netdev - Re: [PATCH net-next 02/13] ipv6: annotate data-races around cnf.disable

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Message-ID: <CANn89iLXrjT=JpAJNuvtqTxPC+jKto8+j62KOd5nPk25QqoOAg@mail.gmail.com>
Date: Mon, 26 Feb 2024 17:24:19 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Jiri Pirko <jiri@...nulli.us>
Cc: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, David Ahern <dsahern@...nel.org>, netdev@...r.kernel.org, 
	eric.dumazet@...il.com
Subject: Re: [PATCH net-next 02/13] ipv6: annotate data-races around cnf.disable_ipv6

On Mon, Feb 26, 2024 at 5:18 PM Jiri Pirko <jiri@...nulli.us> wrote:
>
> Mon, Feb 26, 2024 at 05:14:36PM CET, edumazet@...gle.com wrote:
> >On Mon, Feb 26, 2024 at 5:09 PM Jiri Pirko <jiri@...nulli.us> wrote:
> >>
> >> Mon, Feb 26, 2024 at 04:50:44PM CET, edumazet@...gle.com wrote:
> >> >disable_ipv6 is read locklessly, add appropriate READ_ONCE()
> >> >and WRITE_ONCE() annotations.
> >> >
> >> >Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> >> >---
> >> > net/ipv6/addrconf.c   | 12 ++++++------
> >> > net/ipv6/ip6_input.c  |  4 ++--
> >> > net/ipv6/ip6_output.c |  2 +-
> >> > 3 files changed, 9 insertions(+), 9 deletions(-)
> >> >
> >> >diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
> >> >index a280614b37652deee0d1f3c70ba1b41b01cc7d91..0d7746b113cc65303b5c2ec223b3331c3598ded6 100644
> >> >--- a/net/ipv6/addrconf.c
> >> >+++ b/net/ipv6/addrconf.c
> >> >@@ -4214,7 +4214,7 @@ static void addrconf_dad_work(struct work_struct *w)
> >> >                       if (!ipv6_generate_eui64(addr.s6_addr + 8, idev->dev) &&
> >> >                           ipv6_addr_equal(&ifp->addr, &addr)) {
> >> >                               /* DAD failed for link-local based on MAC */
> >> >-                              idev->cnf.disable_ipv6 = 1;
> >> >+                              WRITE_ONCE(idev->cnf.disable_ipv6, 1);
> >> >
> >> >                               pr_info("%s: IPv6 being disabled!\n",
> >> >                                       ifp->idev->dev->name);
> >> >@@ -6388,7 +6388,8 @@ static void addrconf_disable_change(struct net *net, __s32 newf)
> >> >               idev = __in6_dev_get(dev);
> >> >               if (idev) {
> >> >                       int changed = (!idev->cnf.disable_ipv6) ^ (!newf);
> >> >-                      idev->cnf.disable_ipv6 = newf;
> >> >+
> >> >+                      WRITE_ONCE(idev->cnf.disable_ipv6, newf);
> >> >                       if (changed)
> >> >                               dev_disable_change(idev);
> >> >               }
> >> >@@ -6397,15 +6398,14 @@ static void addrconf_disable_change(struct net *net, __s32 newf)
> >> >
> >> > static int addrconf_disable_ipv6(struct ctl_table *table, int *p, int newf)
> >> > {
> >> >-      struct net *net;
> >> >+      struct net *net = (struct net *)table->extra2;
> >>
> >> How is this related to the rest of the patch and why is it okay to
> >> access table->extra2 without holding rtnl mutex?
> >
> >table->extra2 is immutable, it can be fetched before grabbing RTNL.
> >Everything that can be done before acquiring RTNL is a win under RTNL pressure.
> >
> >I had a followup minor patch, but the patch series was already too big.
>
> I see, so this hunk should be part of that patch, not this one, I
> believe.
>

If I send a V2, I will add the followup patch instead.

IMO this is a minor point.

Thank you.