linux-kernel - Re: [PATCH v4 3/7] kcov: move t->kcov assignments into kcov

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Date:   Thu, 4 Jun 2020 14:09:20 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Andrew Morton <akpm@...ux-foundation.org>,
        USB list <linux-usb@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Alexander Potapenko <glider@...gle.com>,
        Marco Elver <elver@...gle.com>
Subject: Re: [PATCH v4 3/7] kcov: move t->kcov assignments into kcov_start/stop

On Thu, Mar 26, 2020 at 3:44 PM Andrey Konovalov <andreyknvl@...gle.com> wrote:
>
> Every time kcov_start/stop() is called, t->kcov is also assigned, so
> move the assignment into the functions.
>
> Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>

Reviewed-by: Dmitry Vyukov <dvyukov@...gle.com>

> ---
>  kernel/kcov.c | 16 +++++++---------
>  1 file changed, 7 insertions(+), 9 deletions(-)
>
> diff --git a/kernel/kcov.c b/kernel/kcov.c
> index cc5900ac2467..888d0a236b04 100644
> --- a/kernel/kcov.c
> +++ b/kernel/kcov.c
> @@ -309,10 +309,12 @@ void notrace __sanitizer_cov_trace_switch(u64 val, u64 *cases)
>  EXPORT_SYMBOL(__sanitizer_cov_trace_switch);
>  #endif /* ifdef CONFIG_KCOV_ENABLE_COMPARISONS */
>
> -static void kcov_start(struct task_struct *t, unsigned int size,
> -                       void *area, enum kcov_mode mode, int sequence)
> +static void kcov_start(struct task_struct *t, struct kcov *kcov,
> +                       unsigned int size, void *area, enum kcov_mode mode,
> +                       int sequence)
>  {
>         kcov_debug("t = %px, size = %u, area = %px\n", t, size, area);
> +       t->kcov = kcov;
>         /* Cache in task struct for performance. */
>         t->kcov_size = size;
>         t->kcov_area = area;
> @@ -326,6 +328,7 @@ static void kcov_stop(struct task_struct *t)
>  {
>         WRITE_ONCE(t->kcov_mode, KCOV_MODE_DISABLED);
>         barrier();
> +       t->kcov = NULL;
>         t->kcov_size = 0;
>         t->kcov_area = NULL;
>  }
> @@ -333,7 +336,6 @@ static void kcov_stop(struct task_struct *t)
>  static void kcov_task_reset(struct task_struct *t)
>  {
>         kcov_stop(t);
> -       t->kcov = NULL;
>         t->kcov_sequence = 0;
>         t->kcov_handle = 0;
>  }
> @@ -584,9 +586,8 @@ static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd,
>                         return mode;
>                 kcov_fault_in_area(kcov);
>                 kcov->mode = mode;
> -               kcov_start(t, kcov->size, kcov->area, kcov->mode,
> +               kcov_start(t, kcov, kcov->size, kcov->area, kcov->mode,
>                                 kcov->sequence);
> -               t->kcov = kcov;
>                 kcov->t = t;
>                 /* Put either in kcov_task_exit() or in KCOV_DISABLE. */
>                 kcov_get(kcov);
> @@ -778,7 +779,6 @@ void kcov_remote_start(u64 handle)
>         kcov = remote->kcov;
>         /* Put in kcov_remote_stop(). */
>         kcov_get(kcov);
> -       t->kcov = kcov;
>         /*
>          * Read kcov fields before unlock to prevent races with
>          * KCOV_DISABLE / kcov_remote_reset().
> @@ -792,7 +792,6 @@ void kcov_remote_start(u64 handle)
>         if (!area) {
>                 area = vmalloc(size * sizeof(unsigned long));
>                 if (!area) {
> -                       t->kcov = NULL;
>                         kcov_put(kcov);
>                         return;
>                 }
> @@ -800,7 +799,7 @@ void kcov_remote_start(u64 handle)
>         /* Reset coverage size. */
>         *(u64 *)area = 0;
>
> -       kcov_start(t, size, area, mode, sequence);
> +       kcov_start(t, kcov, size, area, mode, sequence);
>
>  }
>  EXPORT_SYMBOL(kcov_remote_start);
> @@ -873,7 +872,6 @@ void kcov_remote_stop(void)
>                 return;
>
>         kcov_stop(t);
> -       t->kcov = NULL;
>
>         spin_lock(&kcov->lock);
>         /*
> --
> 2.26.0.rc2.310.g2932bb562d-goog
>