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Date: Sun, 21 Oct 2012 21:43:16 -0400
Message-ID: <CAFMmRNxNMBAZ1fPKox4Y4rJhhh0AjSXwxCvrVbG89sOyohd7zQ@mail.gmail.com>
Subject: Re: ixgbe & if_igb RX ring locking
From: Ryan Stone <rysto32@gmail.com>
To: "Alexander V. Chernikov" <melifaro@freebsd.org>
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Cc: Jack Vogel <jfvogel@gmail.com>, net@freebsd.org
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On Sun, Oct 21, 2012 at 2:21 PM, Alexander V. Chernikov
<melifaro@freebsd.org> wrote:
>> ix:rx ->  udp is also fairly obvious (here's one backtrace):
> The same question, where "udp" -> "ix:rx" can happen ?

It can't happen directly as far as I can tell.  But to trigger a
deadlock, "all" that has to happen is that a thread holds each mutex
in the cycle while trying to acquire the next mutex in the cycle.  I
realize that in this case that requires five separate threads to all
lose a race simultaneously, but it's still theoretically possible and
needs to be avoided.