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,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable 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 C1118C43603 for ; Wed, 11 Dec 2019 15:07:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 94645222C4 for ; Wed, 11 Dec 2019 15:07:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1576076853; bh=pQakcmBqFDRLENctK9bfXEUWLJiw418Ya1RuBaWljTQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=UP72eM/SqLvcfNK8W9CPBrvWHmLCp7AgjZ2l8QEW+nP9jdKGijdmrSfEpdTVtZnFz ltWA12yKyE4lnqbBlnDhXjmUbkmGvTF2XbB+i7SBxV1kocLHLDnjyEOtF3Y5cpEqka LUu2qNoVYC58JfgJC1FNFpTMAUZqWhRJ7ZlX6JiA= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729983AbfLKPHc (ORCPT ); Wed, 11 Dec 2019 10:07:32 -0500 Received: from mail.kernel.org ([198.145.29.99]:54580 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729912AbfLKPH3 (ORCPT ); Wed, 11 Dec 2019 10:07:29 -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 8648320663; Wed, 11 Dec 2019 15:07:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1576076848; bh=pQakcmBqFDRLENctK9bfXEUWLJiw418Ya1RuBaWljTQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=kZlALQH7DcptGfsmLHOoNW5xNfaT03U85iw+Swets9M8vP/edZN/qOkP5pnlHZvpe 1CFvQ010aE/BFdJQeDX0PA72MjM9YFq6oTtLdPdt2yG/fYK58OJJTTziSvgyrOqmEN gkoeoZrnhSLvJKpQ/GPiolKykp0J8HW7w3p8MTlc= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Vincent Whitchurch Subject: [PATCH 5.4 14/92] serial: pl011: Fix DMA ->flush_buffer() Date: Wed, 11 Dec 2019 16:05:05 +0100 Message-Id: <20191211150225.289829149@linuxfoundation.org> X-Mailer: git-send-email 2.24.1 In-Reply-To: <20191211150221.977775294@linuxfoundation.org> References: <20191211150221.977775294@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);