Re: [PATCH net] bnxt_en: bring back rtnl lock in bnxt_shutdown

[Stanislav Fomichev <stfomichev@gmail.com>]

On 03/31, Breno Leitao wrote:
> Hello Stanislav,
> 
> On Fri, Mar 28, 2025 at 10:42:16AM -0700, Stanislav Fomichev wrote:
> > Taehee reports missing rtnl from bnxt_shutdown path:
> > 
> > inetdev_event (./include/linux/inetdevice.h:256 net/ipv4/devinet.c:1585)
> > notifier_call_chain (kernel/notifier.c:85)
> > __dev_close_many (net/core/dev.c:1732 (discriminator 3))
> > kernel/locking/mutex.c:713 kernel/locking/mutex.c:732)
> > dev_close_many (net/core/dev.c:1786)
> > netif_close (./include/linux/list.h:124 ./include/linux/list.h:215
> > bnxt_shutdown (drivers/net/ethernet/broadcom/bnxt/bnxt.c:16707) bnxt_en
> > pci_device_shutdown (drivers/pci/pci-driver.c:511)
> > device_shutdown (drivers/base/core.c:4820)
> > kernel_restart (kernel/reboot.c:271 kernel/reboot.c:285)
> 
> I've got this issue as well.
> 
> > 
> > Bring back the rtnl lock.
> > 
> > Link: https://lore.kernel.org/netdev/CAMArcTV4P8PFsc6O2tSgzRno050DzafgqkLA2b7t=Fv_SY=brw@mail.gmail.com/
> > Fixes: 004b5008016a ("eth: bnxt: remove most dependencies on RTNL")
> > Reported-by: Taehee Yoo <ap420073@gmail.com>
> > Signed-off-by: Stanislav Fomichev <sdf@fomichev.me>
> 
> Tested-by: Breno Leitao <leitao@debian.org>
> 
> > ---
> >  drivers/net/ethernet/broadcom/bnxt/bnxt.c | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt.c b/drivers/net/ethernet/broadcom/bnxt/bnxt.c
> > index 934ba9425857..1a70605fad38 100644
> > --- a/drivers/net/ethernet/broadcom/bnxt/bnxt.c
> > +++ b/drivers/net/ethernet/broadcom/bnxt/bnxt.c
> > @@ -16698,6 +16698,7 @@ static void bnxt_shutdown(struct pci_dev *pdev)
> >  	if (!dev)
> >  		return;
> >  
> > +	rtnl_lock();
> >  	netdev_lock(dev);
> 
> can't we leverage the `struct net_device->lock` for the shutdown.
> Basically we have the lock the single device we are turning it down.
> 
> I am wondering if we really need the big RTNL lock. This is my
> understanding of what is happening:
> 
> pci_device_shutdown() is called for a single device
>  - netdev_lock(dev)
>  - netif_close(dev);
>     - dev_close_many(&single, true);
>       - __dev_close_many()
>         - ASSERT_RTNL();
> 
> Basically we ware only closing one device, and the net_device->lock
> is already held. Shouldn't it be enough?

[..]

> Can we do something like this (from my naive point of view):
> 
> 	 static void __dev_close_many(struct list_head *head)
> 	  {
> 		  struct net_device *dev;
> 
> 	-         ASSERT_RTNL();
> 		  might_sleep();
> 
> 		  list_for_each_entry(dev, head, close_list) {
> 	+	  	ASSERT_RTNL_NET(dev);
> 			...
> 		  }

- netif_close adds dev->close_list to the list (if it was up)
- __dev_close_many walks over that list, so your new assert should
  trigger as well

But also in general, it would be nice to keep existing
rtnl+instance_lock scheme for now (except were we want to explicitly opt
out, as in queue apis); we can follow up later to un-rtnl the rest.