From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-qk1-f199.google.com (mail-qk1-f199.google.com [209.85.222.199]) (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 0F04E51C04D for ; Fri, 18 Sep 2026 17:34:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.222.199 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789752879; cv=none; b=HF4EwhNbNb6Gf9sWFnVv5EInAFiR/kns9IICTUK4T7Da3CmKf/fjzmmQ0yUm30s3/u2LMPRlmymEn2PDnOZis7t8ardykCN9rYx+k2laHWobPAZ/1Uhm9lU3Ih/fHqeGmP78qxCFsZfHBmIBLN5m1wH5+g9SLRYtgtv5OeubA/Q= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789752879; c=relaxed/simple; bh=0/XPLyNXFdmG/2rLT7tRv7BIlIWTa5xqE/HKbfeGTlw=; h=Date:Mime-Version:Message-ID:Subject:From:To:Cc:Content-Type; b=kbLzbcdH3KTem5t43N1WthQOHqRDFNPmHUzwOYAcyYMtEv46/PkN7naKca1oj8w1quUEbeZixI004Y9tlQZjE7QcRvxW4ZGO+bL9yxf2+yP1JgI7QIAY4dChuM39qhQTzPT58U9UVIEqVPoi8DOaQcwW806rimGaO9JlgkoLoZk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--namangulati.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=SMCDCopD; arc=none smtp.client-ip=209.85.222.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--namangulati.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="SMCDCopD" Received: by mail-qk1-f199.google.com with SMTP id af79cd13be357-93a1b824e84so198761385a.2 for ; Fri, 18 Sep 2026 10:34:31 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1789752868; x=1790357668; darn=vger.kernel.org; h=content-type:cc:to:from:subject:message-id:mime-version:date:from :to:cc:subject:date:message-id:reply-to:content-type; bh=C6AEc4cXydGQr/Exrh5t746/leuXeKYVLsE6wKQpIs4=; b=SMCDCopDTtHput4Zhi2tNQBr0wIcHetsRp48qWRHEgU5zmf2iPj+9EhZcxakNqjMml 1d3w4hTyI+MHAn7otG9wOab92nBdiBNu0pw3URAA5ZZL7flXLyJseOIXGBnxkC49lQp3 qmxkSWfJJkRN2lG3PEcnrzryJ7SmwjwTjdrCqPPCFSkp/DtYoFZ2C/I8Iw/XGCnLPhFo +QTs6eKXE/Su0BPVCEDRJiF5XGMInpI+gk1MifpraNn+E/wGSyvUdvb3YBtoQ2bGSL6P jo1MZ1dNrkzPvneTm5VXWfWdHlXeO9+W81z99m4shjNc2NH12ATnEllbbOiY+cSl+eFh 2Xjw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1789752868; x=1790357668; h=content-type:cc:to:from:subject:message-id:mime-version:date :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=C6AEc4cXydGQr/Exrh5t746/leuXeKYVLsE6wKQpIs4=; b=a+BZQVpOhGMriA0oXCn2CvySlu2mwdguIeTYim/xhes7tBq3hs2Qho0MUj2KkxIXyQ +t4okZsgs3ZvvzcZFsgTlqrjIFqVudiMb6eaqK+uiKh+mF9VkPmTZatf7E16lv+4DM7p FIMzCcFYDL0FJqwo8p5fEBVVKJ70NwUW1xCXsj7GIP0EgEQ+aq6pLJIZOmNyYvUpclOx z+78chlY9gHzA7JmpyEYBOqW1lLmbNWrySGRl42zyAFk3RnnDah1RCXyEhdSH0oSBCyk vpolLABAhZiHPgEpadPOj92fwaqniVaqz6/Nz7EOpnOxxL6CFIJX5+r6VGGntL9JO7s7 Ub5g== X-Gm-Message-State: AFuF++nkYvXU3wjDtJ61DoBE1d4hvc3uknhjVsE+U55eRipV46UIfEll mDdfFqmog+MndipXxwQa7ZqdNgdJsG6T35SJCXe9E941RCBTUEDlh3lCwZmQv77desUhSq2vms6 n0Yq2AqeeNMBWwrW7kEBy+vXJwT0nS5kvqLT56WLCwwJYjZxbnIVI9URuFQDqOZy0F4bCXLbcfi fqyPkX9AEVtcxIdos/K30aih5FXJe8bOZh+c11FfH5TVJ9h1l5qt6DwptxK6DS+30= X-Received: