linux-kernel - Re: [PATCH net-next v2] net: mvpp2: Don't use dynamic allocs for local variables

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Date:   Thu, 22 Mar 2018 20:14:53 +0100
From:   Maxime Chevallier <maxime.chevallier@...tlin.com>
To:     David Miller <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        antoine.tenart@...tlin.com, thomas.petazzoni@...tlin.com,
        gregory.clement@...tlin.com, miquel.raynal@...tlin.com,
        nadavh@...vell.com, stefanc@...vell.com, ymarkman@...vell.com,
        mw@...ihalf.com
Subject: Re: [PATCH net-next v2] net: mvpp2: Don't use dynamic allocs for
 local variables

Hello David,

On Thu, 22 Mar 2018 14:47:09 -0400 (EDT),
David Miller <davem@...emloft.net> wrote :

> From: Maxime Chevallier <maxime.chevallier@...tlin.com>
> Date: Wed, 21 Mar 2018 16:14:00 +0100
> 
> > diff --git a/drivers/net/ethernet/marvell/mvpp2.c
> > b/drivers/net/ethernet/marvell/mvpp2.c index
> > 9bd35f2291d6..28e33e139178 100644 ---
> > a/drivers/net/ethernet/marvell/mvpp2.c +++
> > b/drivers/net/ethernet/marvell/mvpp2.c @@ -1913,16 +1913,11 @@
> > static void mvpp2_prs_sram_offset_set(struct mvpp2_prs_entry *pe, }
> >  
> >  /* Find parser flow entry */
> > -static struct mvpp2_prs_entry *mvpp2_prs_flow_find(struct mvpp2
> > *priv, int flow) +static int mvpp2_prs_flow_find(struct mvpp2
> > *priv, int flow) {
> > -	struct mvpp2_prs_entry *pe;
> > +	struct mvpp2_prs_entry pe;
> >  	int tid;
> >  
> > -	pe = kzalloc(sizeof(*pe), GFP_KERNEL);
> > -	if (!pe)
> > -		return NULL;
> > -	mvpp2_prs_tcam_lu_set(pe, MVPP2_PRS_LU_FLOWS);
> > -  
> 
> In order to be an equivalent change you must bzero out this 'pe'
> object on the stack.  You are only initializing the index member
> before passing it into other functions.

I agree that this is unclear, but the functions I pass these objects to
only need the index field to be set, and will fill the rest of the
object according to the underlying HW representation (these objects
mirror the HW configuration).

I can see that this is confusing, we might want to make the
mvpp2_prs_hw_read function more explicit about this.

Would comments explaning this be enough, or should I try another way to
make this cleaner ?

Thanks,

Maxime