Re: [PATCH v4 13/17] rv: Add KUnit stub for current

[Gabriele Monaco <gmonaco@redhat.com>]

On Fri, 2026-07-17 at 17:46 +0200, Gabriele Monaco wrote:
> Some monitors do not only rely on tracepoint arguments but also on the
> currently executing task.
> This makes it more challenging to mock events in KUnit.
> 
> Define wrapper functions around current, the functionality is stubbed
> only during KUnit, however the additional function call is necessary
> whenever the KUnit tests are built in.
> 
> Reviewed-by: Nam Cao <namcao@linutronix.de>
> Signed-off-by: Gabriele Monaco <gmonaco@redhat.com>

As reported by sashiko, using KUnit's standard stubbing can be dangerous. In the
rare case of an NMI causing an RV event (e.g. a pagefault) when an unrelated
KUnit test is running, the stub would end up using locks and causing issues.

Additionally, it isn't ideal to downgrade to a function call directly if the
tests are built, which is for instance the default on the stock Fedora kernel
(CONFIG_KUNIT_ALL_TESTS=m).

I'm soon going to send a V5 addressing both: no stub and function call only if
KUnit is really running.
I'll reset the review since the patch essentially changes.

> ---
>  include/rv/da_monitor.h                       |  1 +
>  include/rv/kunit.h                            | 13 +++++++++-
>  include/rv/ltl_monitor.h                      |  1 +
>  kernel/trace/rv/Kconfig                       |  3 +++
>  .../trace/rv/monitors/pagefault/pagefault.c   |  2 +-
>  kernel/trace/rv/monitors/sleep/sleep.c        | 24 +++++++++----------
>  kernel/trace/rv/rv.c                          |  8 +++++++
>  kernel/trace/rv/rv_monitors_test.c            |  9 +++++++
>  8 files changed, 47 insertions(+), 14 deletions(-)
> 
> diff --git a/include/rv/da_monitor.h b/include/rv/da_monitor.h
> index 773564720ba1..9f7ba443d777 100644
> --- a/include/rv/da_monitor.h
> +++ b/include/rv/da_monitor.h
> @@ -16,6 +16,7 @@
>  
>  #include <rv/automata.h>
>  #include <linux/rv.h>
> +#include <rv/kunit.h>
>  #include <linux/stringify.h>
>  #include <linux/bug.h>
>  #include <linux/sched.h>
> diff --git a/include/rv/kunit.h b/include/rv/kunit.h
> index ff98b5137285..6d16a422a80c 100644
> --- a/include/rv/kunit.h
> +++ b/include/rv/kunit.h
> @@ -2,7 +2,10 @@
>  /*
>   * Copyright (C) 2026-2029 Red Hat, Inc. Gabriele Monaco <gmonaco@redhat.com>
>   *
> - * Declaration of utilities to run KUnit tests.
> + * Declaration of wrappers to allow stubbing core functionality, like
> current,
> + * and other testing utilities.
> + * Necessary only when mocking may be needed. If the RV KUnit test is
> + * enabled, the wrappers incur an additional function call overhead.
>   */
>  
>  #ifndef _RV_KUNIT_H
> @@ -16,6 +19,7 @@
>  
>  int rv_set_testing(struct kunit_suite *suite);
>  void rv_clear_testing(struct kunit_suite *suite);
> +struct task_struct *rv_get_current(void);
>  
>  #define RV_KUNIT_MAX_MOCK_TASKS 8
>  
> @@ -23,6 +27,7 @@ struct rv_kunit_ctx {
>  	int reactions, expected;
>  	int mock_task_count;
>  	struct task_struct *mock_tasks[RV_KUNIT_MAX_MOCK_TASKS];
> +	struct task_struct *curr;
>  };
>  
>  #define RV_KUNIT_EXPECT_REACTION(test, ctx)                             \
> @@ -57,5 +62,11 @@ void prepare_test(struct kunit *test, const struct
> rv_kunit_mon *mon);
>  void teardown_test(void *arg);
>  struct task_struct *rv_kunit_alloc_mock_task(struct kunit *test);
>  
> +#define rv_mock_current(ctx, task) (ctx->curr = task)
> +
> +#else /* !CONFIG_RV_MONITORS_KUNIT_TEST */
> +
> +#define rv_get_current() current
> +
>  #endif /* CONFIG_RV_MONITORS_KUNIT_TEST */
