[Linux-kernel-mentees] [PATCH v2] lib: kunit: Provides a userspace memory context when tests are compiled as module

[Vitor Massaru Iha]

On Wed, Aug 19, 2020 at 6:05 PM Brendan Higgins
<brendanhiggins at google.com> wrote:
>
> On Fri, Jul 17, 2020 at 5:50 PM Vitor Massaru Iha <vitor at massaru.org> wrote:
> >
> > KUnit test cases run on kthreads, and kthreads don't have an
> > adddress space (current->mm is NULL), but processes have mm.
> >
> > The purpose of this patch is to allow to borrow mm to KUnit kthread
> > after userspace is brought up, because we know that there are processes
> > running, at least the process that loaded the module to borrow mm.
> >
> > This allows, for example, tests such as user_copy_kunit, which uses
> > vm_mmap, which needs current->mm.
> >
> > Signed-off-by: Vitor Massaru Iha <vitor at massaru.org>
>
> Can you put these together in the same patch series as you had before?
> When I asked you to split the patch up, I was just asking about that
> specific patch within the series. I still think all the patches go
> together.

Sure, I'll do that.

> As for this specific patch, I see one minor issue below; other than
> that, this looks good to me, so:
>
> Reviewed-by: Brendan Higgins <brendanhiggins at google.com>
>
> > ---
> > v2:
> >     * splitted patch in 3:
> >         - Allows to install and load modules in root filesystem;
> >         - Provides an userspace memory context when tests are compiled
> >           as module;
> >         - Convert test_user_copy to KUnit test;
> >     * added documentation;
> >     * added more explanation;
> >     * tested a pointer;
> >     * released mput();
> > ---
> >  Documentation/dev-tools/kunit/usage.rst | 14 ++++++++++++++
> >  include/kunit/test.h                    | 12 ++++++++++++
> >  lib/kunit/try-catch.c                   | 15 ++++++++++++++-
> >  3 files changed, 40 insertions(+), 1 deletion(-)
> >
> > diff --git a/Documentation/dev-tools/kunit/usage.rst b/Documentation/dev-tools/kunit/usage.rst
> > index 3c3fe8b5fecc..9f909157be34 100644
> > --- a/Documentation/dev-tools/kunit/usage.rst
> > +++ b/Documentation/dev-tools/kunit/usage.rst
> > @@ -448,6 +448,20 @@ We can now use it to test ``struct eeprom_buffer``:
> >
> >  .. _kunit-on-non-uml:
> >
> > +User-space context
> > +------------------
> > +
> > +I case you need a user-space context, for now this is only possible through
> > +tests compiled as a module. And it will be necessary to use a root filesystem
> > +and uml_utilities.
> > +
> > +Example:
> > +
> > +.. code-block:: bash
> > +
> > +   ./tools/testing/kunit/kunit.py run --timeout=60 --uml_rootfs_dir=.uml_rootfs
> > +
> > +
> >  KUnit on non-UML architectures
> >  ==============================
>
> I think the above documentation change belongs in the other related
> patch where you introduce the --uml_rootfs_dir flag.
>
> > diff --git a/include/kunit/test.h b/include/kunit/test.h
> > index 59f3144f009a..ae3337139c65 100644
> > --- a/include/kunit/test.h
> > +++ b/include/kunit/test.h
> > @@ -222,6 +222,18 @@ struct kunit {
> >          * protect it with some type of lock.
> >          */
> >         struct list_head resources; /* Protected by lock. */
> > +       /*
> > +        * KUnit test cases run on kthreads, and kthreads don't have an
> > +        * adddress space (current->mm is NULL), but processes have mm.
> > +        *
> > +        * The purpose of this mm_struct is to allow to borrow mm to KUnit kthread
> > +        * after userspace is brought up, because we know that there are processes
> > +        * running, at least the process that loaded the module to borrow mm.
> > +        *
> > +        * This allows, for example, tests such as user_copy_kunit, which uses
> > +        * vm_mmap, which needs current->mm.
> > +        */
> > +       struct mm_struct *mm;
> >  };
> >
> >  void kunit_init_test(struct kunit *test, const char *name, char *log);
> > diff --git a/lib/kunit/try-catch.c b/lib/kunit/try-catch.c
> > index 0dd434e40487..d03e2093985b 100644
> > --- a/lib/kunit/try-catch.c
> > +++ b/lib/kunit/try-catch.c
> > @@ -11,7 +11,8 @@
> >  #include <linux/completion.h>
> >  #include <linux/kernel.h>
> >  #include <linux/kthread.h>
> > -
> > +#include <linux/sched/mm.h>
> > +#include <linux/sched/task.h>
> >  #include "try-catch-impl.h"
> >
> >  void __noreturn kunit_try_catch_throw(struct kunit_try_catch *try_catch)
> > @@ -24,8 +25,17 @@ EXPORT_SYMBOL_GPL(kunit_try_catch_throw);
> >  static int kunit_generic_run_threadfn_adapter(void *data)
> >  {
> >         struct kunit_try_catch *try_catch = data;
> > +       struct kunit *test = try_catch->test;
> > +
> > +       if (test != NULL && test->mm != NULL)
> > +               kthread_use_mm(test->mm);
> >
> >         try_catch->try(try_catch->context);
> > +       if (test != NULL && test->mm != NULL) {
> > +               kthread_unuse_mm(test->mm);
> > +               mmput(test->mm);
> > +               test->mm = NULL;
> > +       }
> >
> >         complete_and_exit(try_catch->try_completion, 0);
> >  }
> > @@ -65,6 +75,9 @@ void kunit_try_catch_run(struct kunit_try_catch *try_catch, void *context)
> >         try_catch->context = context;
> >         try_catch->try_completion = &try_completion;
> >         try_catch->try_result = 0;
> > +
> > +       test->mm = get_task_mm(current);
> > +
> >         task_struct = kthread_run(kunit_generic_run_threadfn_adapter,
> >                                   try_catch,
> >                                   "kunit_try_catch_thread");
> >
> > base-commit: 725aca9585956676687c4cb803e88f770b0df2b2
> > prerequisite-patch-id: 5e5f9a8a05c5680fda1b04c9ab1b95ce91dc88b2
> > prerequisite-patch-id: 4d997940f4a9f303424af9bac412de1af861f9d9
> > prerequisite-patch-id: 582b6d9d28ce4b71628890ec832df6522ca68de0
> > --
> > 2.26.2
> >