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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A0A64C433EF for ; Wed, 29 Sep 2021 21:44:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7CFA061528 for ; Wed, 29 Sep 2021 21:44:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1347110AbhI2Vpq (ORCPT ); Wed, 29 Sep 2021 17:45:46 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59470 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1346779AbhI2Vpp (ORCPT ); Wed, 29 Sep 2021 17:45:45 -0400 Received: from phobos.denx.de (phobos.denx.de [IPv6:2a01:238:438b:c500:173d:9f52:ddab:ee01]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 81A53C06161C for ; Wed, 29 Sep 2021 14:44:03 -0700 (PDT) Received: from localhost.localdomain (unknown [IPv6:2804:14c:485:504a:b573:3d62:4f2f:678d]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)) (No client certificate requested) (Authenticated sender: festevam@denx.de) by phobos.denx.de (Postfix) with ESMTPSA id 5963E80641; Wed, 29 Sep 2021 23:43:58 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=denx.de; s=phobos-20191101; t=1632951840; bh=WwGSxEGNbHzzabfmoQXzUhpuKakN+jmv23Zdt+O4BNc=; h=From:To:Cc:Subject:Date:From; b=n+sYaOTL1jk7KzvHBgyVExv39woOu9JrQShWi/gCWqDIG7z6Pt72bD5ImeRjhgfxA VBaS+hgR1Z4HCbUA9HAiMybvhHD7RS4tIX4eTKZ2wPtCMEiGOCCwf8IHUJ93/Xsfnp 7Avc0+v17Qm86HksCC/UjLpUGDpFneokjUVnfcWW8ErhMT1kToPxfllD80gYVlWOLn wrIZfKkZ5g7Qj5/VOKXVoxu8xPVzq/87kmtCHHoZB3XuU7JPpVvEt1SeQgRpSYuo5U i1ISAnMdgz3kiIj2Q8HhLicOM5lFxsCqf3rDkdkfa9RZ8CMw1i0cLlUcIDg9WtpCHS +oseZpDueQcTg== From: Fabio Estevam To: gregkh@linuxfoundation.org Cc: michael@walle.cc, linux-serial@vger.kernel.org, johan@kernel.org, marex@denx.de, Fabio Estevam Subject: [PATCH v2] serial: imx: Fix sysrq deadlock Date: Wed, 29 Sep 2021 18:43:24 -0300 Message-Id: <20210929214324.44910-1-festevam@denx.de> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Virus-Scanned: clamav-milter 0.103.2 at phobos.denx.de X-Virus-Status: Clean Precedence: bulk List-ID: X-Mailing-List: linux-serial@vger.kernel.org The following sysrq command causes the following deadlock: # echo t > /proc/sysrq-trigger .... [ 20.325246] ====================================================== [ 20.325252] WARNING: possible circular locking dependency detected [ 20.325260] 5.15.0-rc2-next-20210924-00004-gd2d6e664f29f-dirty #163 Not tainted [ 20.325273] ------------------------------------------------------ [ 20.325279] sh/236 is trying to acquire lock: [ 20.325293] c1618614 (console_owner){-...}-{0:0}, at: console_unlock+0x180/0x5bc [ 20.325361] [ 20.325361] but task is already holding lock: [ 20.325368] eefccc90 (&pool->lock){-.-.}-{2:2}, at: show_workqueue_state+0x104/0x3c8 [ 20.325432] [ 20.325432] which lock already depends on the new lock. ... [ 20.325657] -> #2 (&pool->lock/1){-.-.}-{2:2}: [ 20.325690] __queue_work+0x114/0x810 [ 20.325710] queue_work_on+0x54/0x94 [ 20.325727] __imx_uart_rxint.constprop.0+0x1b4/0x2e0 [ 20.325760] imx_uart_int+0x270/0x310 This problem happens because uart_handle_sysrq_char() is called with the lock held. Fix this by using the same approach done in commit 5697df7322fe ("serial: fsl_lpuart: split sysrq handling"), which calls uart_unlock_and_check_sysrq() to drop the lock prior to uart_handle_sysrq_char(). Signed-off-by: Fabio Estevam --- Changes since v1: - I noticed that when sending break + t via the terminal, the characters were sometimes lost. Do the minimal changes to fix the deadlock without missing the sysrq input. drivers/tty/serial/imx.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c index 8b121cd869e9..1c768dd3896d 100644 --- a/drivers/tty/serial/imx.c +++ b/drivers/tty/serial/imx.c @@ -788,6 +788,7 @@ static irqreturn_t __imx_uart_rxint(int irq, void *dev_id) unsigned int rx, flg, ignored = 0; struct tty_port *port = &sport->port.state->port; + uart_unlock_and_check_sysrq(&sport->port); while (imx_uart_readl(sport, USR2) & USR2_RDR) { u32 usr2; @@ -846,6 +847,7 @@ static irqreturn_t __imx_uart_rxint(int irq, void *dev_id) out: tty_flip_buffer_push(port); + spin_lock(&sport->port.lock); return IRQ_HANDLED; } -- 2.25.1