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=1794048280; b=IxgYNaVXza9FjXX5X691Udqrb/LsJtotYbEbQ/Z3c40VjPFo7UUy1cAOkV0XXtFaaQ3R DsD5qu15/E0tlTKBeiazEWcnwQFKPB07QPccNOCIqYo/BP+kutuL8TdldBxSRGma1Ost+ E/Fv4PxHihTmBLXMZIJQIQ+6kOdlsdNTPef5q+xIbTpznTwj6PZaG3+Yff7sfzs/V78YI fwD6AvWQlhwkeO5v9RarpJlWJdrZfeJU1Kk3nvCxZifXGaRAprGN+J93TAd9Ee8090UNx ukp1aNHPf1RIfebenniKqCxLRRoIK27JNgv7iyhBmKuXaa2vMUSgI2R/HyjysG6JrpQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794048280; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: MIME-Version:Content-Type:Content-Transfer-Encoding; bh=pElnO3z2wuOHoD7Ln3dqX3KX5P995BBlt3Vhhft2FlE=; b=kGw+JXQcPYH427RRARlE1q/xtrRZqJt5bm1dqDU9oPDlCjDAM9quem8JIBXgbRsk3qLj iWX4q10DkOwyuq6ncc7cAXqj6tJD56h6u5cTpmeYk8FxduVoOqSlsc/zlbop5LOLmyXG9 4vz6yQzLDrsp4HkSjv6ivy/GFCyMAwY19dBsMOq/bjTmR7QNHRSpbzeBjWbaoH64S9jXg slB+YR9EmZgvsrcVn5qS0XQHJfGkh2xzBk4cIpVuQNSLDA5q/76UEM3bWl2nsW2FK8g5y NcjDyhduWmp8f4cuYMctKPkG5nWnVbZkgaI3fa0/nRWV/rczO4uq8vnO8X+ulf8P+iQ== 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=VVN5bunt; 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 1B448606A32C for ; Sat, 7 Nov 2026 10:44:40 +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=VVN5bunt Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4E4991F0089F; Sat, 7 Nov 2026 10:44:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794048280; bh=pElnO3z2wuOHoD7Ln3dqX3KX5P995BBlt3Vhhft2FlE=; h=From:To:Cc:Subject:Date; b=VVN5buntvGt9ZmIr5STGbt+IxLk/1HeD8fSdKw7DKLWNnDv830su4K+BEtiNJG53x Ue87FahQ9OtyPbNSlgPqNJ2xHBV9Hg1KREQZvr3b3oV9n9WROamHCn+oHHL92OkfXc iyYNIN5yD55qEHuZRSV7hOCyolQtrDWbgv4hyYCYwsGZPjDpUo5Ub/KqGGGHdriCdm w1vqTWoXPTE4mXb26So7ZPryjTupAxzbCyUBGGXqyYX39MYl39BdNWPD1bBy4if+HE DzmNwAgFrUOyu8BWsaPloH50rHVlOh0+opyUb0s2PyuuL4GVO2rs2gJxczTV9SnqOv JjUpYm1oIHHAw== 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 6.1-stable tree Date: Sat, 7 Nov 2026 05:44:37 -0500 Message-ID: <20261107054437-failed-6.1-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 6.1-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-6.1.y git checkout FETCH_HEAD git cherry-pick -x e234d7625598b2eaded84fa99f53c8062650828f # git commit -s git send-email --to '' --in-reply-to '20261107054437-failed-6.1-e234d7625598@kernel.org' --subject-prefix 'PATCH 6.1.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