From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wr1-f46.google.com (mail-wr1-f46.google.com [209.85.221.46]) (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 1A0B8421EED for ; Thu, 30 Apr 2026 13:40:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.221.46 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777556427; cv=none; b=XoWaW1YTUwZcmmMiusCV8xLqklHjfGLBuBHFl7n/5hDuEOnb8swRnOL1byGx8kOa60fXj6BVJhfloWsg3TPnckw0qp2EyKOWoPrkuFMVe2yuKNG2zbRMIywalU47UhBC0dGvO06O8xFy5UvHj8w2hHPb8Jf5ZB20zhy+WNWNxXs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777556427; c=relaxed/simple; bh=1Q8gPJRbLKvxl+YiS05Ql7kIIA7PEhekTKGpZyGAQKE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=CXPiCg8sR1GYkrgz3uImnkDDcSyZhz7U1SizmC2yJqceBKyZkzEdfk7217cOkv/d+Y1s94jms/IJVgzq0gs6dDMIsc3e6Rc8EcvNOtRoM+RjF1M8YqTw5UKA8ckSLi7rcJXFkg4nX2udxLd0cE3a622bpdRGcDuh9WRUWXLZtZo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=openvpn.net; spf=pass smtp.mailfrom=openvpn.com; dkim=pass (2048-bit key) header.d=openvpn.net header.i=@openvpn.net header.b=IHTGmAYc; arc=none smtp.client-ip=209.85.221.46 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=openvpn.net Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=openvpn.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=openvpn.net header.i=@openvpn.net header.b="IHTGmAYc" Received: by mail-wr1-f46.google.com with SMTP id ffacd0b85a97d-43d77f60944so669732f8f.3 for ; Thu, 30 Apr 2026 06:40:24 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=openvpn.net; s=google; t=1777556423; x=1778161223; darn=vger.kernel.org; h=content-transfer-encoding:in-reply-to:organization:autocrypt:from :content-language:references:cc:to:subject:user-agent:mime-version :date:message-id:from:to:cc:subject:date:message-id:reply-to; bh=OgprZokyNVIp4p2Q3DRIko6UaG2F5eG39GafL3lERmg=; b=IHTGmAYcByXcBuj2fJ0IFnbZVhHirokfjOdt6LHHov02r4ShS4N0Jjfjwvu6RgWKvc VqD4oGp1cILdDrCf4meq7Kh3JO4qrbUOPigOzBFHjCmhDIpApMpf5hJfgctaS8nyMqYh Gku6RMautUOlN5oaJvg0BCVhHBsaA8joT7kW5V6KzADee8yith5bZGcOH0KYvRdphiZA iFjt9nlwezmHyHkJOTEOCJnmtlGqtOd2kgnJncOxTYdEhc+0dB+AlFFck9mtbawfX5WL Y5iqjs29n1gXe6BApGXPzOIQY61kddNaP/rFNdSmBApCjqT3ovOx6Elw9zZjNfW1/rKW msYA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1777556423; x=1778161223; h=content-transfer-encoding:in-reply-to:organization:autocrypt:from :content-language:references:cc:to:subject:user-agent:mime-version :date:message-id:x-gm-gg:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=OgprZokyNVIp4p2Q3DRIko6UaG2F5eG39GafL3lERmg=; b=CaymgZyVNSvWxPTRNx6/jxMdyKNboZqyyW/KE48SXsjQSQsHXbzxTSZ8z/EdjH53C5 