Date: Thu, 13 Dec 2007 10:33:25 -0800 From: Julian Elischer <julian@elischer.org> To: Maxime Henrion <mux@FreeBSD.org> Cc: glebius@FreeBSD.org, net@FreeBSD.org Subject: Re: Deadlock in the routing code Message-ID: <47617AF5.7070701@elischer.org> In-Reply-To: <20071213133817.GC71713@elvis.mu.org> References: <20071213133817.GC71713@elvis.mu.org>
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Maxime Henrion wrote: > Replying to myself on this one, sorry about that. > > I said in my previous mail that I didn't know yet what process was > holding the lock of the rtentry that the routed process is dealing > with in rt_setgate(), and I just could verify that it is held by > the swi1: net thread. > > So, in a nutshell: > > - The routed process does its business on the routing socket, that ends up > calling rt_setgate(). While in rt_setgate() it drops the lock on its > rtentry in order to call rtalloc1(). At this point, the routed > process hold the gateway route (rtalloc1() returns it locked), and it > now tries to re-lock the original rtentry. > - At the same time, the swi net thread calls arpresolve() which ends up > calling rt_check(). Then rt_check() locks the rtentry, and tries to > lock the gateway route. > > A classical case of deadlock with mutexes because of different locking > order. Now, it's not obvious to me how to fix it :-). On failure to re-lock, the routed call to rt_setgate should completely abort and restart from scratch, releasing all locks it has on the way out. > Maxime > _______________________________________________ > freebsd-net@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-net > To unsubscribe, send any mail to "freebsd-net-unsubscribe@freebsd.org"
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