linux-kernel - Re: [patch 1/6] perf/core: Remove redundant condition for AUX buffer size

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Message-ID: <9dacc7fa-45c3-40cc-a634-9609c08038e9@lucifer.local>
Date: Thu, 7 Aug 2025 14:30:06 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...uxfoundation.org>,
        Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Kees Cook <kees@...nel.org>
Subject: Re: [patch 1/6] perf/core: Remove redundant condition for AUX buffer
 size

On Wed, Aug 06, 2025 at 10:12:54PM +0200, Thomas Gleixner wrote:
> It is already checked whether the VMA size is the same as
> nr_pages * PAGE_SIZE, so later checking both:

Yeah I see near the start of perf_mmap();

	if (vma_size != PAGE_SIZE * nr_pages)
		return -EINVAL;

>
>       aux_size == vma_size && aux_size == nr_pages * PAGE_SIZE
>
> is redundant. Remove the vma_size check as nr_pages is what is actually
> used in the allocation function. That prepares for splitting out the buffer
> allocation into seperate functions, so that only nr_pages needs to be
> handed in.
>
> No functional change.
>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

So this seems obviously correct:

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>

> ---
>  kernel/events/core.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -7043,7 +7043,7 @@ static int perf_mmap(struct file *file,
>  		if (rb_has_aux(rb) && rb->aux_pgoff != vma->vm_pgoff)
>  			goto aux_unlock;
>
> -		if (aux_size != vma_size || aux_size != nr_pages * PAGE_SIZE)
> +		if (aux_size != nr_pages * PAGE_SIZE)
>  			goto aux_unlock;
>
>  		/* already mapped with a different size */
>