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ipv4: igmp: annotate data-races around im->users

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/proc/net/igmp walks IPv4 multicast memberships under RCU and
prints im->users without holding RTNL, while multicast join and leave
paths update the field while holding RTNL. Annotate this intentional
lockless snapshot with READ_ONCE() and the matching writers with
WRITE_ONCE().

Signed-off-by: Yuyang Huang <sigefriedhyy@gmail.com>
Reviewed-by: Jiayuan Chen <jiayuan.chen@linux.dev>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://patch.msgid.link/20260522093906.39764-1-sigefriedhyy@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Yuyang Huang 2026-05-22 18:39:06 +09:00 committed by Jakub Kicinski
parent c0aa5f1382
commit 061c0aa740
1 changed files with 7 additions and 4 deletions
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11
net/ipv4/igmp.c
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@ -1541,7 +1541,7 @@ static void ____ip_mc_inc_group(struct in_device *in_dev, __be32 addr,
}
if (im) {
im->users++;
WRITE_ONCE(im->users, im->users + 1);
ip_mc_add_src(in_dev, &addr, mode, 0, NULL, 0);
goto out;
}
@ -1550,7 +1550,7 @@ static void ____ip_mc_inc_group(struct in_device *in_dev, __be32 addr,
if (!im)
goto out;
im->users = 1;
WRITE_ONCE(im->users, 1);
im->interface = in_dev;
in_dev_hold(in_dev);
im->multiaddr = addr;
@ -1784,7 +1784,10 @@ void __ip_mc_dec_group(struct in_device *in_dev, __be32 addr, gfp_t gfp)
(i = rtnl_dereference(*ip)) != NULL;
ip = &i->next_rcu) {
if (i->multiaddr == addr) {
if (--i->users == 0) {
int new_users = i->users - 1;
WRITE_ONCE(i->users, new_users);
if (new_users == 0) {
ip_mc_hash_remove(in_dev, i);
*ip = i->next_rcu;
in_dev->mc_count--;
@ -2977,7 +2980,7 @@ static int igmp_mc_seq_show(struct seq_file *seq, void *v)
delta = im->timer.expires - jiffies;
seq_printf(seq,
"\t\t\t\t%08X %5d %d:%08lX\t\t%d\n",
im->multiaddr, im->users,
im->multiaddr, READ_ONCE(im->users),
im->tm_running,
im->tm_running ? jiffies_delta_to_clock_t(delta) : 0,
im->reporter);