On Mon, Nov 08, 2010 at 12:32:00PM -0800, Mike Waychison wrote: > The netconsole driver currently deadlocks if a NETDEV_UNREGISTER event > is received while netconsole is in use, which in turn causes it to pin a > reference to the network device. The first deadlock was dealt with in > 3b410a31 so that we wouldn't recursively grab RTNL, but even calling > __netpoll_cleanup isn't safe to do considering that we are in atomic > context. __netpoll_cleanup assumes it can sleep and has several > sleeping calls, such as synchronize_rcu_bh and > cancel_rearming_delayed_work. > > Fix this by deferring netpoll_cleanup using scheduling work that > operates in process context. We have to grab a reference to the > config_item in this case as we need to pin the item in place until it is > operated on. > > Signed-off-by: Mike Waychison <[email protected]> > --- > drivers/net/netconsole.c | 55 > ++++++++++++++++++++++++++++++++++++++++------ > 1 files changed, 48 insertions(+), 7 deletions(-) > > diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c > index 288a025..02ba5c4 100644 > --- a/drivers/net/netconsole.c > +++ b/drivers/net/netconsole.c > @@ -106,6 +106,7 @@ struct netconsole_target { > #endif > int np_state; > struct netpoll np; > + struct work_struct cleanup_work; > }; > > #ifdef CONFIG_NETCONSOLE_DYNAMIC > @@ -166,6 +167,22 @@ static void netconsole_target_put(struct > netconsole_target *nt) > > #endif /* CONFIG_NETCONSOLE_DYNAMIC */ > > +static void deferred_netpoll_cleanup(struct work_struct *work) > +{ > + struct netconsole_target *nt; > + unsigned long flags; > + > + nt = container_of(work, struct netconsole_target, cleanup_work); > + netpoll_cleanup(&nt->np); > + > + spin_lock_irqsave(&target_list_lock, flags); > + BUG_ON(nt->np_state != NETPOLL_CLEANING); > + nt->np_state = NETPOLL_DISABLED; > + spin_unlock_irqrestore(&target_list_lock, flags); > + > + netconsole_target_put(nt); > +} > + Where is the synchronization on the new work queue when the module is getting removed? The target get/put code does nothing to the module refcount, and cleanup_netconsole just deletes targets, it doesn't block or fail on netconsole refcounts, so you could run this work after the module has been removed and oops the system.
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