From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9C7C9C43603 for ; Mon, 16 Dec 2019 17:51:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7454B20726 for ; Mon, 16 Dec 2019 17:51:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1576518681; bh=dMlxio4fVNiztZsJSbPZb+jiUQpKnO6vtJqb9VrvA3o=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=rnXpg9IIvdDlCA5EvAxC+JKtr+sqznPEeJQHr1l/Y8I0+5cKZQ5OreoUyCxqgqUF0 Goq9YpeVnaubJSs51412qGQcpJmISljJLr6HiLQYp0l9NGDK0PeT+oct8wmvMHW4kn FQDxdkVORUKd71Hicnx6GAMdB16MbEkQMlFAjY58= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726881AbfLPRvU (ORCPT ); Mon, 16 Dec 2019 12:51:20 -0500 Received: from mail.kernel.org ([198.145.29.99]:41218 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726833AbfLPRvS (ORCPT ); Mon, 16 Dec 2019 12:51:18 -0500 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 9418520700; Mon, 16 Dec 2019 17:51:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1576518678; bh=dMlxio4fVNiztZsJSbPZb+jiUQpKnO6vtJqb9VrvA3o=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=OPG7m4KXyncvny1jT8sEcYTlxfYBuA6XUnwjP3L4bquSvFRFVQR2v9Tgapqum25uC BhUcq0am55ux/secHOHw5beZ9TznzFEKWlngUSM5u0BpC2HsKJ6PVOd2Yrha77IDX1 I5r0FHMgNGSykZfMblE3e8v8CfGPrhmjuBtxVGwc= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Vincent Whitchurch Subject: [PATCH 4.14 006/267] serial: pl011: Fix DMA ->flush_buffer() Date: Mon, 16 Dec 2019 18:45:32 +0100 Message-Id: <20191216174849.509808434@linuxfoundation.org> X-Mailer: git-send-email 2.24.1 In-Reply-To: <20191216174848.701533383@linuxfoundation.org> References: <20191216174848.701533383@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Vincent Whitchurch commit f6a196477184b99a31d16366a8e826558aa11f6d upstream. PL011's ->flush_buffer() implementation releases and reacquires the port lock. Due to a race condition here, data can end up being added to the circular buffer but neither being discarded nor being sent out. This leads to, for example, tcdrain(2) waiting indefinitely. Process A Process B uart_flush_buffer() - acquire lock - circ_clear - pl011_flush_buffer() -- release lock -- dmaengine_terminate_all() uart_write() - acquire lock - add chars to circ buffer - start_tx() -- start DMA - release lock -- acquire lock -- turn off DMA -- release lock // Data in circ buffer but DMA is off According to the comment in the code, the releasing of the lock around dmaengine_terminate_all() is to avoid a deadlock with the DMA engine callback. However, since the time this code was written, the DMA engine API documentation seems to have been clarified to say that dmaengine_terminate_all() (in the identically implemented but differently named dmaengine_terminate_async() variant) does not wait for any running complete callback to be completed and can even be called from a complete callback. So there is no possibility of deadlock if the DMA engine driver implements this API correctly. So we should be able to just remove this release and reacquire of the lock to prevent the aforementioned race condition. Signed-off-by: Vincent Whitchurch Cc: stable Link: https://lore.kernel.org/r/20191118092547.32135-1-vincent.whitchurch@axis.com Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/amba-pl011.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) --- a/drivers/tty/serial/amba-pl011.c +++ b/drivers/tty/serial/amba-pl011.c @@ -829,10 +829,8 @@ __acquires(&uap->port.lock) if (!uap->using_tx_dma) return; - /* Avoid deadlock with the DMA engine callback */ - spin_unlock(&uap->port.lock); - dmaengine_terminate_all(uap->dmatx.chan); - spin_lock(&uap->port.lock); + dmaengine_terminate_async(uap->dmatx.chan); + if (uap->dmatx.queued) { dma_unmap_sg(uap->dmatx.chan->device->dev, &uap->dmatx.sg, 1, DMA_TO_DEVICE);