linux-kernel - Re: [6.2][regression] after commit ffcb754584603adf7039d7972564fbf6febdc542 all sound devices disappeared (due BUG at mm/page

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Date:   Fri, 16 Dec 2022 13:15:19 +0100
From:   Christoph Hellwig <hch@....de>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Christoph Hellwig <hch@....de>,
        Mikhail Gavrilov <mikhail.v.gavrilov@...il.com>,
        Takashi Iwai <tiwai@...e.de>, alsa-devel@...a-project.org,
        m.szyprowski@...sung.com,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        iommu@...ts.linux.dev
Subject: Re: [6.2][regression] after commit
 ffcb754584603adf7039d7972564fbf6febdc542 all sound devices
 disappeared (due BUG at mm/page_alloc.c:3592!)

On Fri, Dec 16, 2022 at 11:40:57AM +0000, Robin Murphy wrote:
> On 2022-12-16 06:46, Christoph Hellwig wrote:
>> Ok, it seems like the sound noncontig alloc code that I already
>> commented on as potentially bogus GFP_GOMP mapping trips this.  I think
>> for now the right thing would be to revert the hunk in dma-iommu.c
>> (see patch below).  The other thing to try would be to remove both
>> uses GFP_COMP in sound/core/memalloc.c, which should have the same
>> effect.
>
> Or we explicitly strip the flag in dma_alloc_noncontiguous() (and maybe 
> dma_alloc_pages() as well) for consistency with dma_alloc_attrs(). That 
> seems like it might be the most robust option.

In the long run warning there and returning an error seems like the
right thing to do, yes. I'm just a little worried doing this right now
after the merge window.