linux-kernel - Re: remove dma_zalloc

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Message-ID: <alpine.DEB.2.20.1901081456370.6130@hadrien>
Date:   Tue, 8 Jan 2019 14:56:59 +0100 (CET)
From:   Julia Lawall <julia.lawall@...6.fr>
To:     Christoph Hellwig <hch@....de>
cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Luis Chamberlain <mcgrof@...nel.org>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: remove dma_zalloc_coherent



On Tue, 8 Jan 2019, Julia Lawall wrote:

>
>
> On Tue, 8 Jan 2019, Christoph Hellwig wrote:
>
> > Hi Linus and world,
> >
> > We've always had a weird situation around dma_zalloc_coherent.  To
> > safely support mapping the allocations to userspace major architectures
> > like x86 and arm have always zeroed allocations from dma_alloc_coherent,
> > but a couple other architectures were missing that zeroing either always
> > or in corner cases.  Then later we grew anothe dma_zalloc_coherent
> > interface to explicitly request zeroing, but that just added __GFP_ZERO
> > to the allocation flags, which for some allocators that didn't end
> > up using the page allocator ended up being a no-op and still not
> > zeroing the allocations.
> >
> > So for this merge window I fixed up all remaining architectures to zero
> > the memory in dma_alloc_coherent, and made dma_zalloc_coherent a no-op
> > wrapper around dma_alloc_coherent, which fixes all of the above issues.
> >
> > dma_zalloc_coherent is now pointless and can go away, and Luis helped
> > me writing a cocchinelle script and patch series to kill it, which I
> > think we should apply now just after -rc1 to finally settle these
> > issue.
> >
> > The script that generated the first patch is included here:
> >
> > @ replace_dma_zalloc_coherent @
> > expression dev, size, data, handle, flags;
> > @@
> >
> > -dma_zalloc_coherent(dev, size, handle, flags)
> > +dma_alloc_coherent(dev, size, handle, flags)
>
> Great.  We should also update api/alloc/zalloc-simple.cocci.  The message
> could just say that the z version is no longer needed.

Oops, I see that you already took care of it.  Thanks!

julia