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Miller" , David Ahern , Eric Dumazet , Ido Schimmel , Jakub Kicinski , Paolo Abeni , Simon Horman , linux-kernel@vger.kernel.org, netdev@vger.kernel.org Subject: [PATCH net-next v2 1/2] ipv6: mcast: annotate data-races around mca_flags Date: Tue, 9 Jun 2026 17:11:12 +0900 Message-ID: <20260609081113.7613-2-sigefriedhyy@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260609081113.7613-1-sigefriedhyy@gmail.com> References: <20260609081113.7613-1-sigefriedhyy@gmail.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit /proc/net/igmp6 walks IPv6 multicast memberships under RCU and prints mca_flags without holding idev->mc_lock. The multicast paths update the field while holding idev->mc_lock. Annotate this intentional lockless snapshot with READ_ONCE() and the matching writers with WRITE_ONCE(). Signed-off-by: Yuyang Huang --- net/ipv6/mcast.c | 52 +++++++++++++++++++++++++++++------------------- 1 file changed, 32 insertions(+), 20 deletions(-) diff --git a/net/ipv6/mcast.c b/net/ipv6/mcast.c index b8901c921c5e..bd3972730aa0 100644 --- a/net/ipv6/mcast.c +++ b/net/ipv6/mcast.c @@ -676,7 +676,7 @@ static void igmp6_group_added(struct ifmcaddr6 *mc) return; if (!(mc->mca_flags&MAF_LOADED)) { - mc->mca_flags |= MAF_LOADED; + WRITE_ONCE(mc->mca_flags, mc->mca_flags | MAF_LOADED); if (ndisc_mc_map(&mc->mca_addr, buf, dev, 0) == 0) dev_mc_add(dev, buf); } @@ -712,7 +712,7 @@ static void igmp6_group_dropped(struct ifmcaddr6 *mc) return; if (mc->mca_flags&MAF_LOADED) { - mc->mca_flags &= ~MAF_LOADED; + WRITE_ONCE(mc->mca_flags, mc->mca_flags & ~MAF_LOADED); if (ndisc_mc_map(&mc->mca_addr, buf, dev, 0) == 0) dev_mc_del(dev, buf); } @@ -886,7 +886,7 @@ static struct ifmcaddr6 *mca_alloc(struct inet6_dev *idev, if (ipv6_addr_is_ll_all_nodes(&mc->mca_addr) || IPV6_ADDR_MC_SCOPE(&mc->mca_addr) < IPV6_ADDR_SCOPE_LINKLOCAL) - mc->mca_flags |= MAF_NOREPORT; + WRITE_ONCE(mc->mca_flags, mc->mca_flags | MAF_NOREPORT); return mc; } @@ -1167,7 +1167,7 @@ static void igmp6_group_queried(struct ifmcaddr6 *ma, unsigned long resptime) if (!mod_delayed_work(mld_wq, &ma->mca_work, delay)) refcount_inc(&ma->mca_refcnt); - ma->mca_flags |= MAF_TIMER_RUNNING; + WRITE_ONCE(ma->mca_flags, ma->mca_flags | MAF_TIMER_RUNNING); } /* mark EXCLUDE-mode sources */ @@ -1195,7 +1195,7 @@ static bool mld_xmarksources(struct ifmcaddr6 *pmc, int nsrcs, } } } - pmc->mca_flags &= ~MAF_GSQUERY; + WRITE_ONCE(pmc->mca_flags, pmc->mca_flags & ~MAF_GSQUERY); if (scount == nsrcs) /* all sources excluded */ return false; return true; @@ -1227,10 +1227,10 @@ static bool mld_marksources(struct ifmcaddr6 *pmc, int nsrcs, } } if (!scount) { - pmc->mca_flags &= ~MAF_GSQUERY; + WRITE_ONCE(pmc->mca_flags, pmc->mca_flags & ~MAF_GSQUERY); return false; } - pmc->mca_flags |= MAF_GSQUERY; + WRITE_ONCE(pmc->mca_flags, pmc->mca_flags | MAF_GSQUERY); return true; } @@ -1499,18 +1499,25 @@ static void __mld_query_work(struct sk_buff *skb) } } else { for_each_mc_mclock(idev, ma) { + unsigned int flags; + if (!ipv6_addr_equal(&group, &ma->mca_addr)) continue; - if (ma->mca_flags & MAF_TIMER_RUNNING) { + flags = ma->mca_flags; + + if (flags & MAF_TIMER_RUNNING) { /* gsquery <- gsquery && mark */ if (!mark) - ma->mca_flags &= ~MAF_GSQUERY; + WRITE_ONCE(ma->mca_flags, + flags & ~MAF_GSQUERY); } else { /* gsquery <- mark */ if (mark) - ma->mca_flags |= MAF_GSQUERY; + WRITE_ONCE(ma->mca_flags, + flags | MAF_GSQUERY); else - ma->mca_flags &= ~MAF_GSQUERY; + WRITE_ONCE(ma->mca_flags, + flags & ~MAF_GSQUERY); } if (!(ma->mca_flags & MAF_GSQUERY) || mld_marksources(ma, ntohs(mlh2->mld2q_nsrcs), mlh2->mld2q_srcs)) @@ -1618,8 +1625,9 @@ static void __mld_report_work(struct sk_buff *skb) if (ipv6_addr_equal(&ma->mca_addr, &mld->mld_mca)) { if (cancel_delayed_work(&ma->mca_work)) refcount_dec(&ma->mca_refcnt); - ma->mca_flags &= ~(MAF_LAST_REPORTER | - MAF_TIMER_RUNNING); + WRITE_ONCE(ma->mca_flags, + ma->mca_flags & ~(MAF_LAST_REPORTER | + MAF_TIMER_RUNNING)); break; } } @@ -2018,8 +2026,10 @@ static struct sk_buff *add_grec(struct sk_buff *skb, struct ifmcaddr6 *pmc, if (pgr) pgr->grec_nsrcs = htons(scount); - if (isquery) - pmc->mca_flags &= ~MAF_GSQUERY; /* clear query state */ + if (isquery) { + /* clear query state */ + WRITE_ONCE(pmc->mca_flags, pmc->mca_flags & ~MAF_GSQUERY); + } return skb; } @@ -2612,7 +2622,8 @@ static void igmp6_join_group(struct ifmcaddr6 *ma) if (!mod_delayed_work(mld_wq, &ma->mca_work, delay)) refcount_inc(&ma->mca_refcnt); - ma->mca_flags |= MAF_TIMER_RUNNING | MAF_LAST_REPORTER; + WRITE_ONCE(ma->mca_flags, ma->mca_flags | + MAF_TIMER_RUNNING | MAF_LAST_REPORTER); } static int ip6_mc_leave_src(struct sock *sk, struct ipv6_mc_socklist *iml, @@ -2713,8 +2724,8 @@ static void mld_mca_work(struct work_struct *work) igmp6_send(&ma->mca_addr, ma->idev->dev, ICMPV6_MGM_REPORT); else mld_send_report(ma->idev, ma); - ma->mca_flags |= MAF_LAST_REPORTER; - ma->mca_flags &= ~MAF_TIMER_RUNNING; + WRITE_ONCE(ma->mca_flags, (ma->mca_flags | MAF_LAST_REPORTER) & + ~MAF_TIMER_RUNNING); mutex_unlock(&ma->idev->mc_lock); ma_put(ma); @@ -2972,13 +2983,14 @@ static int igmp6_mc_seq_show(struct seq_file *seq, void *v) { struct ifmcaddr6 *im = (struct ifmcaddr6 *)v; struct igmp6_mc_iter_state *state = igmp6_mc_seq_private(seq); + unsigned int mca_flags = READ_ONCE(im->mca_flags); seq_printf(seq, "%-4d %-15s %pi6 %5d %08X %ld\n", state->dev->ifindex, state->dev->name, &im->mca_addr, - READ_ONCE(im->mca_users), im->mca_flags, - (im->mca_flags & MAF_TIMER_RUNNING) ? + READ_ONCE(im->mca_users), mca_flags, + (mca_flags & MAF_TIMER_RUNNING) ? jiffies_to_clock_t(im->mca_work.timer.expires - jiffies) : 0); return 0; } -- 2.43.0