linux-kernel - Re: [PATCH v2 1/3] kernel: make kcov_common

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Date:   Wed, 14 Oct 2020 18:03:58 +0200
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Aleksandr Nogikh <a.nogikh@...il.com>
Cc:     "David S. Miller" <davem@...emloft.net>, kuba@...nel.org,
        Johannes Berg <johannes@...solutions.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Marco Elver <elver@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>, linux-wireless@...r.kernel.org,
        Aleksandr Nogikh <nogikh@...gle.com>
Subject: Re: [PATCH v2 1/3] kernel: make kcov_common_handle consider the
 current context

On Fri, Oct 9, 2020 at 7:02 PM Aleksandr Nogikh <a.nogikh@...il.com> wrote:
>
> From: Aleksandr Nogikh <nogikh@...gle.com>
>
> kcov_common_handle is a method that is used to obtain a "default" KCOV
> remote handle of the current process. The handle can later be passed
> to kcov_remote_start in order to collect coverage for the processing
> that is initiated by one process, but done in another. For details see
> Documentation/dev-tools/kcov.rst and comments in kernel/kcov.c.
>
> Presently, if kcov_common_handle is called in a hard IRQ context, it
> will return a handle for the interrupted process. This may lead to
> unreliable and incorrect coverage collection.

FWIW it's the same for soft IRQ context.

>
> Adjust the behavior of kcov_common_handle in the following way. If it
> is called in a task context, return the common handle for the
> currently running task. Otherwise, return 0. It will make the returned
> value more reliable and also will make it possible to use
> kcov_remote_handle in routines that can be called from any context.
>
> Signed-off-by: Aleksandr Nogikh <nogikh@...gle.com>
> ---
> v2:
> * Added this patch to the series.
> ---
>  kernel/kcov.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/kernel/kcov.c b/kernel/kcov.c
> index 6b8368be89c8..80bfe71bbe13 100644
> --- a/kernel/kcov.c
> +++ b/kernel/kcov.c
> @@ -1023,6 +1023,8 @@ EXPORT_SYMBOL(kcov_remote_stop);
>  /* See the comment before kcov_remote_start() for usage details. */
>  u64 kcov_common_handle(void)
>  {
> +       if (!in_task())
> +               return 0;
>         return current->kcov_handle;
>  }
>  EXPORT_SYMBOL(kcov_common_handle);
> --
> 2.28.0.1011.ga647a8990f-goog
>

Reviewed-by: Andrey Konovalov <andreyknvl@...gle.com>