linux-kernel - Re: [PATCH v2] usb: core: warn if a GFP zone flag is passed to hcd_buffer

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Message-ID: <522b3049-8e7f-41d4-a811-3385992a4d46@suse.com>
Date: Tue, 15 Apr 2025 09:53:24 +0200
From: Oliver Neukum <oneukum@...e.com>
To: Petr Tesarik <ptesarik@...e.com>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] usb: core: warn if a GFP zone flag is passed to
 hcd_buffer_alloc()

On 14.04.25 09:02, Petr Tesarik wrote:

Hi,
  
> That's the point. AFAICS there are _no_ in-tree callers that would pass
> GFP_DMA or GFP_DMA32 to hcd_buffer_alloc(), directly or indirectly. But
> nobody should be tempted to add the flag, because I cannot imagine how
> that would ever be the right thing to do.

You do not dream about putting USB onto PCMCIA over Thunderbolt?

> I can change it back to mem_flags &= ~GFP_ZONEMASK to fix it silently;
> I simply thought that driver authors may appreciate a warning that
> they're trying to do something silly.

People rarely appreciate warnings. I think we should limit them
to cases where something goes wrong or something unexpected happens.

> Whatever works for you, but please keep in mind that there seems to be
> agreement among mm people that DMA and DMA32 zones should be removed
> from the kernel eventually.

Well, if somebody finds a legitimate use case for these flags, the mm
people should deal with it. They are likelier to find a good solution than
all driver writers being forced into finding individual solutions.

	Regards
		Oliver