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Message-ID: <20240312.Ohfumeel9aes@digikod.net>
Date: Tue, 12 Mar 2024 13:15:18 +0100
From: Mickaël Salaün <mic@...ikod.net>
To: David Gow <davidgow@...gle.com>
Cc: Brendan Higgins <brendanhiggins@...gle.com>,
Kees Cook <keescook@...omium.org>, Rae Moar <rmoar@...gle.com>,
Shuah Khan <skhan@...uxfoundation.org>, Alan Maguire <alan.maguire@...cle.com>,
Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
"H . Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
James Morris <jamorris@...ux.microsoft.com>, Luis Chamberlain <mcgrof@...nel.org>,
"Madhavan T . Venkataraman" <madvenka@...ux.microsoft.com>, Marco Pagani <marpagan@...hat.com>,
Paolo Bonzini <pbonzini@...hat.com>, Sean Christopherson <seanjc@...gle.com>,
Stephen Boyd <sboyd@...nel.org>, Thara Gopinath <tgopinath@...rosoft.com>,
Thomas Gleixner <tglx@...utronix.de>, Vitaly Kuznetsov <vkuznets@...hat.com>,
Wanpeng Li <wanpengli@...cent.com>, Zahra Tarkhani <ztarkhani@...rosoft.com>, kvm@...r.kernel.org,
linux-hardening@...r.kernel.org, linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-security-module@...r.kernel.org, linux-um@...ts.infradead.org, x86@...nel.org
Subject: Re: [PATCH v2 4/7] kunit: Handle test faults
On Tue, Mar 12, 2024 at 01:05:37PM +0800, David Gow wrote:
> On Sat, 2 Mar 2024 at 03:40, Mickaël Salaün <mic@...ikod.net> wrote:
> >
> > Previously, when a kernel test thread crashed (e.g. NULL pointer
> > dereference, general protection fault), the KUnit test hanged for 30
> > seconds and exited with a timeout error.
> >
> > Fix this issue by waiting on task_struct->vfork_done instead of the
> > custom kunit_try_catch.try_completion, and track the execution state by
> > initially setting try_result with -EFAULT and only setting it to 0 if
> > the test passed.
> >
> > Fix kunit_generic_run_threadfn_adapter() signature by returning 0
> > instead of calling kthread_complete_and_exit(). Because thread's exit
> > code is never checked, always set it to 0 to make it clear.
> >
> > Fix the -EINTR error message, which couldn't be reached until now.
> >
> > This is tested with a following patch.
> >
> > Cc: Brendan Higgins <brendanhiggins@...gle.com>
> > Cc: David Gow <davidgow@...gle.com>
> > Cc: Rae Moar <rmoar@...gle.com>
> > Cc: Shuah Khan <skhan@...uxfoundation.org>
> > Reviewed-by: Kees Cook <keescook@...omium.org>
> > Signed-off-by: Mickaël Salaün <mic@...ikod.net>
> > Link: https://lore.kernel.org/r/20240301194037.532117-5-mic@digikod.net
> > ---
>
> This works fine here, and looks good.
>
> The use of task_struct->vfork_done is a bit confusing, as there's no
> documentation (that I could find) about what vfork_done means for
> kthreads. From the code, it looks to just be a copy of
> kthread->exited, which is much more obvious a name.
Indeed
>
> Would it make sense to either (a) replace this with a call to
> to_kthread(), and kthread->exited, or (b) add a comment explaining
> what vfork_done means here. kthread_stop() itself is using
> to_kthread() and kthread->exited -- even though task_struct is also
> there -- so I'd feel a bit more comfortable with that option.
I used vfork_done because to_kthread() and struct kthread are private.
As for a vfork(2), vfork_done is useful to wait for the end of a task.
Feel free to add a comment explaining vfork_done. Thanks
>
> Otherwise,
> Reviewed-by: David Gow <davidgow@...gle.com>
>
> Cheers,
> -- David
>
> >
> > Changes since v1:
> > * Added Kees's Reviewed-by.
