Deadlock in the routing code
julian at elischer.org
Thu Dec 13 10:47:34 PST 2007
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.
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