>  #endif /* _RV_KUNIT_H */
> diff --git a/include/rv/ltl_monitor.h b/include/rv/ltl_monitor.h
> index 56e83edcf0c4..d7dc01db4dd9 100644
> --- a/include/rv/ltl_monitor.h
> +++ b/include/rv/ltl_monitor.h
> @@ -9,6 +9,7 @@
>  #include <linux/stringify.h>
>  #include <linux/seq_buf.h>
>  #include <rv/instrumentation.h>
> +#include <rv/kunit.h>
>  #include <trace/events/task.h>
>  #include <trace/events/sched.h>
>  
> diff --git a/kernel/trace/rv/Kconfig b/kernel/trace/rv/Kconfig
> index 34c1feb35a9b..7bae9723cdbf 100644
> --- a/kernel/trace/rv/Kconfig
> +++ b/kernel/trace/rv/Kconfig
> @@ -121,4 +121,7 @@ config RV_MONITORS_KUNIT_TEST
>  	  These tests verify that monitors correctly detect violations by
>  	  triggering fake events and validating the expected reactions.
>  
> +	  Enabling this may slightly increase overhead of some monitors even
> +	  when the KUnit test is not running.
> +
>  	  If unsure, say N.
> diff --git a/kernel/trace/rv/monitors/pagefault/pagefault.c
> b/kernel/trace/rv/monitors/pagefault/pagefault.c
> index 5e1a2a606783..e52500fd2de0 100644
> --- a/kernel/trace/rv/monitors/pagefault/pagefault.c
> +++ b/kernel/trace/rv/monitors/pagefault/pagefault.c
> @@ -38,7 +38,7 @@ static void ltl_atoms_init(struct task_struct *task, struct
> ltl_monitor *mon, bo
>  static void handle_page_fault(void *data, unsigned long address, struct
> pt_regs *regs,
>  			      unsigned long error_code)
>  {
> -	ltl_atom_pulse(current, LTL_PAGEFAULT, true);
> +	ltl_atom_pulse(rv_get_current(), LTL_PAGEFAULT, true);
>  }
>  
>  static int enable_pagefault(void)
> diff --git a/kernel/trace/rv/monitors/sleep/sleep.c
> b/kernel/trace/rv/monitors/sleep/sleep.c
> index 12328ce663f5..71d2005ce520 100644
> --- a/kernel/trace/rv/monitors/sleep/sleep.c
> +++ b/kernel/trace/rv/monitors/sleep/sleep.c
> @@ -102,7 +102,7 @@ static void handle_sched_waking(void *data, struct
> task_struct *task)
>  	if (this_cpu_read(hardirq_context)) {
>  		ltl_atom_pulse(task, LTL_WOKEN_BY_HARDIRQ, true);
>  	} else if (in_task()) {
> -		if (current->prio <= task->prio)
> +		if (rv_get_current()->prio <= task->prio)
>  			ltl_atom_pulse(task,
> LTL_WOKEN_BY_EQUAL_OR_HIGHER_PRIO, true);
>  	} else if (in_nmi()) {
>  		ltl_atom_pulse(task, LTL_WOKEN_BY_NMI, true);
> @@ -112,12 +112,12 @@ static void handle_sched_waking(void *data, struct
> task_struct *task)
>  static void handle_contention_begin(void *data, void *lock, unsigned int
> flags)
>  {
>  	if (flags & LCB_F_RT)
> -		ltl_atom_update(current, LTL_BLOCK_ON_RT_MUTEX, true);
> +		ltl_atom_update(rv_get_current(), LTL_BLOCK_ON_RT_MUTEX,
> true);
>  }
>  
>  static void handle_contention_end(void *data, void *lock, int ret)
>  {
> -	ltl_atom_update(current, LTL_BLOCK_ON_RT_MUTEX, false);
> +	ltl_atom_update(rv_get_current(), LTL_BLOCK_ON_RT_MUTEX, false);
>  }
>  
>  static void handle_sys_enter(void *data, struct pt_regs *regs, long id)
> @@ -126,7 +126,7 @@ static void handle_sys_enter(void *data, struct pt_regs
> *regs, long id)
>  	unsigned long args[6];
>  	int op, cmd;
>  
> -	mon = ltl_get_monitor(current);
> +	mon = ltl_get_monitor(rv_get_current());
>  
>  	switch (id) {
>  #ifdef __NR_clock_nanosleep
> @@ -135,11 +135,11 @@ static void handle_sys_enter(void *data, struct pt_regs
> *regs, long id)
>  #ifdef __NR_clock_nanosleep_time64
>  	case __NR_clock_nanosleep_time64:
>  #endif
> -		syscall_get_arguments(current, regs, args);
> +		syscall_get_arguments(rv_get_current(), regs, args);
>  		ltl_atom_set(mon, LTL_NANOSLEEP_CLOCK_MONOTONIC, args[0] ==
> CLOCK_MONOTONIC);