> > ---
> > include/kunit/try-catch.h | 3 ---
> > lib/kunit/try-catch.c | 14 +++++++-------
> > 2 files changed, 7 insertions(+), 10 deletions(-)
> >
> > diff --git a/include/kunit/try-catch.h b/include/kunit/try-catch.h
> > index c507dd43119d..7c966a1adbd3 100644
> > --- a/include/kunit/try-catch.h
> > +++ b/include/kunit/try-catch.h
> > @@ -14,13 +14,11 @@
> >
> > typedef void (*kunit_try_catch_func_t)(void *);
> >
> > -struct completion;
> > struct kunit;
> >
> > /**
> > * struct kunit_try_catch - provides a generic way to run code which might fail.
> > * @test: The test case that is currently being executed.
> > - * @try_completion: Completion that the control thread waits on while test runs.
> > * @try_result: Contains any errno obtained while running test case.
> > * @try: The function, the test case, to attempt to run.
> > * @catch: The function called if @try bails out.
> > @@ -46,7 +44,6 @@ struct kunit;
> > struct kunit_try_catch {
> > /* private: internal use only. */
> > struct kunit *test;
> > - struct completion *try_completion;
> > int try_result;
> > kunit_try_catch_func_t try;
> > kunit_try_catch_func_t catch;
> > diff --git a/lib/kunit/try-catch.c b/lib/kunit/try-catch.c
> > index cab8b24b5d5a..c6ee4db0b3bd 100644
> > --- a/lib/kunit/try-catch.c
> > +++ b/lib/kunit/try-catch.c
> > @@ -18,7 +18,7 @@
> > void __noreturn kunit_try_catch_throw(struct kunit_try_catch *try_catch)
> > {
> > try_catch->try_result = -EFAULT;
> > - kthread_complete_and_exit(try_catch->try_completion, -EFAULT);
> > + kthread_exit(0);
> > }
> > EXPORT_SYMBOL_GPL(kunit_try_catch_throw);
> >
> > @@ -26,9 +26,12 @@ static int kunit_generic_run_threadfn_adapter(void *data)
> > {
> > struct kunit_try_catch *try_catch = data;
> >
> > + try_catch->try_result = -EINTR;
> > try_catch->try(try_catch->context);
> > + if (try_catch->try_result == -EINTR)
> > + try_catch->try_result = 0;
> >
> > - kthread_complete_and_exit(try_catch->try_completion, 0);
> > + return 0;
> > }
> >
> > static unsigned long kunit_test_timeout(void)
> > @@ -58,13 +61,11 @@ static unsigned long kunit_test_timeout(void)
> >
> > void kunit_try_catch_run(struct kunit_try_catch *try_catch, void *context)
> > {
> > - DECLARE_COMPLETION_ONSTACK(try_completion);
> > struct kunit *test = try_catch->test;
> > struct task_struct *task_struct;
> > int exit_code, time_remaining;
> >
> > try_catch->context = context;
> > - try_catch->try_completion = &try_completion;
> > try_catch->try_result = 0;
> > task_struct = kthread_create(kunit_generic_run_threadfn_adapter,
> > try_catch, "kunit_try_catch_thread");
> > @@ -75,8 +76,7 @@ void kunit_try_catch_run(struct kunit_try_catch *try_catch, void *context)
> > }
> > get_task_struct(task_struct);
> > wake_up_process(task_struct);
> > -
> > - time_remaining = wait_for_completion_timeout(&try_completion,
> > + time_remaining = wait_for_completion_timeout(task_struct->vfork_done,
> > kunit_test_timeout());
> > if (time_remaining == 0) {
> > try_catch->try_result = -ETIMEDOUT;
> > @@ -92,7 +92,7 @@ void kunit_try_catch_run(struct kunit_try_catch *try_catch, void *context)
> > if (exit_code == -EFAULT)
> > try_catch->try_result = 0;
> > else if (exit_code == -EINTR)
> > - kunit_err(test, "wake_up_process() was never called\n");
> > + kunit_err(test, "try faulted\n");
> > else if (exit_code == -ETIMEDOUT)
> > kunit_err(test, "try timed out\n");
> > else if (exit_code)
> > --
> > 2.44.0
> >
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