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Date:      Tue, 07 Jan 2003 13:58:10 -0700 (MST)
From:      "M. Warner Losh" <imp@bsdimp.com>
To:        gallatin@cs.duke.edu
Cc:        tlambert2@mindspring.com, nate@root.org, current@FreeBSD.ORG, net@FreeBSD.ORG
Subject:   Re: Proper -current if_attach locking?
Message-ID:  <20030107.135810.92265343.imp@bsdimp.com>
In-Reply-To: <15899.6077.710661.497492@grasshopper.cs.duke.edu>
References:  <15898.60467.681434.927797@grasshopper.cs.duke.edu> <20030107.105933.19259527.imp@bsdimp.com> <15899.6077.710661.497492@grasshopper.cs.duke.edu>

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In message: <15899.6077.710661.497492@grasshopper.cs.duke.edu>
            Andrew Gallatin <gallatin@cs.duke.edu> writes:
: 
: M. Warner Losh writes:
:  > In message: <15898.60467.681434.927797@grasshopper.cs.duke.edu>
:  >             Andrew Gallatin <gallatin@cs.duke.edu> writes:
:  > : The IFNET_RLOCK() called in if_slowtimo() is a global lock for the
:  > : list of ifnet structs to ensure that no devices are removed or added
:  > : while something may be using it.  There is one ifnet list in the system.
:  > 
:  > So this means that only the locking in attach is bogus, and similar
:  > locking in detach is also bogus because they produce lock order
:  > reversals as the global lock is held to insert/remove if interfaces.
: 
: Yes.  Though I haven't looked at if_dc myself, there may be other
: locking problems.  I've only been commenting on the ones that you
: brought up.
: 
: But back to an earlier point.  Somebody (you?) validly pointed out
: that the driver should not be callable and should not generate
: interrupts until its finished attaching.  The lock in its attach was
: probably a somewhat misguided attempt at that.  

Yes.  That was me.  There are some drivers that have separated
front/back ends that makes this harder, but most of them don't.

: The first point can be accomplished by doing the ether_ifattach()
: last, but the second may be harder.  I do that by poking a bit on my
: card which prevents it from generating interrupts while the device is
: being setup.  Not sure if a similar bit exists on tulip cards.

All PCI cards have to be able to turn off their interrupt sources,
otherwise interrupt storms result.  At least that's my understanding.

Warner

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