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

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Message-ID: <ZdzAfhZgY7MuQBj0@nanopsycho>
Date: Mon, 26 Feb 2024 17:46:54 +0100
From: Jiri Pirko <jiri@...nulli.us>
To: Eric Dumazet <edumazet@...gle.com>
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

Mon, Feb 26, 2024 at 05:24:19PM CET, edumazet@...gle.com wrote:
>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.

Yeah, it is minor.

>
>Thank you.