Re: PATCH (for comment): ide-cd possible race in PIO mode

[Jens Axboe <axboe@suse.de>]

On Wed, Nov 17 2004, Jens Axboe wrote:
> On Wed, Nov 17 2004, Alan Cox wrote:
> > Working on tracing down Fedora bug #115458
> > (https://bugzilla.redhat.com/bugzilla/process_bug.cgi) I found what
> > appears to be a race between the IDE CD driver and the hardware status.
> > It doesn't appear to explain the bug at all but it does look like a bug
> > of itself
> > 
> > When we issue an ide command the status bits don't become valid for
> > 400nS. In the DMA case ide_execute_command handles this but in the PIO
> > case we don't do the needed locking, use OUTBSYNC to avoid posting or
> > delay. This means that in some situations we can execute the command
> > handler in PIO mode before the command status bits are valid and the
> > handler may read and act wrongly.
> > 
> > --- drivers/ide/ide-cd.c~	2004-11-17 14:08:42.950485320 +0000
> > +++ drivers/ide/ide-cd.c	2004-11-17 14:08:42.951485168 +0000
> > @@ -897,7 +897,10 @@
> >  		return ide_started;
> >  	} else {
> >  		/* packet command */
> > -		HWIF(drive)->OUTB(WIN_PACKETCMD, IDE_COMMAND_REG);
> > +		spin_lock_irqsave(&ide_lock, flags);
> > +		HWIF(drive)->OUTBSYNC(WIN_PACKETCMD, IDE_COMMAND_REG);
> > +		ndelay(400);
> > +		spin_unlock_irqsave(&ide_lock, flags);
> >  		return (*handler) (drive);
> >  	}

btw alan, have you attempted to compile this? It averages 2 errors out
of 4 lines :)

-- 
Jens Axboe