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Date: Wed, 31 Aug 2011 19:46:22 +0300
From: Andriy Gapon <avg@FreeBSD.org>
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To: Warner Losh <imp@bsdimp.com>
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Cc: Hans Petter Selasky <hselasky@FreeBSD.org>, John Baldwin <jhb@FreeBSD.org>,
	freebsd-arch@FreeBSD.org
Subject: Re: skipping locks, mutex_owned, usb
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on 31/08/2011 19:32 Warner Losh said the following:
> 
> On Aug 31, 2011, at 10:13 AM, Andriy Gapon wrote:
>> So why the mutex unwinding/rewinding code is present at all?
>> What kind of situations is it supposed to prevent?
>>
>> Personally I think that we either know that those drivers should not hold the
>> locks in question (bus_mtx and xfer_mtx) or we know that they hold them.
>> I do not see why we have to be conditional here or have a loop even...
> 
> Today, I think we know these things.  In the past, as the code was written, there was a lot more special case code needed for giant cohabitation.

Since you chimed in... :-)
I have a hard time imagining a situation where that code is useful today or was
useful before.
Any example, purely hypothetical even, would do.


-- 
Andriy Gapon