Subject: Re: [PATCH net-next v3] net: mana: Allow variable size indirection table

From: Simon Horman <[email-masked]>
Date: Thu, 6 Jun 2024 17:33:34 +0100

On Wed, Jun 05, 2024 at 01:39:06AM -0700, Shradha Gupta wrote:
> On Tue, Jun 04, 2024 at 10:33:49AM +0100, Simon Horman wrote:
> > On Fri, May 31, 2024 at 08:37:41AM -0700, Shradha Gupta wrote:
> > > Allow variable size indirection table allocation in MANA instead
> > > of using a constant value MANA_INDIRECT_TABLE_SIZE.
> > > The size is now derived from the MANA_QUERY_VPORT_CONFIG and the
> > > indirection table is allocated dynamically.
> > > 
> > > Signed-off-by: Shradha Gupta <[email-masked]>
> > > Reviewed-by: Dexuan Cui <[email-masked]>
> > > Reviewed-by: Haiyang Zhang <[email-masked]>
> > 
> > ...
> > 
> > > diff --git a/drivers/net/ethernet/microsoft/mana/mana_en.c b/drivers/net/ethernet/microsoft/mana/mana_en.c
> > 
> > ...
> > 
> > > @@ -2344,11 +2352,33 @@ static int mana_create_vport(struct mana_port_context *apc,
> > >  	return mana_create_txq(apc, net);
> > >  }
> > >  
> > > +static int mana_rss_table_alloc(struct mana_port_context *apc)
> > > +{
> > > +	if (!apc->indir_table_sz) {
> > > +		netdev_err(apc->ndev,
> > > +			   "Indirection table size not set for vPort %d\n",
> > > +			   apc->port_idx);
> > > +		return -EINVAL;
> > > +	}
> > > +
> > > +	apc->indir_table = kcalloc(apc->indir_table_sz, sizeof(u32), GFP_KERNEL);
> > > +	if (!apc->indir_table)
> > > +		return -ENOMEM;
> > > +
> > > +	apc->rxobj_table = kcalloc(apc->indir_table_sz, sizeof(mana_handle_t), GFP_KERNEL);
> > > +	if (!apc->rxobj_table) {
> > > +		kfree(apc->indir_table);
> > 
> > Hi, Shradha
> > 
> > Perhaps I am on the wrong track here, but I have some concerns
> > about clean-up paths.
> > 
> > Firstly.  I think that apc->indir_table should be to NULL here for
> > consistency with other clean-up paths. Or alternatively, fields of apc
> > should not set to NULL elsewhere after being freed.
> 
> Hi Simon,
> 
> Thanks for the comments. This makes sense, I am planning of consistently
> removing the NULLify from other places too as per Leon's comments.

Great!

> > In looking into this I noticed that mana_probe() does not call
> > mana_remove() or return an error in the cases where mana_probe_port()
> > or mana_attach() fail unless add_adev also fails. If so, is that
> > intentional?
> 
> Right, so most calls like mana_probe_port(), mana_attach() cleanup after
> themselves in the code if there is any error. So, not having to call
> mana_remove() in these cases in mana_probe() is intentional. But I do
> agree that an error is returned in mana_probe() only if add_adev also
> fails. I'll fix that too in the next version

I'm not entirely sure, but perhaps that is a candidate for a separate patch.

> > 
> > In any case, I would suggest as a follow-up, arranging things so that
> > when an error occurs in a function, anything that was allocated is
> > unwound before returning an error.
> > 
> > I think this would make allocation/deallocation easier to reason with.
> > And I suspect it would avoid both the need for fields of structures to
> > be zeroed after being freed, and the need to call mana_remove() from
> > mana_probe().
> 
> Agreed
> > 
> > > +		return -ENOMEM;
> > > +	}
> > > +
> > > +	return 0;
> > > +}
> > > +
> > >  static void mana_rss_table_init(struct mana_port_context *apc)
> > >  {
> > >  	int i;
> > >  
> > > -	for (i = 0; i < MANA_INDIRECT_TABLE_SIZE; i++)
> > > +	for (i = 0; i < apc->indir_table_sz; i++)
> > >  		apc->indir_table[i] =
> > >  			ethtool_rxfh_indir_default(i, apc->num_queues);
> > >  }
> > 
> > ...
> > 
> > > @@ -2739,11 +2772,17 @@ static int mana_probe_port(struct mana_context *ac, int port_idx,
> > >  	err = register_netdev(ndev);
> > >  	if (err) {
> > >  		netdev_err(ndev, "Unable to register netdev.\n");
> > > -		goto reset_apc;
> > > +		goto free_indir;
> > >  	}
> > >  
> > >  	return 0;
> > >  
> > > +free_indir:
> > > +	apc->indir_table_sz = 0;
> > > +	kfree(apc->indir_table);
> > > +	apc->indir_table = NULL;
> > > +	kfree(apc->rxobj_table);
> > > +	apc->rxobj_table = NULL;
> > >  reset_apc:
> > >  	kfree(apc->rxqs);
> > >  	apc->rxqs = NULL;
> > 
> > nit: Not strictly related to this patch, but the reset_apc code should
> >      probably be a call to mana_cleanup_port_context() as it is the dual of
> >      mana_init_port_context() which is called earlier in mana_probe_port()
> 
> Sure, let me do that too.

FWIIW, I think it would be appropriate to put that change in a separate patch.

> > 
> > ...
> > 
> > > @@ -2931,6 +2972,11 @@ void mana_remove(struct gdma_dev *gd, bool suspending)
> > >  		}
> > >  
> > >  		unregister_netdevice(ndev);
> > > +		apc->indir_table_sz = 0;
> > > +		kfree(apc->indir_table);
> > > +		apc->indir_table = NULL;
> > > +		kfree(apc->rxobj_table);
> > > +		apc->rxobj_table = NULL;
> > 
> > The code to free and zero indir_table_sz and indir_table appears twice
> > in this patch. Perhaps a helper to do this, which would be the dual
> > of mana_rss_table_alloc is in order.
> Makes sense, will change this too.

Thanks.