From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-yx1-f47.google.com (mail-yx1-f47.google.com [74.125.224.47]) (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 737F7126C03 for ; Tue, 3 Mar 2026 00:33:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=74.125.224.47 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772497987; cv=none; b=s7S0FJBdZXgutoPclDIasDiNhmabE1YNM1LutKd0iPtvm4PEtppW6JM0TPHagI+wH8g873idam1qc/UPupKiO8DM0QPpS52VYiH9tE8Fy90Qk4rTlbSYrEctRDKM1ZX1FG8gNSBbmAGFkcn4XQi2xl4IrPVxr+K1CDz7vWrUgvI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772497987; c=relaxed/simple; bh=OKYgKlSTeG4GSRH5iOsE/UaIFTSGi8cSgGLLV4ZpEA8=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:To:Cc; b=stWNbCyZ5NQVz1/GnUvSwE49PDvqKG9HyLkesjLr24FtDzUt4zJK8lrasmmv9jO/ZyF4F0ZHVlimiqP+VpidzmpQgdc7Rsy3FwUHKhkdxss8zwxOLkF+QM5IlJPPj8qo7a8fYV5e/Db3gthY1o0rldvtXg3oltt6AqnGKKqU7DM= 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=eQZu/LYQ; arc=none smtp.client-ip=74.125.224.47 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="eQZu/LYQ" Received: by mail-yx1-f47.google.com with SMTP id 956f58d0204a3-649278a69c5so4366578d50.3 for ; Mon, 02 Mar 2026 16:33:05 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1772497984; x=1773102784; darn=vger.kernel.org; h=cc:to:message-id:content-transfer-encoding:mime-version:subject :date:from:from:to:cc:subject:date:message-id:reply-to; bh=8gRXaYxmpUNBUEUdJFcpug3buWfv3yzf3AEaknZ0Z1k=; b=eQZu/LYQV41Epc5ciB3Wj6JFCUIkzI/S8feSjLKd6/vYeX1fEXtgXYvPsd208hiivm 0S0FvSxggtAFmBkRrFw7zzoiGZudeyaursq3Rn6wK0EbEXffbZre1zuVYffhgPw/6d70 GcEAgVZC8GVXpwwWekFdy31UL4Vm7+OTdK3NKxkAnDlnfL1Hoc/VkSssPnr1AX8aR5O0 2KQOSn0io8sXPNu3UHLEN0vrNFmIHx/Q0OFt7Ye01S8h48JNJc/Ljihv4+7MUj2ZDGjq 9ZpSeUUyq2qjNcKCqNYMq95kSU9DioXPf1wcIms5P4lVSpFtntKGD6iF0uyJ2JHiew2x 9ong== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1772497984; x=1773102784; h=cc:to:message-id:content-transfer-encoding:mime-version:subject :date:from:x-gm-gg:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=8gRXaYxmpUNBUEUdJFcpug3buWfv3yzf3AEaknZ0Z1k=; b=k2Dfmlrx0FC1Kw8WVYEW5EdWcSJBZKLgFk/3V6pgYLyZYx98XX8DLq38QMUJ3T77bs o8ihzMZH4WkUWG9iDyhRRWqLC/1RpKSN/QhG8tN18jbu441vuHzlqIr5eJ1iCrtF4m0Q CD+e1UgUCed7aMOXQFs8pXucCDYwaV3Jtfm5yfVAvz/izRLAuYfAWjCr9CsFsNR+Qopn hWt9StZsTkS+miMu0X2NG9btFLhU81N8uOZhEGHqpmo4NNyoOsmCv3iSBcPUal5lwcQg ygOMTO0an1lMqB4sFKOzb5CnO3Jz2ufD49H8Am3TmyimTphKfG1fmN0VqjL56yrFpJpj u10A== X-Gm-Message-State: AOJu0YyvooxbFbN7BRVUSGKdRheMY3U3XL0cXIMpyigFDWx3sYHrHJT7 82B+U7ZJzYsEyoy9XfHUlU4thjhMtcU8TW1iDSFep1Hs51g/nxk3J0jf X-Gm-Gg: ATEYQzwUoloQaTXddW8Uo0UfP0TOYDf+84kWarD6RCGsjkddVQgmD0IUsEvQSRaH8ab 3nfRcWA3qGqrEKlkEVCtBaZhl8o7MdyhOiD1yGsNplASfOd2AtnQyUk3ql/OtHjRc8c+mAn73ii US5dxhQ1v0Uf3zmfoRo3nhxFNZr0TrT36dQ74QyT8r6nOc5AZ4bHdpx8QDyo9yWBNj/sit4JK44 0OatBiNtuLa2GKtH3rHiYCjryqiUcOvufS1o25ro+q5cgw9sabGyLhi5KzPyuX1LI4USil8VBlj h4nYmYUCL5eHrPl4KcFRwAMxr2/FCcgQxlDvtKkgQsEK3CqHB3K0DvZbeGZ+rM9efo7k3I6eEpT 3JeWkmRddr+MqkyIsYuIb9s230Ab5/yhAA2cA35AFoICzkVnaXTXGKn+ErhXoci3j6QF/Ds+mZT sJVHNSYllPrFgY+ZUHthNyiA== X-Received: by 2002:a05:690e:174b:b0:64c:9c10:c16 with SMTP id 956f58d0204a3-64cc2224ed0mr8535381d50.53.1772497984218; Mon, 02 Mar 2026 16:33:04 -0800 (PST) Received: from localhost ([2a03:2880:25ff:41::]) by smtp.gmail.com with ESMTPSA id 956f58d0204a3-64cb7572340sm6178927d50.1.2026.03.02.16.33.