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=1794049349; b=S2pdOfHfSOXXYuqWId+dDYP7gCci+SvzPnJsgn7qgvnuBgLh2pdyz4nLh9Yoyh1k14zd bZdJPnN8wCf1bw5g9cVpj23AawUOxhoV+clVbGV3xAE28kPR82HZSEYKB6rGfb7wm3rOV sPWCHZITEADyiz+NgG9usZHknw00t1j100KwsnTowSuoSJ3F9dQccGI0Yvxve+3G+e4Iy VFY2rCamgjXK7pIhLyh5+G1Y9nQclm0rxqFuwFNzMzd/QwbiJ95CzoTi62NxSeHV99zCW lUy4byza/8s2AFYkx1oMUkM7q2PLAvsORhNwOkfFo3IvIJB+DVHDJ8QQQNOy4obqj5A== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794049349; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: MIME-Version:Content-Type:Content-Transfer-Encoding; bh=I4eONazqWFVheYYqtepRusL7d2PJZwOWbV8RYYmjYss=; b=4rCaWMIiFdBE9Ma8WXj20jAMEi5kjwjDbPIerN0sgKH7jMQGbl7wC2Ia5a6WjtSbEZKi MqmqLkIRcDvOVhyFl/0NO+KqPqUQfciI6M2gh6b5vfaGK6dBmB0NfUASOpuipM+wf3sO3 DDWE09OTeKJ9oU5Q/Y+VAMA+XF905KDrdD11YyRDkeg+2SgWnWwQ3967z724ll2zE+ypl PYCv1jb1lMAlQ24vxmvw+QmcD568KpoYKv5pZ7IsHrwTnPSIg4fjva7YF+G10685n6liX Qzi3lWr3pirsXtf3qAee5SB0hRm/1mFlHqUPEdiTq7FnPGEAxIFliOwClNak8/Xz4Hg== 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=QCbVhpge; 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 4729E606A32D for ; Sat, 7 Nov 2026 11:02:29 +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=QCbVhpge Received: by smtp.kernel.org (Postfix) with ESMTPSA id 742461F0089F; Sat, 7 Nov 2026 11:02:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794049349; bh=I4eONazqWFVheYYqtepRusL7d2PJZwOWbV8RYYmjYss=; h=From:To:Cc:Subject:Date; b=QCbVhpgeU8PKvHTwhsZbC8RrWUE/UWk+KmNO2F68aVewovnSITQaj+viUIbyAx8oJ SIEtEcAJirHd+77fEHCitNH0q6IeIiNflYWCy/qQg7qF2AICFxfpCt+tS4kcHzu9IX 7E/0KqspsxioGhso8r9rCMVsQR7BtRwu2duDvcEjVyB6pqDoTqS4j47NRt2Eg0jxLI 0RBWUSZBALXCfiIA57fwTdRKUBYHX7MmxSRWX77jYkSFpkHUdeMmr9y0fCmF4+H9Gx bBeDkZjtD5eXrSd24C5YupSCekglGcaGxy4qXEFui4MvZ/y9Z3SwqGPn/V7AfAlZli SuV7EfvDK7aQg== From: Sasha Levin To: edumazet@kernel.org, teigland@redhat.com, aahringo@redhat.com, kuniyu@google.com, kuba@kernel.org Cc: stable@vger.kernel.org Subject: FAILED: patch "[PATCH] dlm: fix send buffer backpressure handling" failed to apply to 5.15-stable tree Date: Sat, 7 Nov 2026 06:02:27 -0500 Message-ID: <20261107060227-failed-5.15-e234d7625598@kernel.org> X-Mailer: git-send-email 2.53.0 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-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The patch below does not apply to the 5.15-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y git checkout FETCH_HEAD git cherry-pick -x e234d7625598b2eaded84fa99f53c8062650828f # git commit -s git send-email --to '' --in-reply-to '20261107060227-failed-5.15-e234d7625598@kernel.org' --subject-prefix 'PATCH 5.15.y' 'HEAD^..' Thanks, Sasha ------------------ original commit in Linus's tree ------------------ >From e234d7625598b2eaded84fa99f53c8062650828f Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Tue, 29 Sep 2026 07:17:35 +0000 Subject: [PATCH] dlm: fix send buffer backpressure handling 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 --- 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 2aff1c7c17de4..abe9ae4c643fa 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. -- 2.53.0