jxV18kO1YafWPiO/i/94+cihN2PXte2ItTCA9AyLxnJVXtKq2p+KMipWcYq5YgM9g20y 2CdYzhuAlz83DQAMdpqUQcNOLeIw2Arj6sQzN1/kXiOWnwc3LBoTvPZ7OOySSN+zWuVE kwm+zPJ+7SvGq14bSpRJHHnFML/ogJqiv0EL3t4hR2MLCCYiAUi8fBdk9OixW8lD2Evg U0e69NDGk65Hvn3WNd7pLsOz3sTVLid/6KMzZH6UAdbol6PTGTO3wJj+KE5NsGp+OzkV zqtw== X-Gm-Message-State: AOJu0YxLNPOarTyeFZinUmAO5NZJGTL+UovHa/TQGi28+XlLq1tiVkM4 E9/1cxRlXMh86ky9pVT12vKdnHqReibDr0kUfdHzRlmmtzu1gH7tHlGtiTJdHAyNKb7073rppZu OLUfopCmK10IUabM1Gg2BRy9waMhms/YzvaGcEzgThpCWUZL1eh8= X-Gm-Gg: AeBDiesrAO5SAcapKminrwyorvpNnjWnRFREI2iLvJvt8JY3chKspPXUs2Z6R1ii39W C4xDlsV7RxIO7fBUtZFDJSR5PsRoURGPvlfxFBXsYAuNA9IVs/qROcJaCcgW/hm1TbpnT0wtbtV JAcKfh3pay36SBjRzic3NXqlOwIRyqKGNMmvl54UzqtPzliMLmgcFqY7lc+387KTL1JbNSXGYxj wcSdl/vSx15DK1nzFsIMExx/lXD6EtUl3PTr8VjfC4S1kXh5Xhr03qaNQsKXifBACHOL6i9ABrs QsvP8u/KfoFvGqQi8adwVQxzIVhbc6+GCQOmKyrhzcxNzBm3WYS/Y4Y4cf7fErHiWrguHwTG/ml TzEBQugfckCsiZCo3eu8TwPIRStk/IT9rRTnvdi7OBg2aBnAhAqQWmXUxJ9JsAcU1aDa61f76Bc fyIxDgtxBtnhgsuvzoJIBI7hUodGBIpKJh8WXFKyB2JwyhIPrD8aUB7wSnvI+oJTMzLhF7RZKs X-Received: by 2002:a05:6000:288b:b0:43d:7af0:3a7c with SMTP id ffacd0b85a97d-4493ec61dcdmr5201830f8f.29.1777556423074; Thu, 30 Apr 2026 06:40:23 -0700 (PDT) Received: from ?IPV6:2001:67c:2fbc:1:2493:6197:23ff:7e65? ([2001:67c:2fbc:1:2493:6197:23ff:7e65]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-447b7217a57sm12616174f8f.24.2026.04.30.06.40.22 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 30 Apr 2026 06:40:22 -0700 (PDT) Message-ID: <4930aa65-6d0e-4ff8-8e7b-91feee1ce646@openvpn.net> Date: Thu, 30 Apr 2026 15:40:21 +0200 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net 2/2] ovpn: ensure gro_cells_receive() is invoked with BH disabled To: Eric Dumazet Cc: netdev@vger.kernel.org, Jakub Kicinski , ralf@mandelbit.com, Sabrina Dubroca , Paolo Abeni , Andrew Lunn , "David S. Miller" References: <20260429120120.514491-1-antonio@openvpn.net> <20260429120120.514491-3-antonio@openvpn.net> <5b281966-c278-46d5-ade0-9dc24175de6e@openvpn.net> Content-Language: en-US From: Antonio Quartulli Autocrypt: addr=antonio@openvpn.net; keydata= xsFNBFN3k+ABEADEvXdJZVUfqxGOKByfkExNpKzFzAwHYjhOb3MTlzSLlVKLRIHxe/Etj13I X6tcViNYiIiJxmeHAH7FUj/yAISW56lynAEt7OdkGpZf3HGXRQz1Xi0PWuUINa4QW+ipaKmv voR4b1wZQ9cZ787KLmu10VF1duHW/IewDx9GUQIzChqQVI3lSHRCo90Z/NQ75ZL/rbR3UHB+ EWLIh8Lz1cdE47VaVyX6f0yr3Itx0ZuyIWPrctlHwV5bUdA4JnyY3QvJh4yJPYh9I69HZWsj qplU2WxEfM6+OlaM9iKOUhVxjpkFXheD57EGdVkuG0YhizVF4p9MKGB42D70pfS3EiYdTaKf WzbiFUunOHLJ4hyAi75d4ugxU02DsUjw/0t0kfHtj2V0x1169Hp/NTW1jkqgPWtIsjn+dkde