linux-kernel - Re: [PATCH v2] uwb: properly check kthread

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Date:   Wed, 13 Sep 2017 18:53:37 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Johan Hovold <johan@...nel.org>,
        "Gustavo A . R . Silva" <garsilva@...eddedor.com>,
        Arvind Yadav <arvind.yadav.cs@...il.com>,
        USB list <linux-usb@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Kostya Serebryany <kcc@...gle.com>
Subject: Re: [PATCH v2] uwb: properly check kthread_run return value

On Wed, Sep 13, 2017 at 6:06 PM, Andrey Konovalov <andreyknvl@...gle.com> wrote:
> uwbd_start() calls kthread_run() and checks that the return value is
> not NULL. But the return value is not NULL in case kthread_run() fails,
> it takes the form of ERR_PTR(-EINTR).
>
> Use IS_ERR() instead.
>
> Also add a check to uwbd_stop().
>
> Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
> ---
>  drivers/uwb/uwbd.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/uwb/uwbd.c b/drivers/uwb/uwbd.c
> index 01c20a260a8b..2a3cc48d837c 100644
> --- a/drivers/uwb/uwbd.c
> +++ b/drivers/uwb/uwbd.c
> @@ -303,7 +303,7 @@ static int uwbd(void *param)
>  void uwbd_start(struct uwb_rc *rc)
>  {
>         rc->uwbd.task = kthread_run(uwbd, rc, "uwbd");
> -       if (rc->uwbd.task == NULL)
> +       if (IS_ERR(rc->uwbd.task))
>                 printk(KERN_ERR "UWB: Cannot start management daemon; "
>                        "UWB won't work\n");
>         else
> @@ -313,7 +313,8 @@ void uwbd_start(struct uwb_rc *rc)
>  /* Stop the UWB daemon and free any unprocessed events */
>  void uwbd_stop(struct uwb_rc *rc)
>  {
> -       kthread_stop(rc->uwbd.task);
> +       if (!IS_ERR(rc->uwbd.task))
> +               kthread_stop(rc->uwbd.task);

It looks weird to assign an error to rc->uwbd.task and leave it there.
I think it's better to not assign errors to rc->uwbd.task, i.e. it's
either a valid task or NULL.

>         uwbd_flush(rc);
>  }
>
> --
> 2.14.1.581.gf28d330327-goog
>