from qknxx24.prod.google.com ([2002:a05:620a:5d98:b0:939:eccf:df56]) (user=namangulati job=prod-delivery.src-stubby-dispatcher) by 2002:a05:620a:4148:b0:93a:5d6:9ef2 with SMTP id af79cd13be357-93bdc70b23emr475000685a.36.1789752867495; Fri, 18 Sep 2026 10:34:27 -0700 (PDT) Date: Fri, 18 Sep 2026 17:34:13 +0000 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 X-Mailer: git-send-email 2.55.0.1082.g2b9226bbc0-goog Message-ID: <20260918173413.3222413-1-namangulati@google.com> Subject: [PATCH net] net: gro_cells: prevent enabling threaded NAPI on gro_cells From: Naman Gulati To: netdev@vger.kernel.org, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org Cc: bigeasy@linutronix.de, kuniyu@google.com, syzbot+f0661448aa9511ce744a@syzkaller.appspotmail.com, Naman Gulati Content-Type: text/plain; charset="UTF-8" gro_cells allocates a per-CPU struct gro_cell with per-CPU queues (cell->napi_skbs), per-CPU local_lock_t (cell->bh_lock), and per-CPU napi_struct (cell->napi). On !CONFIG_PREEMPT_RT, local_lock_t only provides lockdep annotation (and is a complete no-op when CONFIG_DEBUG_LOCK_ALLOC is disabled), relying on per-CPU locality and disabled BH context for mutual exclusion; it does not provide cross-CPU synchronization. When threaded NAPI is enabled on a device backed by gro_cells (e.g. gre0, vxlan, geneve) via sysfs or Netlink, unbound kernel threads are created for each per-CPU NAPI. When gro_cells_receive() on CPU A enqueues a packet to cell_A and calls napi_schedule(&cell_A->napi) while holding cell_A->bh_lock, the woken kthread can run concurrently on remote CPU B. When CPU B runs gro_cell_poll(&cell_A->napi) and calls __local_lock_nested_bh(&cell_A->bh_lock), lockdep detects that the lock is already held by CPU A's task and triggers a warning: WARNING: CPU: 1 PID: 377 at net/core/gro_cells.c:66 gro_cell_poll DEBUG_LOCKS_WARN_ON(l->owner) CPU: 1 UID: 0 PID: 377 Comm: napi/gre0-0 Not tainted 7.3.0-rc2 Call Trace: __local_lock_nested_bh include/linux/local_lock_internal.h:92 gro_cell_poll+0x5aa/0x6c0 net/core/gro_cells.c:66 napi_threaded_poll+0x39b/0x600 net/core/dev.c:7048 kthread+0x71e/0x870 kernel/kthread.c:464 ret_from_fork+0x5d/0x90 arch/x86/kernel/process.c:167 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:264 On !CONFIG_PREEMPT_RT kernels without lockdep, concurrent execution of __skb_queue_tail() on CPU A and __skb_dequeue() on CPU B without cross-CPU locks leads to silent queue corruption. Virtual per-CPU NAPIs cannot support unbound threaded NAPI. Just as gro_cells sets NAPI_STATE_NO_BUSY_POLL because virtual NAPIs cannot support busy polling, introduce NAPI_STATE_NO_THREADED to indicate that threaded mode is not supported. Set NAPI_STATE_NO_THREADED in gro_cells_init(), and fail early with -EOPNOTSUPP when