From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794372014; b=i8K7nHCU+Y9byPF6/NeUsAqLwTM9BVDfY2ESJOzkGfaP/jUIiGu3YnLMPhG4vGiMk5QX TkBW77hl77ampHiwByNbwVTNTF0nYUD5670mK4WKYhvCzvJwEH11edt3EqZdNEHTQc/3b 5qtifbWonO1cjNLY/GOnKjHc+h2wy2eC/XAKx5KtKyDbjMs38hMd6qK6HyfeCHbHJn35p fv1k4/jmqL9Ng4WMjW7g6KWokylyeMDWe6XjC9NyTOmj9cj/4z24HgE23G0ir0hKlt55a rViFkQmKpvxLRGrUQd4/BsstUFigfqM128fsvjeOqEDYlGXGn7s5+AM9+d6uX3BYE4A== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794372014; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=uhhjq+aM4Y2+KreFbcZr12RPwg0HucYhVWn5cZ0B7MI=; b=PISZ7Dq3wUQORuaRB2pa6jk75elJhCeFn1Bfc3ByMFAmHQYtscv5OTBlU8tsiUd+wccs PXr2jViNBZbNsXOs/do72XQnXNwOVPbq2Ni3lLfDQF4eVFig7z5WxAQVhNF1pWfd+/U+k FSnXAGYS60LHXlNOqPST+tOVGwBca2Gseqef/pxy2bWjfGzwz1ASPzaLPf8eSs8oUo44m 1zgjNNT/2IMZTMr0EX5xrTitaXM61pnlXlTtXCF8/abkKcMMxaa4NLfpZYJQ4/cHCIA0T FBxiYwCV8XGHHu0vIf2VJyloutb88HIWvLzPpTloKNAsLuCZX6KLt59SNIX6HPKRrEA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=I0f+duFq; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0787C606A321 for ; Wed, 11 Nov 2026 04:40:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=I0f+duFq Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1CE9B1F0089F; Wed, 11 Nov 2026 04:40:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794372013; bh=uhhjq+aM4Y2+KreFbcZr12RPwg0HucYhVWn5cZ0B7MI=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=I0f+duFq6FbD/e8Bvy5oDIaIseEeID8VqhmM/d83MZ05I3stxbtwXD0gC3KOGUP7k 7pOxRm8NnephuifjPH6bi4gOGHSVxBcaJDQNSmklV1EDJsNc0cHHXZoJCKFVVTH/NR rkkNKLTBiJ8KKmOc1WgCFknEiQxZBCjC0YPsh7Mpbn4sDYroDSZqYKtAcshfsdkbOm uqDP/ZaO6TZOOqL0vVgt0P0utEk5EUDMUueMxF244MxbvkqgnnWQp1FQSIFXnD9trX aIFyBFIplYb9DUE4QTJeQ2JhxRaH31FwfQFiX88GuAw5uGQv5pq7VEbxdv4VFmlE7q 2tNJDqBoxDXKw== From: Sasha Levin To: stable@vger.kernel.org Cc: Eric Dumazet , David Teigland , Alexander Aring , Kuniyuki Iwashima , Jakub Kicinski , Sasha Levin Subject: [PATCH 5.10.y] dlm: fix send buffer backpressure handling Date: Tue, 10 Nov 2026 23:40:11 -0500 Message-ID: <20261111043958.1124343-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261107061905-failed-5.10-e234d7625598@kernel.org> References: <20261107061905-failed-5.10-e234d7625598@kernel.org> X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Eric Dumazet [ Upstream commit e234d7625598b2eaded84fa99f53c8062650828f ] lowcomms.c tests and clears SOCKWQ_ASYNC_NOSPACE in con->sock->flags, but this bit has not been stored there for ten years. Commit 9cd3e072b0be ("net: rename SOCK_ASYNC_NOSPACE and SOCK_ASYNC_WAITDATA") mechanically renamed the two dlm users, then commit ceb5d58b2170 ("net: fix sock_wake_async() rcu protection") moved the bit from socket->flags to the RCU protected socket_wq->flags, where it is reachable only through sk_set_bit() and sk_clear_bit(), and is only maintained for sockets having SOCK_FASYNC set. dlm uses kernel sockets, which never have SOCK_FASYNC set, and never sets the bit itself, so the test in send_to_sock() has been false ever since. The consequence is that when sock_sendmsg() returns -EAGAIN because the socket send buffer is full, dlm no longer sets CF_APP_LIMITED, does not increment sk_write_pending, and does not return DLM_IO_END to wait for lowcomms_write_space(). It returns DLM_IO_RESCHED instead, and process_send_sockets() immediately requeues the send work. A connection to a peer that is slow to drain thus keeps cycling through sock_sendmsg() and -EAGAIN, burning CPU, instead of sleeping until TCP reports that space is available again. Test SOCK_NOSPACE instead. This is the bit that lives in socket->flags, that TCP sets whenever sendmsg() returns -EAGAIN for lack of send buffer space (tcp_sendmsg_locked() and sk_stream_wait_memory()), and that lowcomms_write_space() already clears. This restores the semantics dlm had before the bit moved. Also remove the clear_bit() of SOCKWQ_ASYNC_NOSPACE from lowcomms_write_space(), for the same reason. SCTP connections are deliberately left as they are. SCTP does not set SOCK_NOSPACE, and it never calls sk->sk_write_space(): sctp_wfree() ends up in sctp_wake_up_waiters(), which calls sctp_write_space() directly. lowcomms_write_space() is thus never invoked for an SCTP connection, and the test added here stays false, so send_to_sock() keeps returning DLM_IO_RESCHED as it does today. This is the only safe behavior, as returning DLM_IO_END would wait for a callback that never comes. Fixes: ceb5d58b2170 ("net: fix sock_wake_async() rcu protection") Cc: stable@vger.kernel.org Cc: David Teigland Acked-by: Alexander Aring Reviewed-by: Kuniyuki Iwashima Signed-off-by: Eric Dumazet Link: https://patch.msgid.link/20260929071743.23624-2-edumazet@kernel.org Signed-off-by: Jakub Kicinski [ sashal: adapted the flag check to the existing kernel_sendpage() loop while retaining its -EAGAIN guard ] Signed-off-by: Sasha Levin --- fs/dlm/lowcomms.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) diff --git a/fs/dlm/lowcomms.c b/fs/dlm/lowcomms.c index 68b765369c928..f3311621b67f7 100644 --- a/fs/dlm/lowcomms.c +++ b/fs/dlm/lowcomms.c @@ -421,10 +421,8 @@ static void lowcomms_write_space(struct sock *sk) clear_bit(SOCK_NOSPACE, &con->sock->flags); - if (test_and_clear_bit(CF_APP_LIMITED, &con->flags)) { + if (test_and_clear_bit(CF_APP_LIMITED, &con->flags)) con->sock->sk->sk_write_pending--; - clear_bit(SOCKWQ_ASYNC_NOSPACE, &con->sock->flags); - } queue_work(send_workqueue, &con->swork); out: @@ -1435,7 +1433,7 @@ static void send_to_sock(struct connection *con) msg_flags); if (ret == -EAGAIN || ret == 0) { if (ret == -EAGAIN && - test_bit(SOCKWQ_ASYNC_NOSPACE, &con->sock->flags) && + test_bit(SOCK_NOSPACE, &con->sock->flags) && !test_and_set_bit(CF_APP_LIMITED, &con->flags)) { /* Notify TCP that we're limited by the * application window size. -- 2.53.0