linux-kernel - Re: [PATCH] b43: fix regression in PIO case

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Date:	Wed, 28 Dec 2011 01:00:55 +0100 (CET)
From:	Guennadi Liakhovetski <g.liakhovetski@....de>
To:	Larry Finger <Larry.Finger@...inger.net>
cc:	Rafał Miłecki <zajec5@...il.com>,
	linux-wireless@...r.kernel.org,
	"John W. Linville" <linville@...driver.com>,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] b43: fix regression in PIO case

On Tue, 27 Dec 2011, Larry Finger wrote:

> On 12/27/2011 05:05 PM, Guennadi Liakhovetski wrote:
> > On Tue, 27 Dec 2011, Rafał Miłecki wrote:
> > 
> > > W dniu 26 grudnia 2011 18:28 użytkownik Guennadi Liakhovetski
> > > <g.liakhovetski@....de>  napisał:
> > > > This patch fixes the regression, introduced by
> > > > 
> > > > commit 17030f48e31adde5b043741c91ba143f5f7db0fd
> > > > From: Rafał Miłecki<zajec5@...il.com>
> > > > Date: Thu, 11 Aug 2011 17:16:27 +0200
> > > > Subject: [PATCH] b43: support new RX header, noticed to be used in
> > > > 598.314+ fw
> > > > 
> > > > in PIO case.
> > > > 
> > > > Signed-off-by: Guennadi Liakhovetski<g.liakhovetski@....de>
> > > > ---
> > > > diff --git a/drivers/net/wireless/b43/pio.c
> > > > b/drivers/net/wireless/b43/pio.c
> > > > index ce8a4bd..b64b64c 100644
> > > > --- a/drivers/net/wireless/b43/pio.c
> > > > +++ b/drivers/net/wireless/b43/pio.c
> > > > @@ -617,9 +617,19 @@ static bool pio_rx_frame(struct b43_pio_rxqueue *q)
> > > >         const char *err_msg = NULL;
> > > >         struct b43_rxhdr_fw4 *rxhdr =
> > > >                 (struct b43_rxhdr_fw4 *)wl->pio_scratchspace;
> > > > +       size_t rxhdr_size = sizeof(*rxhdr);
> > > > 
> > > >         BUILD_BUG_ON(sizeof(wl->pio_scratchspace)<  sizeof(*rxhdr));
> > > > -       memset(rxhdr, 0, sizeof(*rxhdr));
> > > > +       switch (dev->fw.hdr_format) {
> > > > +       case B43_FW_HDR_410:
> > > > +       case B43_FW_HDR_351:
> > > > +               rxhdr_size -= sizeof(rxhdr->format_598) -
> > > > +                       sizeof(rxhdr->format_351);
> > > > +               break;
> > > > +       case B43_FW_HDR_598:
> > > > +               break;
> > > > +       }
> > > > +       memset(rxhdr, 0, rxhdr_size);
> > > 
> > > Huuh, that's really tricky. Can you just do "normal" conditions as
> > > Larry suggested, please?
> > 
> > Sorry? I absolutely see nothing tricky there. Do you think this would look
> > "less tricky" to you:
> > 
> > 	switch (dev->fw.hdr_format) {
> > 	case B43_FW_HDR_410:
> > 	case B43_FW_HDR_351:
> > 		rxhdr_size = offsetof(struct b43_rxhdr_fw4,
> > 					format_351) +
> > 			sizeof(rxhdr_size->format_351);
> > 		break;
> > 	case B43_FW_HDR_598:
> > 		rxhdr_size = sizeof(*rxhdr);
> > 		break;
> > 	}
> > 
> 
> How about this?
> 
> Index: wireless-testing-new/drivers/net/wireless/b43/pio.c
> ===================================================================
> --- wireless-testing-new.orig/drivers/net/wireless/b43/pio.c
> +++ wireless-testing-new/drivers/net/wireless/b43/pio.c
> @@ -617,9 +617,20 @@ static bool pio_rx_frame(struct b43_pio_
>         const char *err_msg = NULL;
>         struct b43_rxhdr_fw4 *rxhdr =
>                 (struct b43_rxhdr_fw4 *)wl->pio_scratchspace;
> +       size_t rxhdr_size;
> 
>         BUILD_BUG_ON(sizeof(wl->pio_scratchspace) < sizeof(*rxhdr));
> -       memset(rxhdr, 0, sizeof(*rxhdr));
> +       switch (dev->fw.hdr_format) {
> +       case B43_FW_HDR_410:
> +       case B43_FW_HDR_351:
> +               rxhdr_size = sizeof(rxhdr->format_351);
> +               break;
> +       case B43_FW_HDR_598:
> +       default:
> +               rxhdr_size = sizeof(rxhdr->format_598);
> +               break;
> +       }
> +       memset(rxhdr, 0, rxhdr_size);
> 
>         /* Check if we have data and wait for it to get ready. */
>         if (q->rev >= 8) {

I am sorry, I'm either being blind and stupid or you're trying to do 
something quite wrong there. struct b43_rxhdr_fw4 has a bunch of fields 
first, then at the end it has a union of two fields: format_598 and 
format_351, right? rxhdr is pointing at the struct itself. Before the 
offending patch memset() used to clean the whole struct. Now in your above 
version you calculate the size of one of those union fields and nullify 
that many bytes from the _beginning_ of the whole struct.

I've seen myself being wrong before, but here... I'll let you judge 
though.

Thanks
Guennadi
---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/
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