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References: <20200715031120.1002016-1-vitor@massaru.org> <20200715031120.1002016-3-vitor@massaru.org>
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From:   Brendan Higgins <brendanhiggins@google.com>
Date:   Wed, 15 Jul 2020 17:37:06 -0700
Message-ID: <CAFd5g47HPGjX4AYuBCjH8DqSUMNO+yqjudWH+ZNovStM+aXExA@mail.gmail.com>
Subject: Re: [RFC 2/3] lib: Allows to borrow mm in userspace on KUnit
To:     Vitor Massaru Iha <vitor@massaru.org>
Cc:     KUnit Development <kunit-dev@googlegroups.com>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Kees Cook <keescook@chromium.org>,
        David Gow <davidgow@google.com>,
        Shuah Khan <skhan@linuxfoundation.org>,
        linux-kernel-mentees@lists.linuxfoundation.org
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On Tue, Jul 14, 2020 at 8:11 PM Vitor Massaru Iha <vitor@massaru.org> wrote:

Probably want to add more of a description here as what you are doing
is not entirely trivial to someone not familiar with mm contexts.

>
> Signed-off-by: Vitor Massaru Iha <vitor@massaru.org>
> ---
>  include/kunit/test.h  |  1 +
>  lib/kunit/try-catch.c | 15 ++++++++++++++-
>  2 files changed, 15 insertions(+), 1 deletion(-)
>
> diff --git a/include/kunit/test.h b/include/kunit/test.h
> index 59f3144f009a..49c38bdcb93e 100644
> --- a/include/kunit/test.h
> +++ b/include/kunit/test.h
> @@ -222,6 +222,7 @@ struct kunit {
>          * protect it with some type of lock.
>          */
>         struct list_head resources; /* Protected by lock. */
> +       struct mm_struct *mm;

Part of me thinks we should put a better name here, part of me thinks
it is fine because it matches the convention.

Either way, this DEFINITELY deserves a comment explaining what it is,
why it exists, and how it should/shouldn't be used.

>  };
>
>  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..f677c2f2a51a 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->mm != NULL)
> +               kthread_use_mm(try_catch->test->mm);
>
>         try_catch->try(try_catch->context);
> +       if (try_catch->test->mm) {

Here and below: You already have a pointer to test. You should use it.

> +               if (test->mm != NULL)
> +                       kthread_unuse_mm(try_catch->test->mm);
> +               try_catch->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");
> --
> 2.26.2
>