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 0FEAB3AD527; Mon, 23 Mar 2026 13:52:32 +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=1774273952; cv=none; b=lgevun+Y+ud1DYl+gHst0Yswb7WEKOEregsOJke1X5Z7W6tkGgFNcn1C9gsnE56OZsof+PmzwuM+QIPulMLTRv8+BH+fkVpi//3elFeA6Ivem3RSE1hvPbxkW9qiEq12yIPgja2psxOXDE73HbnZDPOevL0sCyAgt4etmeaef4w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774273952; c=relaxed/simple; bh=61grHwQ/vLnx4N/BrpNwyK2y+GikjA6u40rue9ZUaUA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=iabsTIR6uKf+ZPGFF79NzUPFl96RFkBPewrZzgynaNXF+KpygesoZZQBWRLZd2nMiu+x21hwb07Py4YrT6RkKalDk/JvepGkE2lhS1cEsob40l8pF/UROUURkpLhydV8sGL7dA8+tc2+lj54fsEtE0Puj135c1HJGhdasBCzsCg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=k5lUBUiW; 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="k5lUBUiW" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8732DC4CEF7; Mon, 23 Mar 2026 13:52:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1774273951; bh=61grHwQ/vLnx4N/BrpNwyK2y+GikjA6u40rue9ZUaUA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=k5lUBUiWi3bPZ9Gf/5aqWDvf8vL/zNJ34G6zWiE+vfL/0PGQnvvUsyOWtiFnO4KIM zBV+c3LGbaR0BD6OVDYC+7MngubYg/mZJ07lGoxp1My5xMw9mDWbAnsCmH7tL1DYF8 gSQLQXenC1CewHR3jFBCQptAN1f3QnCLGiyO729A= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, stable , Raul E Rangel Subject: [PATCH 6.19 060/220] serial: 8250: Fix TX deadlock when using DMA Date: Mon, 23 Mar 2026 14:43:57 +0100 Message-ID: <20260323134506.486952925@linuxfoundation.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260323134504.575022936@linuxfoundation.org> References: <20260323134504.575022936@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.19-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 @@ -162,7 +162,22 @@ 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)