netdev - Re: [PATCH 2/7] RDMA/hfi1: don't pass bogus GFP_ flags to dma_alloc

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Date:   Wed, 16 Nov 2022 08:40:18 -0600
From:   Dean Luick <dean.luick@...nelisnetworks.com>
To:     Christoph Hellwig <hch@....de>,
        Dennis Dalessandro <dennis.dalessandro@...nelisnetworks.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Alexandra Winter <wintera@...ux.ibm.com>,
        Wenjia Zhang <wenjia@...ux.ibm.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Russell King <linux@...linux.org.uk>,
        Robin Murphy <robin.murphy@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-rdma@...r.kernel.org,
        iommu@...ts.linux.dev, linux-media@...r.kernel.org,
        netdev@...r.kernel.org, linux-s390@...r.kernel.org,
        alsa-devel@...a-project.org
Subject: Re: [PATCH 2/7] RDMA/hfi1: don't pass bogus GFP_ flags to
 dma_alloc_coherent

On 11/13/2022 10:35 AM, Christoph Hellwig wrote:
> dma_alloc_coherent is an opaque allocator that only uses the GFP_ flags
> for allocation context control.  Don't pass GFP_USER which doesn't make
> sense for a kernel DMA allocation or __GFP_COMP which makes no sense
> for an allocation that can't in any way be converted to a page pointer.
>
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>  drivers/infiniband/hw/hfi1/init.c | 21 +++------------------
>  1 file changed, 3 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/infiniband/hw/hfi1/init.c b/drivers/infiniband/hw/hfi1/init.c
> index 436372b314312..24c0f0d257fc9 100644
> --- a/drivers/infiniband/hw/hfi1/init.c
> +++ b/drivers/infiniband/hw/hfi1/init.c
> @@ -1761,17 +1761,11 @@ int hfi1_create_rcvhdrq(struct hfi1_devdata *dd, struct hfi1_ctxtdata *rcd)
>       unsigned amt;
>
>       if (!rcd->rcvhdrq) {
> -             gfp_t gfp_flags;
> -
>               amt = rcvhdrq_size(rcd);
>
> -             if (rcd->ctxt < dd->first_dyn_alloc_ctxt || rcd->is_vnic)
> -                     gfp_flags = GFP_KERNEL;
> -             else
> -                     gfp_flags = GFP_USER;
>               rcd->rcvhdrq = dma_alloc_coherent(&dd->pcidev->dev, amt,
>                                                 &rcd->rcvhdrq_dma,
> -                                               gfp_flags | __GFP_COMP);
> +                                               GFP_KERNEL);

A user context receive header queue may be mapped into user space.  Is that not the use case for GFP_USER?  The above conditional is what decides.

Why do you think GFP_USER should be removed here?

-Dean
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