From: Arnd Bergmann <arnd@arndb.de>
To: David Miller <davem@davemloft.net>
Subject: Re: [PATCH] usb/mcs7830: Don't use buffers from stack for USB transfers
Date: Wed, 21 Jan 2009 00:17:18 +0100
User-Agent: KMail/1.9.9
Cc: ceggers@gmx.de, linux-kernel@vger.kernel.org, netdev@vger.kernel.org
References: <34115.192.168.0.40.1232483361.squirrel@server> <200901202345.47792.arnd@arndb.de> <20090120.144719.120709836.davem@davemloft.net>
In-Reply-To: <20090120.144719.120709836.davem@davemloft.net>
MIME-Version: 1.0
Content-Type: text/plain;
  charset="iso-8859-1"
Content-Transfer-Encoding: 8BIT
Content-Disposition: inline
Message-Id: <200901210017.19038.arnd@arndb.de>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1091
Lines: 32

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@arndb.de>
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/