Re: [PATCH for-next 1/3] IB/usnic: fix deadlock

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On Fri, Dec 14, 2018 at 02:53:00AM +0000, Govindarajulu Varadarajan (gvaradar) wrote:
> On Tue, 2018-12-11 at 23:06 +0000, Jason Gunthorpe wrote:
> > On Tue, Dec 11, 2018 at 02:15:41PM -0800, Parvi Kaustubhi wrote:
> > > From: Govindarajulu Varadarajan <gvaradar@xxxxxxxxx>
> > > 
> > > There is a dead lock in usnic ib_register() and netdev_notify() path.
> > > 
> > > usnic_ib_discover_pf()
> > > > mutex_lock(&usnic_ib_ibdev_list_lock);
> > >  | usnic_ib_device_add();
> > >   | ib_register_device()
> > >    | usnic_ib_query_port()
> > >     | mutex_lock(&us_ibdev->usdev_lock);
> > >      | ib_get_eth_speed()
> > >       | rtnl_lock()
> > > 
> > > Order of locking: &usnic_ib_ibdev_list_lock -> usdev_lock -> rtnl_lock
> > > 
> > > rtnl_lock()
> > > > usnic_ib_netdevice_event()
> > >  | mutex_lock(&usnic_ib_ibdev_list_lock);
> > > 
> > > Order of locking: rtnl_lock -> &usnic_ib_ibdev_list_lock
> > > 
> > > The solution is to not handle usnic_ib_netdevice_event() with the rtnl
> > > lock held.
> > > This commit creates a single threaded workqueue to defer the handling of
> > > netdev/inet events.
> > > 
> > > Signed-off-by: Govindarajulu Varadarajan <gvaradar@xxxxxxxxx>
> > > Signed-off-by: Parvi Kaustubhi <pkaustub@xxxxxxxxx>
> > >  drivers/infiniband/hw/usnic/usnic_ib.h      |  6 +++
> > >  drivers/infiniband/hw/usnic/usnic_ib_main.c | 60 ++++++++++++++++++++++++---
> > 
> > I'm really getting sick of seeing this same code pattern in the
> > ethernet connecting drivers..  I think this is the 3rd time now I've
> > seen a fix for this same rtnl locking bug in a driver.
> 
> Is the issue here using a workqueue to handle notify?

The issue is all the code duplication..

Jason




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