linux-kernel - Re: [PATCH] drm/i915/gt: Avoid redundant pointer validity check

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Message-ID: <d58fff32-edad-4a7f-7409-7e57593df3ed@linux.intel.com>
Date:   Mon, 6 Feb 2023 09:45:10 +0000
From:   Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>
To:     Deepak R Varma <drv@...lo.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org,
        Matthew Auld <matthew.auld@...el.com>,
        Thomas Hellstrom <thomas.hellstrom@...el.com>
Cc:     Saurabh Singh Sengar <ssengar@...rosoft.com>,
        Praveen Kumar <kumarpraveen@...ux.microsoft.com>
Subject: Re: [PATCH] drm/i915/gt: Avoid redundant pointer validity check


Hi,

Adding Matt & Thomas as potential candidates to review.

Regards,

Tvrtko

On 03/02/2023 19:30, Deepak R Varma wrote:
> The macro definition of gen6_for_all_pdes() expands to a for loop such
> that it breaks when the page table is null. Hence there is no need to
> again test validity of the page table entry pointers in the pde list.
> This change is identified using itnull.cocci semantic patch.
> 
> Signed-off-by: Deepak R Varma <drv@...lo.com>
> ---
> Please note: Proposed change is compile tested only.
> 
>   drivers/gpu/drm/i915/gt/gen6_ppgtt.c | 5 ++---
>   1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gt/gen6_ppgtt.c b/drivers/gpu/drm/i915/gt/gen6_ppgtt.c
> index 5aaacc53fa4c..787b9e6d9f59 100644
> --- a/drivers/gpu/drm/i915/gt/gen6_ppgtt.c
> +++ b/drivers/gpu/drm/i915/gt/gen6_ppgtt.c
> @@ -258,8 +258,7 @@ static void gen6_ppgtt_free_pd(struct gen6_ppgtt *ppgtt)
>   	u32 pde;
>   
>   	gen6_for_all_pdes(pt, pd, pde)
> -		if (pt)
> -			free_pt(&ppgtt->base.vm, pt);
> +		free_pt(&ppgtt->base.vm, pt);
>   }
>   
>   static void gen6_ppgtt_cleanup(struct i915_address_space *vm)
> @@ -304,7 +303,7 @@ static void pd_vma_unbind(struct i915_address_space *vm,
>   
>   	/* Free all no longer used page tables */
>   	gen6_for_all_pdes(pt, ppgtt->base.pd, pde) {
> -		if (!pt || atomic_read(&pt->used))
> +		if (atomic_read(&pt->used))
>   			continue;
>   
>   		free_pt(&ppgtt->base.vm, pt);