linux-kernel - Re: [PATCH v3 1/2] dma-contiguous: Abstract dma_{alloc,free}

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Date:   Wed, 29 May 2019 15:48:07 -0700
From:   Nicolin Chen <nicoleotsuka@...il.com>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     hch@....de, robin.murphy@....com, m.szyprowski@...sung.com,
        vdumpa@...dia.com, linux@...linux.org.uk, catalin.marinas@....com,
        will.deacon@....com, chris@...kel.net, jcmvbkbc@...il.com,
        joro@...tes.org, dwmw2@...radead.org, tony@...mide.com,
        akpm@...ux-foundation.org, sfr@...b.auug.org.au,
        treding@...dia.com, keescook@...omium.org, iamjoonsoo.kim@....com,
        wsa+renesas@...g-engineering.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-xtensa@...ux-xtensa.org, iommu@...ts.linux-foundation.org,
        dann.frazier@...onical.com, clang-built-linux@...glegroups.com
Subject: Re: [PATCH v3 1/2] dma-contiguous: Abstract
 dma_{alloc,free}_contiguous()

Hi Nathan,

On Wed, May 29, 2019 at 11:35:46AM -0700, Nathan Chancellor wrote:
> This commit is causing boot failures in QEMU on x86_64 defconfig:
> 
> https://travis-ci.com/ClangBuiltLinux/continuous-integration/jobs/203825363
> 
> Attached is a bisect log and a boot log with GCC (just to show it is not
> a compiler thing).
> 
> My QEMU command line is:
> 
> qemu-system-x86_64 -m 512m \
>                    -drive file=images/x86_64/rootfs.ext4,format=raw,if=ide \
>                    -append 'console=ttyS0 root=/dev/sda' \
>                    -nographic \
>                    -kernel arch/x86_64/boot/bzImage
> 
> and the rootfs is available here:
> 
> https://github.com/ClangBuiltLinux/continuous-integration/raw/master/images/x86_64/rootfs.ext4

Thanks for reporting the bug.

I am able to repro the issue with the given command and rootfs. The
problem is that x86_64 has CONFIG_DMA_CMA=n so the helper function
is blank on x86_64 while dma-direct should be platform independent.

A simple fix is to add alloc_pages_node() for !CONFIG_DMA_CMA. I'll
submit a fix soon -- need to figure out a good way though. It seems
that adding the fallback to the !CONFIG_DMA_CMA version would cause
some recipe errors when building the kernel...