linux-kernel - Re: [PATCH v14 06/12] swiotlb: Use is_swiotlb_force

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Message-ID: <CALiNf288ZLMhY3E8E3N+z9rkwi1viWNLm1wwMEwT4rNwh3FfwQ@mail.gmail.com>
Date:   Thu, 24 Jun 2021 14:05:39 +0800
From:   Claire Chang <tientzu@...omium.org>
To:     Christoph Hellwig <hch@....de>
Cc:     Qian Cai <quic_qiancai@...cinc.com>, Will Deacon <will@...nel.org>,
        Rob Herring <robh+dt@...nel.org>, mpe@...erman.id.au,
        Joerg Roedel <joro@...tes.org>,
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        Robin Murphy <robin.murphy@....com>, bauerman@...ux.ibm.com
Subject: Re: [PATCH v14 06/12] swiotlb: Use is_swiotlb_force_bounce for
 swiotlb data bouncing

On Thu, Jun 24, 2021 at 1:43 PM Christoph Hellwig <hch@....de> wrote:
>
> On Wed, Jun 23, 2021 at 02:44:34PM -0400, Qian Cai wrote:
> > is_swiotlb_force_bounce at /usr/src/linux-next/./include/linux/swiotlb.h:119
> >
> > is_swiotlb_force_bounce() was the new function introduced in this patch here.
> >
> > +static inline bool is_swiotlb_force_bounce(struct device *dev)
> > +{
> > +     return dev->dma_io_tlb_mem->force_bounce;
> > +}
>
> To me the crash looks like dev->dma_io_tlb_mem is NULL.  Can you
> turn this into :
>
>         return dev->dma_io_tlb_mem && dev->dma_io_tlb_mem->force_bounce;
>
> for a quick debug check?

I just realized that dma_io_tlb_mem might be NULL like Christoph
pointed out since swiotlb might not get initialized.
However,  `Unable to handle kernel paging request at virtual address
dfff80000000000e` looks more like the address is garbage rather than
NULL?
I wonder if that's because dev->dma_io_tlb_mem is not assigned
properly (which means device_initialize is not called?).