Re: [PATCH 6/7] ALSA: memalloc: don't pass bogus GFP_ flags to dma_alloc_*

From: Takashi Iwai <tiwai@suse.de>
To: Christoph Hellwig <hch@lst.de>
Cc: Dennis Dalessandro <dennis.dalessandro@cornelisnetworks.com>,
	Mauro Carvalho Chehab <mchehab@kernel.org>,
	Alexandra Winter <wintera@linux.ibm.com>,
	Wenjia Zhang <wenjia@linux.ibm.com>,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	Jaroslav Kysela <perex@perex.cz>, Takashi Iwai <tiwai@suse.com>,
	Russell King <linux@armlinux.org.uk>,
	Robin Murphy <robin.murphy@arm.com>,
	linux-arm-kernel@lists.infradead.org, linux-rdma@vger.kernel.org,
	iommu@lists.linux.dev, linux-media@vger.kernel.org,
	netdev@vger.kernel.org, linux-s390@vger.kernel.org,
	alsa-devel@alsa-project.org
Subject: Re: [PATCH 6/7] ALSA: memalloc: don't pass bogus GFP_ flags to dma_alloc_*
Date: Mon, 14 Nov 2022 10:04:37 +0100	[thread overview]
Message-ID: <87leod52l6.wl-tiwai@suse.de> (raw)
In-Reply-To: <20221113163535.884299-7-hch@lst.de>

On Sun, 13 Nov 2022 17:35:34 +0100,
Christoph Hellwig wrote:
> 
> dma_alloc_coherent/dma_alloc_wc is an opaque allocator that only uses
> the GFP_ flags for allocation context control.  Don't pass __GFP_COMP
> which makes no sense for an allocation that can't in any way be
> converted to a page pointer.

The addition of __GFP_COMP there was really old, it was Hugh's commit
f3d48f0373c1 at 2005:
    [PATCH] unpaged: fix sound Bad page states

It mentions something about sparc32/64.  I hope this isn't relevant
any longer (honestly I have no idea about that).

> Note that for dma_alloc_noncoherent and dma_alloc_noncontigous in
> combination with the DMA mmap helpers __GFP_COMP looks sketchy as well,
> so I would suggest to drop that as well after a careful audit.

Yeah, that's a cargo-cult copy&paste from the old idiom.
Should be killed altogether.

Thanks!

Takashi