Re: Deadlock in the routing code

Maxime Henrion wrote:
Julian Elischer wrote:
Gleb Smirnoff wrote:
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?
I think that would be the cleanest way..

So, here's what I've got. I have yet to test it at all, I hope that
I'll be able to do so today, or tomorrow. Any input appreciated.

Cheers,
Maxime


this code is I think (from memory) called only from the user right?
it is possible that on failure to lock one might delay for 1 tick or something..

(I don't have the code in front of me right now)

otherwise I think that might do the job.. more comments later.

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Relevant Pages

  • Re: Deadlock in the routing code
    ... The routed process does its business on the routing socket, ... While in rt_setgateit drops the lock on its ... rtentry in order to call rtalloc1. ... "They that give up essential liberty to obtain temporary safety, ...
    (freebsd-net)
  • Re: Deadlock in the routing code
    ... The routed process does its business on the routing socket, ... While in rt_setgateit drops the lock on its ... rtentry in order to call rtalloc1. ... it's not obvious to me how to fix it :-). ...
    (freebsd-net)
  • Re: Deadlock in the routing code
    ... J> Maxime Henrion wrote: ... J>> holding the lock of the rtentry that the routed process is dealing ... J>> rtentry in order to call rtalloc1. ... J>> lock the gateway route. ...
    (freebsd-net)
  • Re: Deadlock in the routing code
    ... J>> - The routed process does its business on the routing socket, ... J>> rtentry in order to call rtalloc1. ... J>> now tries to re-lock the original rtentry. ... J>> lock the gateway route. ...
    (freebsd-net)
  • Re: Deadlock in the routing code
    ... The routed process does its business on the routing socket, ... While in rt_setgateit drops the lock on its ... rtentry in order to call rtalloc1. ... process hold the gateway route returns it locked), ...
    (freebsd-net)