netdev - Re: [PATCH net-next 02/15] net: dsa: sja1105: Remove usage of iterator for list

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Date:   Sun, 10 Apr 2022 14:05:08 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Jakob Koschel <jakobkoschel@...il.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Lars Povlsen <lars.povlsen@...rochip.com>,
        Steen Hegelund <Steen.Hegelund@...rochip.com>,
        UNGLinuxDriver@...rochip.com, Ariel Elior <aelior@...vell.com>,
        Manish Chopra <manishc@...vell.com>,
        Edward Cree <ecree.xilinx@...il.com>,
        Martin Habets <habetsm.xilinx@...il.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Jiri Pirko <jiri@...nulli.us>,
        Casper Andersson <casper.casan@...il.com>,
        Bjarni Jonasson <bjarni.jonasson@...rochip.com>,
        Colin Ian King <colin.king@...el.com>,
        Michael Walle <michael@...le.cc>,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        Arnd Bergmann <arnd@...db.de>,
        Eric Dumazet <edumazet@...gle.com>,
        Di Zhu <zhudi21@...wei.com>, Xu Wang <vulab@...as.ac.cn>,
        Netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Mike Rapoport <rppt@...nel.org>,
        Brian Johannesmeyer <bjohannesmeyer@...il.com>,
        Cristiano Giuffrida <c.giuffrida@...nl>,
        "Bos, H.J." <h.j.bos@...nl>
Subject: Re: [PATCH net-next 02/15] net: dsa: sja1105: Remove usage of
 iterator for list_add() after loop

On Sun, Apr 10, 2022 at 12:51:56PM +0200, Jakob Koschel wrote:
> I've just looked at this again in a bit more detail while integrating it into the patch series.
> 
> I realized that this just shifts the 'problem' to using the 'pos' iterator variable after the loop.
> If the scope of the list iterator would be lowered to the list traversal loop it would also make sense
> to also do it for list_for_each().

Yes, but list_for_each() was never formulated as being problematic in
the same way as list_for_each_entry(), was it? I guess I'm starting to
not understand what is the true purpose of the changes.

> What do you think about doing it this way:
> 
> diff --git a/drivers/net/dsa/sja1105/sja1105_vl.c b/drivers/net/dsa/sja1105/sja1105_vl.c
> index b7e95d60a6e4..f5b0502c1098 100644
> --- a/drivers/net/dsa/sja1105/sja1105_vl.c
> +++ b/drivers/net/dsa/sja1105/sja1105_vl.c
> @@ -28,6 +28,7 @@ static int sja1105_insert_gate_entry(struct sja1105_gating_config *gating_cfg,
>                 list_add(&e->list, &gating_cfg->entries);
>         } else {
>                 struct sja1105_gate_entry *p;
> +               struct list_head *pos = NULL;
> 
>                 list_for_each_entry(p, &gating_cfg->entries, list) {
>                         if (p->interval == e->interval) {
> @@ -37,10 +38,14 @@ static int sja1105_insert_gate_entry(struct sja1105_gating_config *gating_cfg,
>                                 goto err;
>                         }
> 
> -                       if (e->interval < p->interval)
> +                       if (e->interval < p->interval) {
> +                               pos = &p->list;
>                                 break;
> +                       }
>                 }
> -               list_add(&e->list, p->list.prev);
> +               if (!pos)
> +                       pos = &gating_cfg->entries;
> +               list_add(&e->list, pos->prev);
>         }
> 
>         gating_cfg->num_entries++;
> --
> 
> > 
> > Thanks for the suggestion.
> > 
> >> 	}
> >> 
> >> 	gating_cfg->num_entries++;
> >> -----------------------------[ cut here ]-----------------------------
> > 
> > [1] https://lore.kernel.org/linux-kernel/20220407102900.3086255-12-jakobkoschel@gmail.com/
> > 
> > 	Jakob
> 
> Thanks,
> Jakob