From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-qk1-f198.google.com (mail-qk1-f198.google.com [209.85.222.198]) (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 2539E486421 for ; Mon, 14 Sep 2026 16:44:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.222.198 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789404245; cv=none; b=Ftb9OaIJqGiiRdEKcTkspDBrbsXV7p28Coq79XmSiVpuKcBt46sD/H13h1rwT+yrH6O9EUrDC7+QvpjXQu94hnMWZzcgoySTnIxbtBoVKb8BhJzT14Q4SKOGloy8H18Dd5ElcZUNRb/+++PfjRnsISPHxzmwP27R3/dFi3RCfIk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789404245; c=relaxed/simple; bh=B72i0TqWFDhyfs7iAPK30i8YZVrELBSfmsv2i7LPbl0=; h=Date:Mime-Version:Message-ID:Subject:From:To:Cc:Content-Type; b=dE67wBWnr9LdiLQtu+jUo7A1qKQ0/bp6YJV6wuPcXeExd+dCwusCwfmff7K+BmPUTF3ucgPGy5WJ8iUjpyltFvEMAahLulTmBX2SJqR+PcZaD49KZBZPUChUatTCJEm5RZFHTwlpLZGpw0ghnX3N7iBGD/Csxgvcp2fya22jDoY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--edumazet.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=tZWs8dX8; arc=none smtp.client-ip=209.85.222.198 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--edumazet.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="tZWs8dX8" Received: by mail-qk1-f198.google.com with SMTP id af79cd13be357-93a183a0e93so256825785a.1 for ; Mon, 14 Sep 2026 09:44:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1789404243; x=1790009043; 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=6vLuB0gCfwF6zDMyZTlgcVgD+YFlPOMK6K5wbE2DV94=; b=tZWs8dX8CXU8rIbvTxDWDcYIG+rd0snLpEROaTLOkZptnjoH0Jc+HWuCZvNDPSd2Kl 9DE0A1plI1e02htJM2twAct+nFOErTSb6nXRQvqmnurnCio4swtGc51Qtt9aXcyiHHO+ 6q3juNKxKv0IdYCgo1fUU4C0ZrCIQQ5NteGYWkigNn2vak25xccDlf/Qe+VilaUUOUy/ CGuEBh397WPSooHDtA1Q3/tKG29nKz/E6Rbf3knQlSoXdSZuIIv5O9AHabePQEpEaroo 3N/q3mqs5q7BOTfUPx1JrmAgOY1M/ky+yLAdz/BzjcBWOg8dIHtm0khRI37t0w1ydVvR QhSA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1789404243; x=1790009043; 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=6vLuB0gCfwF6zDMyZTlgcVgD+YFlPOMK6K5wbE2DV94=; b=pARUioJqiHfh7q1O2Qbq/WH5SJYh8TeHaV8csVobcYcC93XHzSCh6yJrncmc+DO80o bRGZGjD7VHVeSkMML5XrF03aLHzqE2vdY8v1KLM7epnVCwnFCyEiDJKelkzjoefywS1S v2L+49jEsLDn8IiJFdimehR83UexaFRYl601CXs6YC6A+SgJk3NouBBul1LU1+fLAWj0 JBLzlS7xlvje40d+8feIl1H/SqUUsd39qKmNBv29/cqYMbOAXjoDwtDKNNPtIwYC2sAs FYJ4uixUdUvMUHLIYtKOjaKn0b0p3CrE82+kQa11KzkN+7O510zWOdu7C5SGZkIdg34z 4v2g== X-Forwarded-Encrypted: i=1; AKwUvBybtgHr/T8+LNWdzvnyP8AyS2WLlQrSkhrf9OmNMvut0Uu6zVFDPf0rctY28iwrbe0PVSm49qE=@vger.kernel.org X-Gm-Message-State: AFuF++l1B/UrQfZbRJfuoaGKCLUsx4xDTyaCxPr/60SoslVTUqkzCQv5 q7ffB6Lp/a6DRXpi8D4Ve3fhWBYqasangvcaecTScso1ZR0xGb6jqNPORGkI9qns6Xst6v2Ir/K 7CC954dHs9aFwTg== X-Received: from qknrb22.prod.google.com ([2002:a05:620a:8d16:b0:93a:8de:9f99]) (user=edumazet job=prod-delivery.src-stubby-dispatcher) by 2002:a05:620a:4409:b0:939:9c21:8ece with SMTP id af79cd13be357-93a29a192e5mr456272385a.42.1789404242566; Mon, 14 Sep 2026 09:44:02 -0700 (PDT) Date: Mon, 14 Sep 2026 16:44:00 +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 2.55.0.1032.g73a4cd73de-goog Message-ID: <20260914164400.2738350-1-edumazet@google.com> Subject: [PATCH] dlm: fix send buffer backpressure handling From: Eric Dumazet To: Alexander Aring , David Teigland Cc: linux-kernel , gfs2@lists.linux.dev, Eric Dumazet , netdev@vger.kernel.org, Eric Dumazet , stable@vger.kernel.org Content-Type: text/plain; charset="UTF-8" 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 Signed-off-by: Eric Dumazet --- 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 2aff1c7c17de..abe9ae4c643f 100644 --- a/fs/dlm/lowcomms.c +++ b/fs/dlm/lowcomms.c @@ -522,10 +522,8 @@ static void lowcomms_write_space(struct sock *sk) clear_bit(SOCK_NOSPACE, &con->sock->flags); spin_lock_bh(&con->writequeue_lock); - 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); - } lowcomms_queue_swork(con); spin_unlock_bh(&con->writequeue_lock); @@ -1391,7 +1389,7 @@ static int send_to_sock(struct connection *con) if (ret == -EAGAIN || ret == 0) { lock_sock(con->sock->sk); spin_lock_bh(&con->writequeue_lock); - if (test_bit(SOCKWQ_ASYNC_NOSPACE, &con->sock->flags) && + if (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. -- 2.55.0.1007.g17ff1f9808-goog