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Date:      Tue, 21 Jun 2005 13:31:50 +0400
From:      Gleb Smirnoff <glebius@FreeBSD.org>
To:        Jeremie Le Hen <jeremie@le-hen.org>
Cc:        freebsd-stable@FreeBSD.org
Subject:   Re: panic in RELENG_5 UMA
Message-ID:  <20050621093150.GA35316@cell.sick.ru>
In-Reply-To: <20050621092836.GD738@obiwan.tataz.chchile.org>
References:  <20050621070427.GA738@obiwan.tataz.chchile.org> <20050621090701.GB34406@cell.sick.ru> <20050621092836.GD738@obiwan.tataz.chchile.org>

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On Tue, Jun 21, 2005 at 11:28:36AM +0200, Jeremie Le Hen wrote:
J> > IMHO, this looks like a race. The route is not locked, when
J> > its llinfo is edited.
J> > 
J> > Probably the mbuf was freed when arp reply arrived and la_hold was send.
J> > Look into in_arpinput() near 736:
J> > 
J> >                         (*ifp->if_output)(ifp, la->la_hold, rt_key(rt), rt);
J> >                         la->la_hold = 0;
J> > 
J> > Yeah, I have just triggered another panic running 15 instances of this
J> > script on SMP box:
J> > 
J> > (
J> > while (true); do
J> > 	arp -d 81.19.64.111  >/dev/null 2>&1;
J> > 	ping -c 1 -t 1 81.19.64.111 >/dev/null 2>&1;
J> > done
J> > ) &
J> > 
J> > But my duplicate free is in fxp_txeof(). This means that output thread has
J> > won the race.
J> 
J> This explanation sounds good but my box is an UP with PREEMPTION.
J> Is is supposed to be also possible in this case ?

I guess yes, because of preemption.

-- 
Totus tuus, Glebius.
GLEBIUS-RIPN GLEB-RIPE



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