linux-kernel - Re: [PATCH] usb/mcs7830: Don't use buffers from stack for USB transfers

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Message-Id: <200901210017.19038.arnd@arndb.de>
Date:	Wed, 21 Jan 2009 00:17:18 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	David Miller <davem@...emloft.net>
Cc:	ceggers@....de, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH] usb/mcs7830: Don't use buffers from stack for USB transfers

On Tuesday 20 January 2009, David Miller wrote:
> You cannot DMA from/to the kernel stack, because it might not be in
> the aliased linear mapping of physical memory.  It could even be
> vmalloc()'d memory on some platforms.

Ok, I see. It seems a bit of a waste to do a kmalloc for something
that is guaranteed to be just a few bytes, but allocating the
buffer per-device would mean another mutex, which has about the
same overhead, so I'm basically ok with the patch.

> +       buffer = kmalloc(size, GFP_NOIO);

GFP_NOIO seems out of place in a network driver: there is nothing
wrong with waiting for I/O here, so plain GFP_KERNEL should be fine.

> +       if (buffer == NULL)
> +               return -ENOMEM;

I'd prefer to write 

	if (!buffer)

here, as I do elsewhere in the driver.

Otherwise,

Acked-by: Arnd Bergmann <arnd@...db.de>
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