dG9mXk5QrvbpihgpcmNbtloSdkRZ02lsxkUzpG8U64X8WK6LuRz7BZ7p5t/WzaR/hCdOiQCG RNup2UTNDrZpWxpwadXMnJsyJcVX4BAKaWGsm5IQyXXBUdguHVa7To/JIBlhjlKackKWoBnI Ojl8VQhVLcD551iJ61w4aQH6bHxdTjz65MT2OrW/mFZbtIwWSeif6axrYpVCyERIDEKrX5AV rOmGEaUGsCd16FueoaM2Hf96BH3SI3/q2w+g058RedLOZVZtyQARAQABzSdBbnRvbmlvIFF1 YXJ0dWxsaSA8YW50b25pb0BvcGVudnBuLm5ldD7Cwa0EEwEIAFcCGwMFCwkIBwMFFQoJCAsF FgIDAQACHgECF4AYGGhrcHM6Ly9rZXlzLm9wZW5wZ3Aub3JnFiEEyr2hKCAXwmchmIXHSPDM to9Z0UwFAmj3PEoFCShLq0sACgkQSPDMto9Z0Uw7/BAAtMIP/wzpiYn+Di0TWwNAEqDUcGnv JQ0CrFu8WzdtNo1TvEh5oqSLyO0xWaiGeDcC5bQOAAumN+0Aa8NPqhCH5O0eKslzP69cz247 4Yfx/lpNejqDaeu0Gh3kybbT84M+yFJWwbjeT9zPwfSDyoyDfBHbSb46FGoTqXR+YBp9t/CV MuXryL/vn+RmH/R8+s1T/wF2cXpQr3uXuV3e0ccKw33CugxQJsS4pqbaCmYKilLmwNBSHNrD 77BnGkml15Hd6XFFvbmxIAJVnH9ZceLln1DpjVvg5pg4BRPeWiZwf5/7UwOw+tksSIoNllUH 4z/VgsIcRw/5QyjVpUQLPY5kdr57ywieSh0agJ160fP8s/okUqqn6UQV5fE8/HBIloIbf7yW LDE5mYqmcxDzTUqdstKZzIi91QRVLgXgoi7WOeLF2WjITCWd1YcrmX/SEPnOWkK0oNr5ykb0 4XuLLzK9l9MzFkwTOwOWiQNFcxXZ9CdW2sC7G+uxhQ+x8AQW+WoLkKJF2vbREMjLqctPU1A4 557A9xZBI2xg0xWVaaOWr4eyd4vpfKY3VFlxLT7zMy/IKtsm6N01ekXwui1Zb9oWtsP3OaRx gZ5bmW8qwhk5XnNgbSfjehOO7EphsyCBgKkQZtjFyQqQZaDdQ+GTo1t6xnfBB6/TwS7pNpf2 ZvLulFbOOARoRsrsEgorBgEEAZdVAQUBAQdAyD3gsxqcxX256G9lLJ+NFhi7BQpchUat6mSA Pb+1yCQDAQgHwsF8BBgBCAAmFiEEyr2hKCAXwmchmIXHSPDMto9Z0UwFAmhGyuwCGwwFCQHh M4AACgkQSPDMto9Z0UwymQ//Z1tIZaaJM7CH8npDlnbzrI938cE0Ry5acrw2EWd0aGGUaW+L +lu6N1kTOVZiU6rnkjib+9FXwW1LhAUiLYYn2OlVpVT1kBSniR00L3oE62UpFgZbD3hr5S/i o4+ZB8fffAfD6llKxbRWNED9UrfiVh02EgYYS2Jmy+V4BT8+KJGyxNFv0LFSJjwb8zQZ5vVZ 5FPYsSQ5JQdAzYNmA99cbLlNpyHbzbHr2bXr4t8b/ri04Swn+Kzpo+811W/rkq/mI1v+yM/6 o7+0586l1MQ9m0LMj6vLXrBDN0ioGa1/97GhP8LtLE4Hlh+S8jPSDn+8BkSB4+4IpijQKtrA qVTaiP4v3Y6faqJArPch5FHKgu+rn7bMqoipKjVzKGUXroGoUHwjzeaOnnnwYMvkDIwHiAW6 XgzE5ZREn2ffEsSnVPzA4QkjP+QX/5RZoH1983gb7eOXbP/KQhiH6SO1UBAmgPKSKQGRAYYt cJX1bHWYQHTtefBGoKrbkzksL5ZvTdNRcC44/Z5u4yhNmAsq4K6wDQu0JbADv69J56jPaCM+ gg9NWuSR3XNVOui/0JRVx4qd3SnsnwsuF5xy+fD0ocYBLuksVmHa4FsJq9113Or2fM+10t1m yBIZwIDEBLu9zxGUYLenla/gHde+UnSs+mycN0sya9ahOBTG/57k7w/aQLc= Organization: OpenVPN Inc. In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Hi Eric, On 30/04/2026 15:37, Eric Dumazet wrote: > On Thu, Apr 30, 2026 at 6:28 AM Antonio Quartulli wrote: >> >> Hi Jakub, >> >> sashiko came back with an interesting review of the per-cpu stats update >> in the surrounding code. >> >> As far as I can tell its explanation makes sense, but I am no per-cpu >> expert. >> >> IIUC it basically says that if gro_cells_receive() is invoked with >> bottom halves disabled, the following dev_dstats_rx_add() should