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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D1018C433EF for ; Wed, 20 Apr 2022 06:16:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1359496AbiDTGTP (ORCPT ); Wed, 20 Apr 2022 02:19:15 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38976 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1359480AbiDTGTI (ORCPT ); Wed, 20 Apr 2022 02:19:08 -0400 Received: from mail-pl1-x631.google.com (mail-pl1-x631.google.com [IPv6:2607:f8b0:4864:20::631]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C4870393DB for ; Tue, 19 Apr 2022 23:16:23 -0700 (PDT) Received: by mail-pl1-x631.google.com with SMTP id s14so900970plk.8 for ; Tue, 19 Apr 2022 23:16:23 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=nrmZN1YGOXwt96xOgDckyKdEp0sX0UQnyV38Md8fDGs=; b=bHBqeh+CrW9h20RGBZXkWpQvf8YwJDwRfjQbGqhVknLEACTwHhEFaqmd+4l3Ptfxza EH+vqfFNLManK+QQZpss9gjUc5sa4qLUw58mojbTvaS0INZipA6XoRm/Ya7F4FtG7Wit Uyf2UqDky9RIWj9xOQdq/xcxbvdoPRvCbyR6D81bsw9ihcmPykjPgTGlB3UpVh7UYSXO L0KtEzQD8e3StZ862FvNcchsX569ksD90vwg3fFJCQk/TdPVzP8SnmiTfHqcoTE5+8n8 574kbXlWpTmaISmD9nVClw4EETxiiNS1Gn++gl0sF7IFhWKNnxDA/FJYeilTaX2VXWAp ThDQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=nrmZN1YGOXwt96xOgDckyKdEp0sX0UQnyV38Md8fDGs=; b=GZeemRLiQZo7i4zfiDaxB4bdvR9X1iSNOHwTaqE7xqrtPS2CHRg8IJMFbGFcLupztm rE8p+U+uwywdLow6LoObK7d1G4VcCz2PBHx0S5a3gOY0wDzHKi8+w4gEVJ+wEWDs8wBd 5HFgQidLNQ/KyUWn3ecYMLVDzoE0YlagdNrmXfD2Gxbf3RZK+vxg4hjhV6mCLS+BX93b Glxyo3mjAXrCJpduTvKqy/gsA2a+iW1aUYKWcoFa6Jm9l6lPFqr4VPY/madXkk0pSIX8 8dpBRXc+4CfyXk4DhCjxIwrsEB3Yc89AwVxGhxAwPeO+YTor1KQQ916M7d1R+qkd4EET hd9g== X-Gm-Message-State: AOAM53331hKhhtk0Ix1mnww30F7RsSmFMMfCmmvIw2Qal9P8SPdH6nU7 LVavA02pjcnHYUany/DLTTc= X-Google-Smtp-Source: ABdhPJzsrUQ6zA4RClsX41beCZK8xWPN5bmsPvGtAMLQAsLGHZDSBcFO1TBTgkG8has8I8lBOqtAkw== X-Received: by 2002:a17:90b:4d86:b0:1d2:cd59:d275 with SMTP id oj6-20020a17090b4d8600b001d2cd59d275mr2589745pjb.119.1650435383187; Tue, 19 Apr 2022 23:16:23 -0700 (PDT) Received: from octofox.hsd1.ca.comcast.net ([2601:641:401:1d20:daec:60d:88f6:798a]) by smtp.gmail.com with ESMTPSA id k22-20020aa790d6000000b0050a765d5d48sm9798778pfk.160.2022.04.19.23.16.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 19 Apr 2022 23:16:22 -0700 (PDT) From: Max Filippov To: Linus Torvalds Cc: linux-kernel@vger.kernel.org, linux-xtensa@linux-xtensa.org, Chris Zankel , Duoming Zhou , Max Filippov Subject: [PATCH 2/3] arch: xtensa: platforms: Fix deadlock in rs_close() Date: Tue, 19 Apr 2022 23:16:10 -0700 Message-Id: <20220420061611.4103443-3-jcmvbkbc@gmail.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20220420061611.4103443-1-jcmvbkbc@gmail.com> References: <20220420061611.4103443-1-jcmvbkbc@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Duoming Zhou There is a deadlock in rs_close(), which is shown below: (Thread 1) | (Thread 2) | rs_open() rs_close() | mod_timer() spin_lock_bh() //(1) | (wait a time) ... | rs_poll() del_timer_sync() | spin_lock() //(2) (wait timer to stop) | ... We hold timer_lock in position (1) of thread 1 and use del_timer_sync() to wait timer to stop, but timer handler also need timer_lock in position (2) of thread 2. As a result, rs_close() will block forever. This patch deletes the redundant timer_lock in order to prevent the deadlock. Because there is no race condition between rs_close, rs_open and rs_poll. Signed-off-by: Duoming Zhou Message-Id: <20220407154430.22387-1-duoming@zju.edu.cn> Signed-off-by: Max Filippov --- arch/xtensa/platforms/iss/console.c | 8 -------- 1 file changed, 8 deletions(-) diff --git a/arch/xtensa/platforms/iss/console.c b/arch/xtensa/platforms/iss/console.c index 81d7c7e8f7e9..10b79d3c74e0 100644 --- a/arch/xtensa/platforms/iss/console.c +++ b/arch/xtensa/platforms/iss/console.c @@ -36,24 +36,19 @@ static void rs_poll(struct timer_list *); static struct tty_driver *serial_driver; static struct tty_port serial_port; static DEFINE_TIMER(serial_timer, rs_poll); -static DEFINE_SPINLOCK(timer_lock); static int rs_open(struct tty_struct *tty, struct file * filp) { - spin_lock_bh(&timer_lock); if (tty->count == 1) mod_timer(&serial_timer, jiffies + SERIAL_TIMER_VALUE); - spin_unlock_bh(&timer_lock); return 0; } static void rs_close(struct tty_struct *tty, struct file * filp) { - spin_lock_bh(&timer_lock); if (tty->count == 1) del_timer_sync(&serial_timer); - spin_unlock_bh(&timer_lock); } @@ -73,8 +68,6 @@ static void rs_poll(struct timer_list *unused) int rd = 1; unsigned char c; - spin_lock(&timer_lock); - while (simc_poll(0)) { rd = simc_read(0, &c, 1); if (rd <= 0) @@ -87,7 +80,6 @@ static void rs_poll(struct timer_list *unused) tty_flip_buffer_push(port); if (rd) mod_timer(&serial_timer, jiffies + SERIAL_TIMER_VALUE); - spin_unlock(&timer_lock); } -- 2.30.2