From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7FFFE3093B2; Mon, 13 Apr 2026 16:27:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776097625; cv=none; b=Sicoap6cvdLWCuYj8XX+B6dpdh1f+o5K8/HXpCGYmTnXMEj/VkB3s5aeejN6+rd57XU0eT88CFYt5jLG6Dp4vzwR/nZXcs1N4QkS9dW/o8+6yDeHUL1Pcn49V2ILrlhXjdH8lEog9tAbAAnsxvFTAAaOm7FSl3Af886tYdZsjPM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776097625; c=relaxed/simple; bh=VSp9Z7Joel7cAInllUSf43fjxNyr8KtejRsOnp0f52E=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=M4imI9Rwcg7NAhkpOeHLUwzIkL6YQYfs4Z+UdUbfQtwQuF78wC+FF5RDfi/kztsd9WpQjGZbsUIgxf3ZngOFcnvB8/BxAALEmNpQTt0G3i1txI5AM7UvfRJYuATNWs5H9/BI9qBwHNbP3Czk1ILtHv5gDqzWgtSL03ckIeLdijc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=JMvQ7I8G; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="JMvQ7I8G" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 15EE9C2BCAF; Mon, 13 Apr 2026 16:27:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1776097625; bh=VSp9Z7Joel7cAInllUSf43fjxNyr8KtejRsOnp0f52E=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=JMvQ7I8Gm45G+D3UmbDw8tc0EO0nL4D51+2BtT+C1gSNmqCPkW0er2qmW7k1dg7uc z1Kd2p4BDNjEd7SGzpfxgYRStACRzOUYQhpbObwZouj/mVlhoRC4qvzdFbeXHhQnC3 LnMbnAXOTYiUzebLwJsrc9gwW29CPyWTAfaLZJQ4= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, stable , Raul E Rangel Subject: [PATCH 5.15 210/570] serial: 8250: Fix TX deadlock when using DMA Date: Mon, 13 Apr 2026 17:55:41 +0200 Message-ID: <20260413155838.324491566@linuxfoundation.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260413155830.386096114@linuxfoundation.org> References: <20260413155830.386096114@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 5.15-stable review patch. If anyone has any objections, please let me know. ------------------ From: Raul E Rangel commit a424a34b8faddf97b5af41689087e7a230f79ba7 upstream. `dmaengine_terminate_async` does not guarantee that the `__dma_tx_complete` callback will run. The callback is currently the only place where `dma->tx_running` gets cleared. If the transaction is canceled and the callback never runs, then `dma->tx_running` will never get cleared and we will never schedule new TX DMA transactions again. This change makes it so we clear `dma->tx_running` after we terminate the DMA transaction. This is "safe" because `serial8250_tx_dma_flush` is holding the UART port lock. The first thing the callback does is also grab the UART port lock, so access to `dma->tx_running` is serialized. Fixes: 9e512eaaf8f4 ("serial: 8250: Fix fifo underflow on flush") Cc: stable Signed-off-by: Raul E Rangel Link: https://patch.msgid.link/20260209135815.1.I16366ecb0f62f3c96fe3dd5763fcf6f3c2b4d8cd@changeid Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/8250/8250_dma.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) --- a/drivers/tty/serial/8250/8250_dma.c +++ b/drivers/tty/serial/8250/8250_dma.c @@ -150,7 +150,22 @@ void serial8250_tx_dma_flush(struct uart */ dma->tx_size = 0; + /* + * We can't use `dmaengine_terminate_sync` because `uart_flush_buffer` is + * holding the uart port spinlock. + */ dmaengine_terminate_async(dma->txchan); + + /* + * The callback might or might not run. If it doesn't run, we need to ensure + * that `tx_running` is cleared so that we can schedule new transactions. + * If it does run, then the zombie callback will clear `tx_running` again + * and perform a no-op since `tx_size` was cleared above. + * + * In either case, we ASSUME the DMA transaction will terminate before we + * issue a new `serial8250_tx_dma`. + */ + dma->tx_running = 0; } int serial8250_rx_dma(struct uart_8250_port *p)