Re: [PATCH v5 13/17] rv: Add KUnit mock for current

[Wen Yang <wen.yang@linux.dev>]

On 7/30/26 13:13, Gabriele Monaco wrote:
> 
> 
> Il 29 luglio 2026 18:17:31 UTC, Wen Yang <wen.yang@linux.dev> ha scritto:
> 
>>> +#define rv_get_current() (unlikely(kunit_get_current_test()) ? rv_get_mock_current() : current)
>   
> ...
> 
>>> +/*
>>> + * rv_get_mock_current() is called only if we are running from a KUnit test.
>>> + * This can occur from a legitimate RV test or any unrelated test running when
>>> + * a real RV monitor is active and triggering events.
>>> + * We assume the former case is the only one where mock_current is not NULL and
>>> + * can occur only sequentially (KUnit doesn't run tests in parallel).
>>> + * We cannot rely on the test's context because there is no way to safely
>>> + * understand from which test we are running and KUnit utilities require
>>> + * locking, which is unsafe from NMI or scheduling context.
>>> + * Note that it is not possible for a real RV monitor to run when the RV KUnit
>>> + * tests are running (see rv_set_testing()).
>>> + */
>>> +static struct task_struct *mock_current;
>>> +
>>> +void rv_mock_current(struct task_struct *tsk)
>>> +{
>>> +	mock_current = tsk;
>>> +}
>>> +EXPORT_SYMBOL_IF_KUNIT(rv_mock_current);
>>> +
>>> +struct task_struct *rv_get_mock_current(void)
>>> +{
>>> +	return mock_current ?: current;
>>> +}
>>> +EXPORT_SYMBOL_GPL(rv_get_mock_current);
>>>    #endif
>>
>> rv_mock_current() uses EXPORT_SYMBOL_IF_KUNIT, but rv_get_mock_current() uses EXPORT_SYMBOL_GPL. Both are defined inside the same CONFIG_RV_MONITORS_KUNIT_TEST block, so rv_get_mock_current should use EXPORT_SYMBOL_IF_KUNIT as well, otherwise it leaks a test-only symbol into production builds.
>>
>> With that fixed:
>> Reviewed-by: Wen Yang <wen.yang@linux.dev>
> 
> Thanks for the review.
> This was intentional however: rv_get_current() can be called by any monitor, those don't have to be KUnit.
> Since rv_get_current() is a macro also calling rv_get_mock_current() we need to be able to link that too.
> 
> The idea is that a "real" (non-kunit) monitor handler could be run when interrupting a KUnit test (not an RV one, we make sure of that). In that case we do call rv_get_mock_current() and return current after the function call.
> 
> rv_mock_current() CANNOT be called outside of the RV KUnit test cases, it uses a global variable (for problems I tried to explain in the comment), so should be exported only to KUnit and called directly from the test case.
> 
> Does it make sense to you?
> 

Thanks for the explanation.
That does make sense.

One small thought though -- the kernel already provides 
KUNIT_STATIC_STUB_REDIRECT as the idiomatic way to handle this kind of 
pattern. It allows a production function to be transparently redirected 
to a stub during KUnit tests, with zero overhead when no test is running 
(since it uses the same static_branch_unlikely(&kunit_running) path as 
kunit_get_current_test()).

This might be a cleaner fit here, since it avoids exporting 
rv_mock_current() beyond KUnit and keeps the redirection logic internal 
to the test harness.

Just wanted to throw that out there -- what do you think?


diff --git a/kernel/trace/rv/rv_monitors_test.c 
b/kernel/trace/rv/rv_monitors_test.c
index 8026176eee90..f4e3e2e4a6d4 100644
--- a/kernel/trace/rv/rv_monitors_test.c
+++ b/kernel/trace/rv/rv_monitors_test.c
...
+struct task_struct *rv_current(void)
+{
+       KUNIT_STATIC_STUB_REDIRECT(rv_current);
+       return current;
+}
+EXPORT_SYMBOL_GPL(rv_current);

...

diff --git a/kernel/trace/rv/rv_monitors_test.c 
b/kernel/trace/rv/rv_monitors_test.c
index 8026176eee90..f4e3e2e4a6d4 100644
--- a/kernel/trace/rv/rv_monitors_test.c
+++ b/kernel/trace/rv/rv_monitors_test.c
...

+static struct task_struct *mock_current_task;
+
+static struct task_struct *rv_mock_current_fn(void)
+{
+       return mock_current_task ?: current;
+}
+
+void rv_mock_current(struct kunit *test, struct task_struct *tsk)
+{
+       mock_current_task = tsk;
+       if (tsk)
+               kunit_activate_static_stub(test, rv_current, 
rv_mock_current_fn);
+       else
+               kunit_deactivate_static_stub(test, rv_current);
+}
+EXPORT_SYMBOL_IF_KUNIT(rv_mock_current);


diff --git a/kernel/trace/rv/monitors/pagefault/pagefault_kunit.c 
b/kernel/trace/rv/monitors/pagefault/pagefault_kunit.c
index unchanged..unchanged 100644
--- a/kernel/trace/rv/monitors/pagefault/pagefault_kunit.c
+++ b/kernel/trace/rv/monitors/pagefault/pagefault_kunit.c
@@ -nn,7 +nn,7 @@ static void rv_test_pagefault(struct kunit *test)
         rv_pagefault_ops.handle_task_newtask(NULL, target, 0);
-       rv_mock_current(target);
+       rv_mock_current(test, target);



--
Best wishes,
Wen