From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta1.migadu.com (out-19.mta1.migadu.com [95.215.58.19]) (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 0D4834ACC8D for ; Thu, 3 Sep 2026 13:14:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.19 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788441313; cv=none; b=fIC0FynN+WB+SBWVNqfByWG1KJfnmBRzrEeFvn3A09FmGDYMbZhLhkYAWR1JZ4oZYWpgStWpjCJzdoaXq8Am1xchWcdRvHiHCYQ/OX/abK6AXaSIqo/tNP+UcuaiJ3kKBSwtUhqbsSfAdvoRKN3iE5AhSh1utc6iciRJs1Se/Vg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788441313; c=relaxed/simple; bh=2nuUgjgidPHLBNI2V9fz+MDWuBGphq9N7I7kryTPoKU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=t559JZfb+/u4ujc//RYpjbqdBBnxlAryQC8WUz8WjNeBGcHM4d91A/Auxv1exFy/DtPDMLJe6VmQD4N+TdUOOZ/fiztxZIfumVofmtWCIQnYmBnGuXOxMdOPA1EXDCrxsBgMxKbAt1LKoXXT5MJV7KXMWJRBbh/n3xYPdUap+d4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=pYPFBHUG; arc=none smtp.client-ip=95.215.58.19 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="pYPFBHUG" X-Envelope-To: mptcp@lists.linux.dev DKIM-Signature: a=rsa-sha256; bh=2nuUgjgidPHLBNI2V9fz+MDWuBGphq9N7I7kryTPoKU=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1788441274; v=1; x=1789046074; b=pYPFBHUG8E5fpQ6cLcka8N8g6vjCinCwiB4LYN7dgK7R3JJNL0S7PCpbo1mLKkh6HIqLZCbL q07KFUbwMluLpMZFRLwxk4x8EVUygMKA0Gfpmw4nYumJ3qhyrO/OdVQtzip+UNbRiFCsnPfarYZ IuLfgCJvw4wbWYSXGFR+j0Rg= X-Envelope-To: mptcp@lists.linux.dev Received: by smtp.migadu.com with ESMTPS id 6532a9406f735565; Thu, 03 Sep 2026 13:14:34 +0000 X-Mizu-Trace-ID: 6532a9406f735565 X-Migadu-Flow: FLOW_OUT From: Tao Cui To: mptcp@lists.linux.dev, matttbe@kernel.org, quanyeyang@proton.me Cc: geliang@kernel.org, cuitao@kylinos.cn, cui.tao@linux.dev Subject: [PATCH mptcp-next v2 2/3] mptcp: pm: skip extra_subflows accounting on disconnected msk Date: Thu, 3 Sep 2026 21:14:15 +0800 Message-ID: <20260903131416.1112393-3-cui.tao@linux.dev> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260903131416.1112393-1-cui.tao@linux.dev> References: <20260903131416.1112393-1-cui.tao@linux.dev> Precedence: bulk X-Mailing-List: mptcp@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Tao Cui The WARN_ON_ONCE() guards added to the extra_subflows decrement sites turn out to be reachable: mptcp_pm_data_reset() zeroes the counter with only the msk socket lock held, while an MP_JOIN subflow can still sit in msk->join_list, its reference already accounted by mptcp_pm_allow_new_subflow() under pm->lock. If the socket gets disconnected(AF_UNSPEC) in that window, mptcp_pm_data_reset() zeroes the counter, and the join list is flushed later at release_sock() time: the leftover subflow then reaches mptcp_pm_subflow_check_next() (or __mptcp_pm_close_subflow() for kernel PM sockets) with the counter already at 0, firing the warning. On panic_on_warn kernels this is a remotely triggerable panic, which is worse than the silent wrap the guards replaced. Skip the PM accounting when the msk is already in TCP_CLOSE: in the scenario above the state is set before the counters are cleared, and once the msk is closed the accounting is not relevant anymore. Keep a clamp and a rate-limited pr_warn() on the decrement sites instead, to leave a trace of any imbalance we would still not know about. Fixes: e99c1ca89071 ("mptcp: pm: add WARN_ON_ONCE guards on extra_subflows underflow") Link: https://github.com/multipath-tcp/mptcp_net-next/issues/629 Suggested-by: Matthieu Baerts Signed-off-by: Tao Cui --- net/mptcp/pm.c | 11 ++++++++++- net/mptcp/protocol.h | 14 ++++++++++++-- 2 files changed, 22 insertions(+), 3 deletions(-) diff --git a/net/mptcp/pm.c b/net/mptcp/pm.c index 07cdcdb54b15..cccf5319cce0 100644 --- a/net/mptcp/pm.c +++ b/net/mptcp/pm.c @@ -671,9 +671,18 @@ void mptcp_pm_subflow_check_next(struct mptcp_sock *msk, update_subflows = subflow->request_join || subflow->mp_join; if (mptcp_pm_is_userspace(msk)) { if (update_subflows) { + /* The PM counters have already been cleared if the + * msk got disconnected while this subflow was still + * queued in the join list + */ + if (inet_sk_state_load(sk) == TCP_CLOSE) + return; spin_lock_bh(&pm->lock); - if (!WARN_ON_ONCE(pm->extra_subflows == 0)) + if (likely(pm->extra_subflows)) pm->extra_subflows--; + else + pr_warn_ratelimited("extra_subflows underflow, msk=%p\n", + msk); spin_unlock_bh(&pm->lock); } return; diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h index 87ccb84e9927..07821551499c 100644 --- a/net/mptcp/protocol.h +++ b/net/mptcp/protocol.h @@ -1252,8 +1252,18 @@ u8 mptcp_pm_get_limit_extra_subflows(const struct mptcp_sock *msk); /* called under PM lock */ static inline void __mptcp_pm_close_subflow(struct mptcp_sock *msk) { - if (!WARN_ON_ONCE(msk->pm.extra_subflows == 0) && - --msk->pm.extra_subflows < mptcp_pm_get_limit_extra_subflows(msk)) + /* The PM counters have already been cleared if the msk got + * disconnected while this subflow was still queued in the + * join list + */ + if (inet_sk_state_load((struct sock *)msk) == TCP_CLOSE) + return; + + if (unlikely(msk->pm.extra_subflows == 0)) { + pr_warn_ratelimited("extra_subflows underflow, msk=%p\n", msk); + return; + } + if (--msk->pm.extra_subflows < mptcp_pm_get_limit_extra_subflows(msk)) WRITE_ONCE(msk->pm.accept_subflow, true); } -- 2.43.0