linux-kernel - Re: [PATCH] KVM: PPC: Book3S HV: NULL check before some freeing functions is not needed.

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Date:   Mon, 03 Dec 2018 11:06:50 +1100
From:   Suraj Jitindar Singh <sjitindarsingh@...il.com>
To:     Thomas Meyer <thomas@...3r.de>, paulus@...abs.org,
        benh@...nel.crashing.org, mpe@...erman.id.au,
        kvm-ppc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: PPC: Book3S HV: NULL check before some freeing
 functions is not needed.

On Sun, 2018-12-02 at 21:52 +0100, Thomas Meyer wrote:
> NULL check before some freeing functions is not needed.

Technically true, however I think a comment should be added then to
make it clearer to someone reading the code why this is ok.

See below.

Suraj.

> 
> Signed-off-by: Thomas Meyer <thomas@...3r.de>
> ---
> 
> diff -u -p a/arch/powerpc/kvm/book3s_hv_nested.c
> b/arch/powerpc/kvm/book3s_hv_nested.c
> --- a/arch/powerpc/kvm/book3s_hv_nested.c
> +++ b/arch/powerpc/kvm/book3s_hv_nested.c
> @@ -1252,8 +1252,7 @@ static long int __kvmhv_nested_page_faul
>  	rmapp = &memslot->arch.rmap[gfn - memslot->base_gfn];
>  	ret = kvmppc_create_pte(kvm, gp->shadow_pgtable, pte, n_gpa,
> level,
>  				mmu_seq, gp->shadow_lpid, rmapp,
> &n_rmap);
> -	if (n_rmap)
> -		kfree(n_rmap);
> +	kfree(n_rmap);

e.g.
/* n_rmap set to NULL in kvmppc_create_pte if reference preserved */

>  	if (ret == -EAGAIN)
>  		ret = RESUME_GUEST;	/* Let the guest try
> again */
>