include/linux/sched/task.h
@@ -119,6 +119,19 @@ static inline void put_task_struct(struct task_struct *t)
if (!refcount_dec_and_test(&t->usage))
return;
+ /*
+ * In !RT, it is always safe to call __put_task_struct().
+ * Under RT, we can only call it in preemptible context.
+ */
+ if (!IS_ENABLED(CONFIG_PREEMPT_RT) || preemptible()) {
+ static DEFINE_WAIT_OVERRIDE_MAP(put_task_map, LD_WAIT_SLEEP);
+
+ lock_map_acquire_try(&put_task_map);
+ __put_task_struct(t);
+ lock_map_release(&put_task_map);
+ return;
+ }
+
/*
* under PREEMPT_RT, we can't call put_task_struct
* in atomic context because it will indirectly
@@ -139,10 +152,7 @@ static inline void put_task_struct(struct task_struct *t)
* when it fails to fork a process. Therefore, there is no
* way it can conflict with put_task_struct().
*/
- if (IS_ENABLED(CONFIG_PREEMPT_RT) && !preemptible())
- call_rcu(&t->rcu, __put_task_struct_rcu_cb);
- else
- __put_task_struct(t);
+ call_rcu(&t->rcu, __put_task_struct_rcu_cb);
}
static inline void put_task_struct_many(struct task_struct *t, int nr)
--
2.41.0