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Subject: Removing queue length check in ip_output (was Re: buf_ring in HEAD is
racy)
From: Adrian Chadd <adrian@freebsd.org>
To: Ryan Stone <rysto32@gmail.com>
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Cc: Jack F Vogel <jfv@freebsd.org>,
Michael Tuexen <Michael.Tuexen@lurchi.franken.de>,
freebsd-net <freebsd-net@freebsd.org>
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How about we can this check in ip_output():
/*
* Verify that we have any chance at all of being able to queue the
* packet or packet fragments, unless ALTQ is enabled on the given
* interface in which case packetdrop should be done by queueing.
*/
n = ip_len / mtu + 1; /* how many fragments ? */
if (
#ifdef ALTQ
(!ALTQ_IS_ENABLED(&ifp->if_snd)) &&
#endif /* ALTQ */
(ifp->if_snd.ifq_len + n) >= ifp->if_snd.ifq_maxlen ) {
error = ENOBUFS;
IPSTAT_INC(ips_odropped);
ifp->if_snd.ifq_drops += n;
goto bad;
}
.. it's totally bogus in an if_transmit / SMP world. There's no
locking and there's no guarantee that there will be headroom in the
queue between this point and the later call to the if_output() method.
-adrian