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Date: Wed, 13 Apr 2022 10:14:22 -0700 From: Eric Dumazet <edumazet@...gle.com> To: David Howells <dhowells@...hat.com> Cc: netdev@...r.kernel.org, Marc Dionne <marc.dionne@...istor.com>, linux-afs@...ts.infradead.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH net] rxrpc: Restore removed timer deletion On Wed, Apr 13, 2022 at 3:16 AM David Howells <dhowells@...hat.com> wrote: > > A recent patch[1] from Eric Dumazet flipped the order in which the > keepalive timer and the keepalive worker were cancelled in order to fix a > syzbot reported issue[2]. Unfortunately, this enables the mirror image bug > whereby the timer races with rxrpc_exit_net(), restarting the worker after > it has been cancelled: > > CPU 1 CPU 2 > =============== ===================== > if (rxnet->live) > <INTERRUPT> > rxnet->live = false; > cancel_work_sync(&rxnet->peer_keepalive_work); > rxrpc_queue_work(&rxnet->peer_keepalive_work); > del_timer_sync(&rxnet->peer_keepalive_timer); > > Fix this by restoring the removed del_timer_sync() so that we try to remove > the timer twice. If the timer runs again, it should see ->live == false > and not restart the worker. > > Fixes: 1946014ca3b1 ("rxrpc: fix a race in rxrpc_exit_net()") > Signed-off-by: David Howells <dhowells@...hat.com> > cc: Eric Dumazet <edumazet@...gle.com> > cc: Marc Dionne <marc.dionne@...istor.com> > cc: linux-afs@...ts.infradead.org > Link: https://lore.kernel.org/r/20220404183439.3537837-1-eric.dumazet@gmail.com/ [1] > Link: https://syzkaller.appspot.com/bug?extid=724378c4bb58f703b09a [2] > --- > > net/rxrpc/net_ns.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/net/rxrpc/net_ns.c b/net/rxrpc/net_ns.c > index f15d6942da45..cc7e30733feb 100644 > --- a/net/rxrpc/net_ns.c > +++ b/net/rxrpc/net_ns.c > @@ -113,7 +113,9 @@ static __net_exit void rxrpc_exit_net(struct net *net) > struct rxrpc_net *rxnet = rxrpc_net(net); > > rxnet->live = false; > + del_timer_sync(&rxnet->peer_keepalive_timer); > cancel_work_sync(&rxnet->peer_keepalive_work); > + /* Remove the timer again as the worker may have restarted it. */ > del_timer_sync(&rxnet->peer_keepalive_timer); > rxrpc_destroy_all_calls(rxnet); > rxrpc_destroy_all_connections(rxnet); > > ok... so we have a timer and a work queue, both activating each other in kind of a ping pong ? Any particular reason not using delayed works ? Thanks.
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