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[73.241.150.70]) by smtp.gmail.com with ESMTPSA id v1sm19402680pfg.26.2019.09.30.19.40.38 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 30 Sep 2019 19:40:38 -0700 (PDT) Subject: Re: [PATCH net] ipv6: Handle race in addrconf_dad_work To: David Ahern , Eric Dumazet , David Ahern , davem@davemloft.net, jakub.kicinski@netronome.com Cc: netdev@vger.kernel.org References: <20191001013736.25119-1-dsahern@kernel.org> <89c92628-57ec-72ec-3d05-9c4511e8ee38@gmail.com> <57eab627-8cc5-4834-a865-1970a290821a@gmail.com> From: Eric Dumazet Message-ID: <8a53dcff-729f-aaea-b136-ff997cf43e08@gmail.com> Date: Mon, 30 Sep 2019 19:40:37 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <57eab627-8cc5-4834-a865-1970a290821a@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 9/30/19 7:23 PM, David Ahern wrote: > On 9/30/19 8:01 PM, Eric Dumazet wrote: >> >> >> Do we need to keep the test on IF_READY done later in this function ? >> >> If IF_READY can disappear only under RTNL, we might clean this. >> >> (unless addrconf_dad_work() releases rtnl and reacquires it) > > Unless I am missing something none of the functions called by dad_work > release the rtnl, but your comment did have me second guessing the locking. > > The interesting cases for changing the idev flag are addrconf_notify > (NETDEV_UP and NETDEV_CHANGE) and addrconf_ifdown (reset the flag). The > former does not have the idev lock - only rtnl. The latter has both. > Checking the flag is inconsistent with respect to locks. > > As for your suggestion, the 'dead' flag is set only under rtnl in > addrconf_ifdown and it means the device is getting removed (or IPv6 is > disabled). Based on that I think the existing: > > if (idev->dead || !(idev->if_flags & IF_READY)) > goto out; > > can be moved to right after the rtnl_lock in addrconf_dad_work in place > of the above change, so the end result is: > > > diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c > index 6a576ff92c39..dd3be06d5a06 100644 > --- a/net/ipv6/addrconf.c > +++ b/net/ipv6/addrconf.c > @@ -4032,6 +4032,12 @@ static void addrconf_dad_work(struct work_struct *w) > > rtnl_lock(); > > + /* check if device was taken down before this delayed work > + * function could be canceled > + */ > + if (idev->dead || !(idev->if_flags & IF_READY)) > + goto out; > + > spin_lock_bh(&ifp->lock); > if (ifp->state == INET6_IFADDR_STATE_PREDAD) { > action = DAD_BEGIN; > @@ -4077,11 +4083,6 @@ static void addrconf_dad_work(struct work_struct *w) > goto out; > > write_lock_bh(&idev->lock); > - if (idev->dead || !(idev->if_flags & IF_READY)) { > - write_unlock_bh(&idev->lock); > - goto out; > - } > - > spin_lock(&ifp->lock); > if (ifp->state == INET6_IFADDR_STATE_DEAD) { > spin_unlock(&ifp->lock); > > > agree? > SGTM, thanks !