Date: Fri, 14 Dec 2007 12:25:39 +0300 From: Gleb Smirnoff <glebius@FreeBSD.org> To: Julian Elischer <julian@elischer.org> Cc: Maxime Henrion <mux@FreeBSD.org>, net@FreeBSD.org Subject: Re: Deadlock in the routing code Message-ID: <20071214092539.GB14339@glebius.int.ru> In-Reply-To: <47617AF5.7070701@elischer.org> References: <20071213133817.GC71713@elvis.mu.org> <47617AF5.7070701@elischer.org>
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On Thu, Dec 13, 2007 at 10:33:25AM -0800, Julian Elischer wrote: J> Maxime Henrion wrote: J> > Replying to myself on this one, sorry about that. J> > I said in my previous mail that I didn't know yet what process was J> > holding the lock of the rtentry that the routed process is dealing J> > with in rt_setgate(), and I just could verify that it is held by J> > the swi1: net thread. J> > So, in a nutshell: J> > - The routed process does its business on the routing socket, that ends up J> > calling rt_setgate(). While in rt_setgate() it drops the lock on its J> > rtentry in order to call rtalloc1(). At this point, the routed J> > process hold the gateway route (rtalloc1() returns it locked), and it J> > now tries to re-lock the original rtentry. J> > - At the same time, the swi net thread calls arpresolve() which ends up J> > calling rt_check(). Then rt_check() locks the rtentry, and tries to J> > lock the gateway route. J> > A classical case of deadlock with mutexes because of different locking J> > order. Now, it's not obvious to me how to fix it :-). J> J> On failure to re-lock, the routed call to rt_setgate should completely abort J> and restart from scratch, releasing all locks it has on the way out. Do you suggest mtx_trylock? -- Totus tuus, Glebius. GLEBIUS-RIPN GLEB-RIPE
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