>  		ltl_atom_set(mon, LTL_NANOSLEEP_CLOCK_TAI, args[0] ==
> CLOCK_TAI);
>  		ltl_atom_set(mon, LTL_NANOSLEEP_TIMER_ABSTIME, args[1] ==
> TIMER_ABSTIME);
> -		ltl_atom_update(current, LTL_CLOCK_NANOSLEEP, true);
> +		ltl_atom_update(rv_get_current(), LTL_CLOCK_NANOSLEEP, true);
>  		break;
>  
>  #ifdef __NR_futex
> @@ -148,25 +148,25 @@ static void handle_sys_enter(void *data, struct pt_regs
> *regs, long id)
>  #ifdef __NR_futex_time64
>  	case __NR_futex_time64:
>  #endif
> -		syscall_get_arguments(current, regs, args);
> +		syscall_get_arguments(rv_get_current(), regs, args);
>  		op = args[1];
>  		cmd = op & FUTEX_CMD_MASK;
>  
>  		switch (cmd) {
>  		case FUTEX_LOCK_PI:
>  		case FUTEX_LOCK_PI2:
> -			ltl_atom_update(current, LTL_FUTEX_LOCK_PI, true);
> +			ltl_atom_update(rv_get_current(), LTL_FUTEX_LOCK_PI,
> true);
>  			break;
>  		case FUTEX_WAIT:
>  		case FUTEX_WAIT_BITSET:
>  		case FUTEX_WAIT_REQUEUE_PI:
> -			ltl_atom_update(current, LTL_FUTEX_WAIT, true);
> +			ltl_atom_update(rv_get_current(), LTL_FUTEX_WAIT,
> true);
>  			break;
>  		}
>  		break;
>  #ifdef __NR_epoll_wait
>  	case __NR_epoll_wait:
> -		ltl_atom_update(current, LTL_EPOLL_WAIT, true);
> +		ltl_atom_update(rv_get_current(), LTL_EPOLL_WAIT, true);
>  		break;
>  #endif
>  	}
> @@ -174,7 +174,7 @@ static void handle_sys_enter(void *data, struct pt_regs
> *regs, long id)
>  
>  static void handle_sys_exit(void *data, struct pt_regs *regs, long ret)
>  {
> -	struct ltl_monitor *mon = ltl_get_monitor(current);
> +	struct ltl_monitor *mon = ltl_get_monitor(rv_get_current());
>  
>  	ltl_atom_set(mon, LTL_FUTEX_LOCK_PI, false);
>  	ltl_atom_set(mon, LTL_FUTEX_WAIT, false);
> @@ -182,7 +182,7 @@ static void handle_sys_exit(void *data, struct pt_regs
> *regs, long ret)
>  	ltl_atom_set(mon, LTL_NANOSLEEP_CLOCK_TAI, false);
>  	ltl_atom_set(mon, LTL_NANOSLEEP_TIMER_ABSTIME, false);
>  	ltl_atom_set(mon, LTL_EPOLL_WAIT, false);
> -	ltl_atom_update(current, LTL_CLOCK_NANOSLEEP, false);
> +	ltl_atom_update(rv_get_current(), LTL_CLOCK_NANOSLEEP, false);
>  }
>  
>  static void handle_kthread_stop(void *data, struct task_struct *task)
> diff --git a/kernel/trace/rv/rv.c b/kernel/trace/rv/rv.c
> index cfe950fef3b4..edb10812f296 100644
> --- a/kernel/trace/rv/rv.c
> +++ b/kernel/trace/rv/rv.c
> @@ -142,6 +142,7 @@
>  #include <linux/module.h>
>  #include <linux/init.h>
>  #include <linux/slab.h>
> +#include <kunit/static_stub.h>
>  
>  #ifdef CONFIG_RV_MON_EVENTS
>  #define CREATE_TRACE_POINTS
> @@ -893,4 +894,11 @@ void rv_clear_testing(struct kunit_suite *suite)
>  	mutex_unlock(&rv_interface_lock);
>  }
>  EXPORT_SYMBOL_IF_KUNIT(rv_clear_testing);
> +
> +struct task_struct *rv_get_current(void)
> +{
> +	KUNIT_STATIC_STUB_REDIRECT(rv_get_current);
> +	return current;
> +}
> +EXPORT_SYMBOL_GPL(rv_get_current);
>  #endif
> diff --git a/kernel/trace/rv/rv_monitors_test.c
> b/kernel/trace/rv/rv_monitors_test.c
> index 2145c85d4c9a..2108973383b2 100644
> --- a/kernel/trace/rv/rv_monitors_test.c
> +++ b/kernel/trace/rv/rv_monitors_test.c
> @@ -106,6 +106,13 @@ struct task_struct *rv_kunit_alloc_mock_task(struct kunit
> *test)
>  	return tsk;
>  }
>  
> +static struct task_struct *stub_rv_get_current(void)
> +{
> +	if (active_ctx && active_ctx->curr)
> +		return active_ctx->curr;
> +	return current;
> +}
> +
>  static int rv_mon_test_init(struct kunit *test)
>  {
>  	struct rv_kunit_ctx *ctx;
> @@ -115,6 +122,8 @@ static int rv_mon_test_init(struct kunit *test)
>  
>  	test->priv = ctx;
>  
> +	kunit_activate_static_stub(test, rv_get_current,
> stub_rv_get_current);
> +
>  	return 0;
>  }
>