[PATCH v5 12/13] rcu-tasks-trace: Assert no reader is held on return to userspace

[bot+bpf-ci at kernel.org]

> diff --git a/include/linux/irq-entry-common.h b/include/linux/irq-entry-common.h
> index e19b41ee6b18..d42568a488a7 100644
> --- a/include/linux/irq-entry-common.h
> +++ b/include/linux/irq-entry-common.h
> @@ -5,6 +5,7 @@
>  #include <linux/context_tracking.h>
>  #include <linux/hrtimer_rearm.h>
>  #include <linux/kmsan.h>
> +#include <linux/rcupdate_trace.h>
>  #include <linux/rseq_entry.h>
>  #include <linux/static_call_types.h>
>  #include <linux/syscalls.h>
> @@ -214,6 +215,7 @@ static __always_inline void __exit_to_user_mode_validate(void)
>  {
>  	/* Ensure that kernel state is sane for a return to userspace */
>  	kmap_assert_nomap();
> +	rcu_tasks_trace_assert_idle();
>  	lockdep_assert_irqs_disabled();
>  	lockdep_sys_exit();
>  }
> diff --git a/include/linux/rcupdate_trace.h b/include/linux/rcupdate_trace.h
> index dcdb11643496..9eb7f92c710b 100644
> --- a/include/linux/rcupdate_trace.h
> +++ b/include/linux/rcupdate_trace.h
> @@ -217,6 +217,12 @@ unsigned long rcu_tasks_trace_batches_completed(void);
>  // Placeholders to enable stepwise transition.
>  void __init rcu_tasks_trace_suppress_unused(void);
>
> +/* A task must never reach userspace inside an rcu_read_lock_trace() reader. */
> +static inline void rcu_tasks_trace_assert_idle(void)
> +{
> +	WARN_ON_ONCE(IS_ENABLED(CONFIG_PROVE_RCU) && READ_ONCE(current->trc_reader_nesting));
> +}
> +
          ^^^^

This isn't a bug, but since rcu_read_lock_trace_held() already exists a
few lines up, would rcu_tasks_trace_assert_no_reader() (or
..._assert_not_held()) read better here than ..._assert_idle(), given
that "idle" already means the dynticks/RCU-not-watching state elsewhere
in RCU?

And would it be worth moving it above the "Placeholders to enable
stepwise transition" comment so it does not read as part of that group?

>  #else
>  static inline unsigned long rcu_tasks_trace_batches_completed(void) { return 0; }
>  /*

[ ... ]


---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

CI run summary: https://github.com/kernel-patches/bpf/actions/runs/35680506278