trying to enable threaded napi on gro_cells netdevs. Fixes: 25718fdcbdd2 ("net: gro_cells: Use nested-BH locking for gro_cell") Reported-by: syzbot+f0661448aa9511ce744a@syzkaller.appspotmail.com Closes: https://lore.kernel.org/netdev/6aad6d7b.0c43d342.320d00.0001.GAE@google.com Reviewed-by: Kuniyuki Iwashima Signed-off-by: Naman Gulati --- include/linux/netdevice.h | 2 ++ net/core/gro_cells.c | 1 + net/core/net-sysfs.c | 4 +++- net/core/netdev-genl.c | 3 +++ 4 files changed, 9 insertions(+), 1 deletion(-) diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h index 87cafc932e9e..951734bc8b36 100644 --- a/include/linux/netdevice.h +++ b/include/linux/netdevice.h @@ -433,6 +433,7 @@ enum { NAPI_STATE_SCHED_THREADED, /* Napi is currently scheduled in threaded mode */ NAPI_STATE_HAS_NOTIFIER, /* Napi has an IRQ notifier */ NAPI_STATE_THREADED_BUSY_POLL, /* The threaded NAPI poller will busy poll */ + NAPI_STATE_NO_THREADED, /* Threaded mode is not supported */ }; enum { @@ -448,6 +449,7 @@ enum { NAPIF_STATE_SCHED_THREADED = BIT(NAPI_STATE_SCHED_THREADED), NAPIF_STATE_HAS_NOTIFIER = BIT(NAPI_STATE_HAS_NOTIFIER), NAPIF_STATE_THREADED_BUSY_POLL = BIT(NAPI_STATE_THREADED_BUSY_POLL), + NAPIF_STATE_NO_THREADED = BIT(NAPI_STATE_NO_THREADED), }; enum gro_result { diff --git a/net/core/gro_cells.c b/net/core/gro_cells.c index d8c0a2867120..9f8884d56f59 100644 --- a/net/core/gro_cells.c +++ b/net/core/gro_cells.c @@ -92,6 +92,7 @@ int gro_cells_init(struct gro_cells *gcells, struct net_device *dev) local_lock_init(&cell->bh_lock); set_bit(NAPI_STATE_NO_BUSY_POLL, &cell->napi.state); + set_bit(NAPI_STATE_NO_THREADED, &cell->napi.state); netif_napi_add(dev, &cell->napi, gro_cell_poll); napi_enable(&cell->napi); diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c index 352173df7578..296fdc007862 100644 --- a/net/core/net-sysfs.c +++ b/net/core/net-sysfs.c @@ -743,9 +743,11 @@ static ssize_t threaded_show(struct device *dev, static int modify_napi_threaded(struct net_device *dev, unsigned long val) { + struct napi_struct *napi; int ret; - if (list_empty(&dev->napi_list)) + napi = list_first_entry_or_null(&dev->napi_list, typeof(*napi), dev_list); + if (!napi || test_bit(NAPI_STATE_NO_THREADED, &napi->state)) return -EOPNOTSUPP; if (val != 0 && val != 1) diff --git a/net/core/netdev-genl.c b/net/core/netdev-genl.c index cb18db681640..661f87e2f015 100644 --- a/net/core/netdev-genl.c +++ b/net/core/netdev-genl.c @@ -334,6 +334,9 @@ netdev_nl_napi_set_config(struct napi_struct *napi, struct genl_info *info) if (info->attrs[NETDEV_A_NAPI_THREADED]) { int ret; + if (test_bit(NAPI_STATE_NO_THREADED, &napi->state)) + return -EOPNOTSUPP; + threaded = nla_get_uint(info->attrs[NETDEV_A_NAPI_THREADED]); ret = napi_set_threaded(napi, threaded); if (ret) -- 2.55.0.1082.g2b9226bbc0-goog