From nobody Sun May 24 21:37:41 2026 Received: from mail-pf1-f176.google.com (mail-pf1-f176.google.com [209.85.210.176]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0F863376A0E for ; Thu, 21 May 2026 09:36:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.210.176 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779356187; cv=none; b=Iiwkl5Hkk89T7TOG+URHc+gOtrqfa6zS+xcCa7ntXfOD9c9WVO2xF7E67o8Gv+rg0lP+w96klw1SwMI3sS8DukPFepgWF/bWmmkKHH57U7LDm9FFGBmG2HiO8pjKkJoPK3vZung5RjJ8Pj3GExHetb6ugv2sYLDpNxEU3Jo65bs= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779356187; c=relaxed/simple; bh=n1Ym8sC2tYw3JwVQIr8QOYkS8HeICb8ExlRhTy/6eOY=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=MJMsrX/3riGEZoJfxzAxSJFNVd2LLVh2rV94lBaeLXaQvBUpC/iSSGLNbopcobOr5penl7BGH4P2g6pxKo7HxZ3oblktasHsHqAhUu0N1YqKcx5hHosI18OO/K/4QHpoLP435tJ3unMn0Jp+1e7rbSkdhXmMP+xPzqKt9zpMzM0= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=GvJEN88+; arc=none smtp.client-ip=209.85.210.176 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="GvJEN88+" Received: by mail-pf1-f176.google.com with SMTP id d2e1a72fcca58-824c9da9928so2475043b3a.3 for ; Thu, 21 May 2026 02:36:24 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1779356184; x=1779960984; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=7/4CELazT4J7bYabOPvJV6gl1L91iH5vUTjK50awgg4=; b=GvJEN88+9TzWf6xmEK3r7A2P3yB32DIMyFYHlyUOkwzDVeF4WXsVodMrELXe4CzbWT rjmGX3wH4XP016TSrK4mB/3pm57wiHjUk+jVJYkDeN4DRnBh5N9g/OQ85AAW4LaCJPHm tUNV37QxWodw44vyJqJLxtN6BGhNx1gE0aLuAr4hrnb1dAzVX+k9U6Sa2ARGKHsN9dZK er6jk9npkJz1vep/0HdlyoVFHuJcHYLkQz4AvY4n+xbaOaNg2BVRaV7lqEZlGKori6+b Bl/4ngO+3CSfqFdot096C/RbSGh8Kl+07KJ0edN4ab5k2KstVKBm8AXwAcVf7FzMsQn+ 6qSg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1779356184; x=1779960984; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-gg:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=7/4CELazT4J7bYabOPvJV6gl1L91iH5vUTjK50awgg4=; b=GDfqvn980dfpH+TwlRMD/8kaJQw6s2+mXpYinTreLF0xgm/SKwtSGJ9Fzh7UpQI57I RrVqA94RHsTv36EmkRljcSz/tMVyaPbhA67QxgEXVMf/cHjrDeLr7MxuNNvVb7mNGvZo U/t6S6QwyIEx0rOTj97wff+do2crIO4C62Qm5bzpYM8LkE42OO83g0y7WoxUGReWvIJh RzHH2KKG4EQybXY7DKMrV2lPQ8277rVZHhA+VinHhlunP5inLulVlM+qAgtm+kfeW6bs VeNUHjT4r6F6NAqianYULocxHypiBD262PwsEHAjn9Zczv98yK2Ney4+gKmnLjpdPPHb W9YQ== X-Forwarded-Encrypted: i=1; AFNElJ9TW7FAzDbMLgNA2cDDM7x1FTaGADVkYSvI9iFrXkU4C7LPVrB57neOoVXf3fBWEm5n03LcrZ7u6iiwZKA=@vger.kernel.org X-Gm-Message-State: AOJu0YylD+BlneNubUEXDadfmzprQiXloLUdn9wQ++0FVCjWl8gFYyKn c95eDkCpTZfcVnWzx1PVOgBv76eKik9N9TVNBSHFS0Fj77ThE+6VJBZhe6mxWU8n X-Gm-Gg: Acq92OEbxVh3Ebbw4rPsSerderFPm0Cudv1K6RiLr/U2bktU/zP2lSlg2RPLL4EKPao XH1uNzax/bypZwb9BdAVU4kYaEAexv4mZC3TdPOLMMhZBx++B35IfPT1isN3vEDkuTcVkHuTCWw lpnKhEbWr5vk4isNlWniERUhChlS4OcKZlE2Vy18iwGgaOASDLtOlrIl5/6hB1hqSpx6izbK+7t uzPG2sQiHme4w2kZX9rK7LY/vNoT8RNUwECGcIoE3efDt+7wugdO6dSVj/VyhqxokAMgrI/ilxY xPl5TIj88Iv76ah10gnU+6NTzW/HwrOUBS62i8FCiWGS5Ezw/KXj6adl0DbJodcZ7+nC118U99p +lEXqPTqyspPKPu1ZdI6GmUuGZXE5mYxUbd7FRkILds414HInxo52g6DWZ6ZzZPiJ94gJoS2wCH ypmbFVQqJguR+QMPAUEoeAX3TiIqaHlEDamLNcD0muuTxeJ+TkSyePO1IMDWDV1mSYcCQV6PQQ/ V4= X-Received: by 2002:a05:6a00:1306:b0:835:cc47:6ff8 with SMTP id d2e1a72fcca58-8414ae56cf7mr2470482b3a.45.1779356184338; Thu, 21 May 2026 02:36:24 -0700 (PDT) Received: from m-upc-A520M-HDV.flets-east.jp ([2400:2410:3f60:500:5c80:bb9e:85d5:f1b9]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-84154b1acf2sm912053b3a.22.2026.05.21.02.36.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 21 May 2026 02:36:23 -0700 (PDT) From: Yuyang Huang To: Yuyang Huang Cc: "David S. 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] ipv4: igmp: annotate data-races around im->users Date: Thu, 21 May 2026 18:36:12 +0900 Message-ID: <20260521093612.207475-1-sigefriedhyy@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" /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 --- net/ipv4/igmp.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c index 27d120183779..f2aca659b29c 100644 --- a/net/ipv4/igmp.c +++ b/net/ipv4/igmp.c @@ -1541,7 +1541,7 @@ static void ____ip_mc_inc_group(struct in_device *in_= dev, __be32 addr, } =20 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; =20 - im->users =3D 1; + WRITE_ONCE(im->users, 1); im->interface =3D in_dev; in_dev_hold(in_dev); im->multiaddr =3D addr; @@ -1784,7 +1784,10 @@ void __ip_mc_dec_group(struct in_device *in_dev, __b= e32 addr, gfp_t gfp) (i =3D rtnl_dereference(*ip)) !=3D NULL; ip =3D &i->next_rcu) { if (i->multiaddr =3D=3D addr) { - if (--i->users =3D=3D 0) { + int new_users =3D i->users - 1; + + WRITE_ONCE(i->users, new_users); + if (new_users =3D=3D 0) { ip_mc_hash_remove(in_dev, i); *ip =3D i->next_rcu; in_dev->mc_count--; @@ -2977,7 +2980,7 @@ static int igmp_mc_seq_show(struct seq_file *seq, voi= d *v) delta =3D 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); --=20 2.43.0