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=1794371531; b=oL2EXZHIA0lFuAqzVZwHwR4/HxG8IF4cGakCc1spd+m7L0t5MbVINq4eDuA0XDEeoaIC RiftRgByaTLx4YDi0MT5Od/+6QMotHpsaR+ZX6ZtlRHvQoVqckly0FVYGMWJTLRCu27Ko Gv0sy6woYRUZChCj/MT5szJdrQvedRcM0HNs6qDmwZJOFNb8TcXnN/YvrCvN8o+dbxSgw ywcfN/Jcl10V2h1WqwcVc+yZKjPkp0IpoQxmpgdgVLqjVzHSyBwB0pVzkHE8mel0TXXp+ 2fiRqx2YXa+toyfxkIKVA2YJa6Ph6YnocjQ6mfjgHBMkFA1aE9s7y95UoYOR3aTIXwg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794371531; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=PGOmZID1tJsuaCwPlZa97JVxdd2feOGBOsA+NQsqrBo=; b=guvjbltpGpHmfAkzfonzDpEJn+xNttqwhJ8rSWOLShm1cdd+ihWHoeZ2AmRCSZsgcuAp K6maxuy+WQKFM8iZZkT7sTXHihzEpcqofKUxNEWYLfy0xtUqGN5rT4AYYKP/niSefnDmg Uqevj9iFtWKbnO3cPsS3mlbiaNhbU1aLwDVT92oyJsSodiV+iVx217QiOfqWHQxugVzab Cj9ra5HSHHgeDk1rz1RxNlGThoXkC8D1YLpQ5jyycP11BMtnQ1+paeimjLdsp5NjD/8Gf 9Ab2jxH3SXeEBpt3jZt5ulWTKZcwof4S9FpnQsio7LNCQPUrA/agPCtlKCzN1WGW4rQ== 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=Vkk2POMg; 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 E84C7606A31C for ; Wed, 11 Nov 2026 04:32:10 +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=Vkk2POMg Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6F9711F0089F; Wed, 11 Nov 2026 04:32:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794371530; bh=PGOmZID1tJsuaCwPlZa97JVxdd2feOGBOsA+NQsqrBo=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=Vkk2POMgYJ8LphEfgt9L7esKivqtLWOMIv8Iv+ym7ndt5JAWAwWEaJMXFjgBTPMIo jp/PMrkdQW9NmCf1gcx/J22TibvhGSpTYmDLECOQ55lGslkutT2lzywvSvKomGNf/L Bsy9VASNKMpT399emUDM4Jwp1v6zczwlvAkdzArCIx7sTa83dKiy5SDPucgUvDDI9z Bggs94hI/OLZ+H5BL2HZyNoeVYDi2bEyOi5K2REkaKJ6T+BeKY2uy3mQqst0W8/bKM PriWNjkbdkUKF//PPpQxC8raIaxNzuQ3qOvYUCBY0NOm+Nl2zkbNneV9lb0oEi76uW Eb9tU79tUJ20A== From: Sasha Levin To: stable@vger.kernel.org Cc: Eric Dumazet , David Teigland , Alexander Aring , Kuniyuki Iwashima , Jakub Kicinski , Sasha Levin Subject: [PATCH 5.15.y] dlm: fix send buffer backpressure handling Date: Tue, 10 Nov 2026 23:32:08 -0500 Message-ID: <20261111043128.1115372-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261107060227-failed-5.15-e234d7625598@kernel.org> References: <20261107060227-failed-5.15-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: adjusted context around the existing ret == -EAGAIN guard in send_to_sock() ] 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 5b53425554077..80aae70431fea 100644 --- a/fs/dlm/lowcomms.c +++ b/fs/dlm/lowcomms.c @@ -518,10 +518,8 @@ 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: @@ -1417,7 +1415,7 @@ 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