From 893cdaaa3977be6afb3a7f756fbfd7be83f68d8c Mon Sep 17 00:00:00 2001 From: Wander Lairson Costa Date: Wed, 14 Jun 2023 09:23:22 -0300 Subject: [PATCH] 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. Suggested-by: Oleg Nesterov Suggested-by: Sebastian Andrzej Siewior Suggested-by: Peter Zijlstra Signed-off-by: Wander Lairson Costa Signed-off-by: Peter Zijlstra (Intel) Link: https://lore.kernel.org/r/20230614122323.37957-3-wander@redhat.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 6b687c155fb6..a23af225c898 100644 --- a/include/linux/sched/task.h +++ b/include/linux/sched/task.h @@ -125,6 +125,19 @@ 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 @@ -145,10 +158,7 @@ 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); } DEFINE_FREE(put_task, struct task_struct *, if (_T) put_task_struct(_T)) -- 2.25.1