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Date:      Fri, 12 Mar 2010 20:29:12 +0100
From:      Attilio Rao <attilio@freebsd.org>
To:        Alexander Motin <mav@freebsd.org>
Cc:        freebsd-scsi@freebsd.org, "Justin T. Gibbs" <gibbs@freebsd.org>, mj@feral.com
Subject:   Re: How is supposed to be protected the units list?
Message-ID:  <3bbf2fe11003121129w69b6e48xfc3982bd9016bcce@mail.gmail.com>
In-Reply-To: <4B9A91DA.7030107@FreeBSD.org>
References:  <3bbf2fe11002281655i61a5f0a0if3f381ad0c4a1ef8@mail.gmail.com> <3bbf2fe11003031532u2207eb55h19c3a045215a7d84@mail.gmail.com> <4B8EF336.80107@feral.com> <3bbf2fe11003031547kd5f7314t3d83b2bde06c1c2f@mail.gmail.com> <4B8EF990.5030407@feral.com> <3bbf2fe11003031607wa3727b5ke89bc2a909d4d6a6@mail.gmail.com> <4B901419.8060800@feral.com> <3bbf2fe11003041737p30690522ya81e1b8f4bd6bbf9@mail.gmail.com> <3bbf2fe11003120601y3c403a1ct50f9fc6c1f0903bf@mail.gmail.com> <4B9A91DA.7030107@FreeBSD.org>

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2010/3/12 Alexander Motin <mav@freebsd.org>:
> Attilio Rao wrote:
>> 2010/3/5 Attilio Rao <attilio@freebsd.org>:
>>> 2010/3/4 Matthew Jacob <mj@feral.com>:
>>>> The referred to patch at least got me out of panic case :-)..
>>>>
>>>> http://people.freebsd.org/~mjacob/scsi_da.c.patch
>>> Yes, honestly the main intent of this patch is to offer a stable
>>> ground for correct handling of periph. When looking about refcounting
>>> them correctly, the main problem is that there was no initial
>>> condition assuring safety, and the initial patch should address this,
>>> but I'm sure there are places where periph refcount is not handled
>>> correctly and this may be one.
>>
>> So, as long as it seems nobody had a strong argument against this
>> patch, what do you think about me committing it?
>> We can further refine later if we think it is the case.
>>
>> Also, I think that Matt's patch should be committed just after this
>> one (and possibly we should investigate a similar add-on for the ata
>> counterpart too?).
>
> I have already told my opinion, that second lock may be not needed. I
> would like to think a bit more about both patches after getting back
> from the conference. Thanks,

If you don't want to use the second lock, you have to use xpt_lock in
all the other places anyways.
I think it can get messy in particular if linked to another aspect:
Another question, may be to integrate that locking paradigm directly
with reference count of periph.
It depends by if the periph can came from other parts as well.

Attilio


-- 
Peace can only be achieved by understanding - A. Einstein



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