Subject: Re: [PATCH net 1/1] ixgbe: Add locking to prevent panic when setting sriov_numvfs to zero

From: Jakub Kicinski <[email-masked]>
Date: Thu, 30 Jun 2022 08:11:34 -0700

On Thu, 30 Jun 2022 12:08:39 +0200 Piotr Skajewski wrote:
> On Tue, 28 Jun 2022 10:27:07 -0700 Jakub Kicinski wrote:
> > On Tue, 28 Jun 2022 09:53:46 -0700 Tony Nguyen wrote:  
> > > +	spin_lock_irqsave(&adapter->vfs_lock, flags);
> > > +
> > >  	/* set num VFs to 0 to prevent access to vfinfo */
> > >  	adapter->num_vfs = 0;
> > >  
> > > @@ -228,6 +231,8 @@ int ixgbe_disable_sriov(struct ixgbe_adapter *adapter)
> > >  	kfree(adapter->mv_list);
> > >  	adapter->mv_list = NULL;
> > >  
> > > +	spin_unlock_irqrestore(&adapter->vfs_lock, flags);  
> >
> > There's a pci_dev_put() in there, are you sure it won't sleep?  
> 
> Thank Jakub for your notice, during development we were aware about this
> and tests we've made on this particular case, did not report any problems
> that could be related to might_sleep in conjunction with spinlock.

To be on the safe side how about we protect adapter->num_vfs instead 
of adapter->vfinfo ?

You can hold the lock just around setting adapter->num_vfs to zero,
and then inside ixgbe_msg_task() you don't have to add the new if()
because the loop bound is already adapter->num_vfs.

Smaller change, and safer.