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 02 Mar 2026 16:33:03 -0800 (PST) From: Bobby Eshleman Date: Mon, 02 Mar 2026 16:32:56 -0800 Subject: [PATCH net v2] net: devmem: use READ_ONCE/WRITE_ONCE on binding->dev Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260302-devmem-membar-fix-v2-1-5b33c9cbc28b@meta.com> X-B4-Tracking: v=1; b=H4sIADgspmkC/33NQQqDMBBG4auEf+0UE1urrnqP4iJNJnUW0ZJIs Ih3L3iArh98b0fmJJwxqB2Ji2RZZgzKVApusvObSTwGBVObtjamIc8lcqTI8WUTBdmosTfn+1Z 3obOoFD6Jg2yn+cTMK8ZKYZK8Lul7foo+0x+yaNLU3L2zrPnah+4RebUXt0SMx3H8AL1y5Tq2A AAA X-Change-ID: 20260223-devmem-membar-fix-3a5cd9618f8a To: "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Mina Almasry , Kaiyuan Zhang , Stanislav Fomichev Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Bobby Eshleman X-Mailer: b4 0.14.3 From: Bobby Eshleman binding->dev is protected on the write-side in mp_dmabuf_devmem_uninstall() against concurrent writes, but due to the concurrent bare reads in net_devmem_get_binding() and validate_xmit_unreadable_skb() it should be wrapped in a READ_ONCE/WRITE_ONCE pair to make sure no compiler optimizations play with the underlying register in unforeseen ways. Doesn't present a critical bug because the known compiler optimizations don't result in bad behavior. There is no tearing on u64, and load omissions/invented loads would only break if additional binding->dev references were inlined together (they aren't right now). This just more strictly follows the linux memory model (i.e., "Lock-Protected Writes With Lockless Reads" in tools/memory-model/Documentation/access-marking.txt). Fixes: bd61848900bf ("net: devmem: Implement TX path") Signed-off-by: Bobby Eshleman --- Changes in v2: - add ASSERT_EXCLUSIVE_WRITER() to mark write-side critical section - add READ_ONCE() in validate_xmit_unreadable_skb() too - Link to v1: https://lore.kernel.org/r/20260223-devmem-membar-fix-v1-1-37dcae1e49f8@meta.com --- net/core/dev.c | 2 +- net/core/devmem.c | 6 ++++-- 2 files changed, 5 insertions(+), 3 deletions(-) diff --git a/net/core/dev.c b/net/core/dev.c index c1a9f7fdcffa..9036fcf9f965 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -3987,7 +3987,7 @@ static struct sk_buff *validate_xmit_unreadable_skb(struct sk_buff *skb, if (shinfo->nr_frags > 0) { niov = netmem_to_net_iov(skb_frag_netmem(&shinfo->frags[0])); if (net_is_devmem_iov(niov) && - net_devmem_iov_binding(niov)->dev != dev) + READ_ONCE(net_devmem_iov_binding(niov)->dev) != dev) goto out_free; } diff --git a/net/core/devmem.c b/net/core/devmem.c index 8c9aad776bf4..69d79aee07ef 100644 --- a/net/core/devmem.c +++ b/net/core/devmem.c @@ -396,7 +396,8 @@ struct net_devmem_dmabuf_binding *net_devmem_get_binding(struct sock *sk, * net_device. */ dst_dev = dst_dev_rcu(dst); - if (unlikely(!dst_dev) || unlikely(dst_dev != binding->dev)) { + if (unlikely(!dst_dev) || + unlikely(dst_dev != READ_ONCE(binding->dev))) { err = -ENODEV; goto out_unlock; } @@ -513,7 +514,8 @@ static void mp_dmabuf_devmem_uninstall(void *mp_priv, xa_erase(&binding->bound_rxqs, xa_idx); if (xa_empty(&binding->bound_rxqs)) { mutex_lock(&binding->lock); - binding->dev = NULL; + ASSERT_EXCLUSIVE_WRITER(binding->dev); + WRITE_ONCE(binding->dev, NULL); mutex_unlock(&binding->lock); } break; --- base-commit: 9439a661c2e80485406ce2c90b107ca17858382d change-id: 20260223-devmem-membar-fix-3a5cd9618f8a Best regards, -- Bobby Eshleman