Re: [PATCH 4/5] kcov: Avoid enable+disable interrupts if !in_task().

From: Dmitry Vyukov
Date: Fri Sep 17 2021 - 10:50:59 EST


On Mon, 30 Aug 2021 at 19:26, Sebastian Andrzej Siewior
<bigeasy@xxxxxxxxxxxxx> wrote:
>
> kcov_remote_start() may need to allocate memory in the in_task() case
> (otherwise per-CPU memory has been pre-allocated) and therefore requires
> enabled interrupts.
> The interrupts are enabled before checking if the allocation is required
> so if no allocation is required then the interrupts are needlessly
> enabled and disabled again.
>
> Enable interrupts only if memory allocation is performed.
>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>

Acked-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>

> ---
> kernel/kcov.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/kcov.c b/kernel/kcov.c
> index 4f910231d99a2..620dc4ffeb685 100644
> --- a/kernel/kcov.c
> +++ b/kernel/kcov.c
> @@ -869,19 +869,19 @@ void kcov_remote_start(u64 handle)
> size = CONFIG_KCOV_IRQ_AREA_SIZE;
> area = this_cpu_ptr(&kcov_percpu_data)->irq_area;
> }
> - spin_unlock_irqrestore(&kcov_remote_lock, flags);
> + spin_unlock(&kcov_remote_lock);
>
> /* Can only happen when in_task(). */
> if (!area) {
> + local_irqrestore(flags);
> area = vmalloc(size * sizeof(unsigned long));
> if (!area) {
> kcov_put(kcov);
> return;
> }
> + local_irq_save(flags);
> }
>
> - local_irq_save(flags);
> -
> /* Reset coverage size. */
> *(u64 *)area = 0;
>
> --
> 2.33.0
>