linux-kernel - Re: [PATCH] iommu/msm: add a check for the return of kzalloc()

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Date:   Thu, 28 Apr 2022 08:51:30 -0600
From:   Jeffrey Hugo <jeffrey.l.hugo@...il.com>
To:     xkernel.wang@...mail.com
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        MSM <linux-arm-msm@...r.kernel.org>,
        iommu@...ts.linux-foundation.org,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] iommu/msm: add a check for the return of kzalloc()

On Fri, Mar 25, 2022 at 2:13 PM <xkernel.wang@...mail.com> wrote:
>
> From: Xiaoke Wang <xkernel.wang@...mail.com>
>
> kzalloc() is a memory allocation function which can return NULL when
> some internal memory errors happen. So it is better to check it to
> prevent potential wrong memory access.
>
> Signed-off-by: Xiaoke Wang <xkernel.wang@...mail.com>
> ---
>  drivers/iommu/msm_iommu.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/drivers/iommu/msm_iommu.c b/drivers/iommu/msm_iommu.c
> index 3a38352..697ad63 100644
> --- a/drivers/iommu/msm_iommu.c
> +++ b/drivers/iommu/msm_iommu.c
> @@ -597,6 +597,10 @@ static void insert_iommu_master(struct device *dev,
>
>         if (list_empty(&(*iommu)->ctx_list)) {
>                 master = kzalloc(sizeof(*master), GFP_ATOMIC);
> +               if (!master) {
> +                       dev_err(dev, "Failed to allocate iommu_master\n");

How do you reconcile this with chapter 14 of the coding style document?

"These generic allocation functions all emit a stack dump on failure when used
without __GFP_NOWARN so there is no use in emitting an additional failure
message when NULL is returned."

> +                       return;
> +               }
>                 master->of_node = dev->of_node;
>                 list_add(&master->list, &(*iommu)->ctx_list);
>                 dev_iommu_priv_set(dev, master);
> --