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=1794371216; b=2qZCekilPyLQydz4nNmWhovWD0nRuim3ETnamsi2haxTEOihkmukI2TI7HrmpMXwwUHy NFvbYGMwfUwmnRmcD45r1k2j21LLnxn8oC0uDPp+SaYd5cDHNQILv08iqR3nOSIJECRCv sm6RJBBdVVCnAAkC28zbJUHiykESZ1tnUb0XPibHnR+nTWxjYj5H0S5hYmc3DG9mSjN69 inG0nNdg7UYsTBvZINxO03JEwcsHKtxJzoft6JBPb7B6ScHL83MtPngFG4/OwUwbgAgtL sxfwpb4DYopAB+8pIIKO1cbDPXByaYjPRzZQynwMZ+ZClgOJfehq9gc/CfeKSSlf3qg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794371216; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=K6rEuhRzh71CzjoGHs6Ajg6upFo4SI6YJax4thBZYus=; b=dXFwlLHvK8gwWDP2+jBdFrcObe0e8B8fLFek91IaKrxD1Fwau8trJBw8Eye2rvYISgBw CSj6jGAoNgpFb0r0p8yRDXAzW4kZsXBGs3w/9aXPRM2IaABttBaMirTyqimxZFF/PIoyZ rZQqS0pEJvSjNrprlnb1XsUglEiRTU6Cpr32riOz07kzdxz3MC7CubUnl4PhEuePDu8We bpjFt/ygJqTM0LhBiCJ+3BmkuwaiEZkwMF/TrdoMiwKIr6kVMW3+9a18yPTweHzC8tPBb I5lm/XTbOG+1pVZI35IxHKiom8qE1KFxt70KXlhZP+KXA5Qz1/W1nz2XTPW9D8+JWEg== 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="n/qq091U"; 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 5A534606A330 for ; Wed, 11 Nov 2026 04:26:56 +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=n/qq091U Received: by smtp.kernel.org (Postfix) with ESMTPSA id 750001F0089F; Wed, 11 Nov 2026 04:26:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794371216; bh=K6rEuhRzh71CzjoGHs6Ajg6upFo4SI6YJax4thBZYus=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=n/qq091Uc6BCB/R0f4Ze6Eds5qh3tfUyCkwEiX+lOV3lOw5x66I8G26M4I1gxaSC1 Jc1VZs916nR6TUq1Y4z3yfE/rC+GNbmWymOLOCHLUEbrtRn8Y2QGpyfXKRTK/JZO/w KsjZFay6+Wmbi3/zhPYwRuVc97+tQxL9eg5SZnDIQID+YAb/zUNpw3ZufXGUc7njeu imbsmDz7A6hoPYXKBlxAnTmoDbXrCtTthWJdFixZtPieH8ILTxwgsMJ32ZS6IX1Kcs bk4B8K0CNuwCbHAp/HrHtD4ZmcyCJFH81w0mp0+Ztvy9oiHZXya4Mi0aVDLZZg9UGT RLIptIKc9Wx5w== From: Sasha Levin To: stable@vger.kernel.org Cc: Eric Dumazet , David Teigland , Alexander Aring , Kuniyuki Iwashima , Jakub Kicinski , Sasha Levin Subject: [PATCH 6.1.y] dlm: fix send buffer backpressure handling Date: Tue, 10 Nov 2026 23:26:54 -0500 Message-ID: <20261111042608.1083331-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261107054437-failed-6.1-e234d7625598@kernel.org> References: <20261107054437-failed-6.1-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 context to the older kernel_sendpage() loop with its existing ret == -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 4ad492d035dd1..6260c8ed179fd 100644 --- a/fs/dlm/lowcomms.c +++ b/fs/dlm/lowcomms.c @@ -521,10 +521,8 @@ 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); } @@ -1330,7 +1328,7 @@ static void send_to_sock(struct connection *con) trace_dlm_send(con->nodeid, ret); 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