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 82B5CC00454 for ; Wed, 11 Dec 2019 15:54:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 522502073B for ; Wed, 11 Dec 2019 15:54:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1576079694; bh=pQakcmBqFDRLENctK9bfXEUWLJiw418Ya1RuBaWljTQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=ZPsYuwPofHXSW45X06Ch8FuuJbGkOsUEAWzCTbj0wbC83X8VuXLvOi+aOR1Uob1wh 1mKqyjc/5wQtV+OQ5ED8Bd+tDgnjsxtiRrHU3RsaTW+AuanPfsq5d4INwxrAPQrqlw veACL3YUKI3LoR35JQF/MKoSijxp49xny9R+VwTo= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731970AbfLKPRE (ORCPT ); Wed, 11 Dec 2019 10:17:04 -0500 Received: from mail.kernel.org ([198.145.29.99]:44306 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731790AbfLKPRA (ORCPT ); Wed, 11 Dec 2019 10:17:00 -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 A2BD720663; Wed, 11 Dec 2019 15:16:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1576077420; bh=pQakcmBqFDRLENctK9bfXEUWLJiw418Ya1RuBaWljTQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=dPfBQtc5C5gW9FUpZS7Dhe9+/DCn/3dsO/pk5Vv8VdtYcFwGxYMM6yO4syIBJ1fco HDIwwaEgltlOBVhOc/efmJsM36NraZuWNNYgtPhtplNEEyHked7RVf+6jefe56rhs9 CXI/+NUHpVJNQY1KuVTXrTK8Z1WSY69b/7dlklso= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Vincent Whitchurch Subject: [PATCH 4.19 008/243] serial: pl011: Fix DMA ->flush_buffer() Date: Wed, 11 Dec 2019 16:02:50 +0100 Message-Id: <20191211150339.685757300@linuxfoundation.org> X-Mailer: git-send-email 2.24.1 In-Reply-To: <20191211150339.185439726@linuxfoundation.org> References: <20191211150339.185439726@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 @@ -813,10 +813,8 @@ __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);