be too >> to avoid deadlocks and corruptions. >> >> See below: >> >> On 29/04/2026 14:01, Antonio Quartulli wrote: >>> diff --git a/drivers/net/ovpn/io.c b/drivers/net/ovpn/io.c >>> index d92bb87be2b2..c0fdb9504241 100644 >>> --- a/drivers/net/ovpn/io.c >>> +++ b/drivers/net/ovpn/io.c >>> @@ -91,7 +91,13 @@ static void ovpn_netdev_write(struct ovpn_peer *peer, struct sk_buff *skb) >>> >>> /* cause packet to be "received" by the interface */ >>> pkt_len = skb->len; >>> + /* we may get here in process context in case of TCP connections, >>> + * therefore we have to disable BHs to ensure gro_cells_receive() >>> + * doesn't enter deadlock >>> + */ >>> + local_bh_disable(); >>> ret = gro_cells_receive(&peer->ovpn->gro_cells, skb); >>> + local_bh_enable(); >>> if (likely(ret == NET_RX_SUCCESS)) { >>> /* update RX stats with the size of decrypted packet */ >>> ovpn_peer_stats_increment_rx(&peer->vpn_stats, pkt_len); >> >> dev_dstats_rx_add(peer->ovpn->dev...) << not visible in the diff, >> but it's here >> >> from sashiko: >> >> Can this lead to seqcount deadlocks and stat corruption since >> dev_dstats_rx_add() is executed with preemption and bottom-halves enabled? >> dev_dstats_rx_add() operates on per-CPU statistics and protects 64-bit >> updates with a sequence counter (u64_stats_update_begin()). When called >> from process context with BH enabled, on 64-bit systems, this_cpu_ptr() >> is evaluated with preemption enabled. If the task is migrated mid-update, >> it risks cross-CPU stat corruption. >> On 32-bit systems, u64_stats_update_begin() disables preemption but not >> bottom-halves. If a softirq (e.g., a concurrent UDP packet reception) >> interrupts the process context and calls dev_dstats_rx_add() for the same >> interface, it will re-enter the seqcount writer lock on the exact same CPU. >> This corrupts the sequence counter, causing readers to see an unlocked >> sequence during active writes, leading to torn reads and corrupted stats. >> Should local_bh_enable() be moved after the statistics updates to ensure >> the entire per-CPU update is atomic with respect to softirqs? >> >> >> Do you have an opinion? > > Sashiko suggestion seems good to me. But am I right saying that this bug existed before and it is not introduced by this patch? A concurrent softirq (UDP RX pkt) could already trigger this problem before we introduced the local_bh_disable/enable() calls, right? Regards, > > Proper Fixes: tag would be: > > Fixes: ab66abbc769b ("ovpn: implement basic RX path (UDP)") -- Antonio Quartulli OpenVPN Inc.