Re: FWD: [BK PATCH] SCSI host num allocation improvement

[Ben Collins <bcollins@debian.org>]

On Fri, Feb 27, 2004 at 09:29:34AM -0600, James Bottomley wrote:
> On Fri, 2004-02-27 at 09:15, Ben Collins wrote:
> > If a driver somehow removes it's scsi host and then later attempts a
> > scsi_host_lookup for the id, I think that driver is broken anyway. IOW,
> > it is safe as long as you aren't broken in the first place.
> 
> I'm not thinking about the driver, I'm thinking about the hotplug
> system.  Hotplug events are queued and not locked.  The event identifies
> the scsi device by the (host number, channel number, target, lun)
> quadruple.  The reason it has to do that is that the /proc/scsi/scsi
> add/remove device operate on these numbers.
> 
> If we get a sequence of racing connects and disconnects, we could mis
> identify the devices because of the host number reuse.  That's the race
> I want assurance of making safe if we move to reusing the numbers.
> 
> Obviously, one solution would be to fix the /proc add/remove, but it's a
> bit late in 2.6 to change the interface, I think.

On the same token, if you hot plug/unplug a single device (not a host)
on the same host, you will already have this problem. This wont make the
problem any worse or better. Devices are more likely to get
plugged/unplugged anyway (well, in the case of usb/firewire you
plug/unplug a host/dev combination, but still).

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