How is supposed to be protected the units list?

[Scott Long]

On Mar 21, 2010, at 10:02 AM, Attilio Rao wrote:

> 2010/3/21 Alexander Motin <mav at freebsd.org>:
>> Attilio Rao wrote:
>>> So I made this new patch using the bus lock:
>>> http://www.freebsd.org/~attilio/Sandvine/pdrv/xpt_lock.diff
>> 
>> OK. I've looked on both and I think both have race window between unit
>> number allocation and insertion into the list. I've changed last patch
>> to not drop the lock in meantime. What do you think about this:
>> http://people.freebsd.org/~mav/unit_lock.patch
>> ?
>> 
>> Part about scsi_da.c I don't like in both cases, as I am not sure that
>> locks can't be recursed there in case of some errors. I don't see how
>> adding second lock could solve it.
> 
> I think that we should protect there in anyway.
> Probabilly we may cache the list and refcount the periphs? (then
> unlock the lock and just do the lockless operation in order to avoid
> recursion?)
> The race handling for units allocation is fine, thanks.
> 

Please give me a few more days to review and comment on this.  Alexander's change is very invasive in that it re-orders operations, and I'd like to review it to ensure that that doesn't break existing ordering assumptions.

Scott