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 A3412C433F5 for ; Sun, 17 Oct 2021 10:42:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8524A60F56 for ; Sun, 17 Oct 2021 10:42:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242133AbhJQKot (ORCPT ); Sun, 17 Oct 2021 06:44:49 -0400 Received: from mail.kernel.org ([198.145.29.99]:55456 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S242117AbhJQKos (ORCPT ); Sun, 17 Oct 2021 06:44:48 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id BBBDD604DB; Sun, 17 Oct 2021 10:42:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1634467359; bh=IQC5YAXiA32y+YJueqAwkeq/zb2ETlnoZG6erDdXXx8=; h=Subject:To:Cc:From:Date:From; b=UOoIFZrKfij1zQt4QUracdbhl/zqs8T3qx7Zpv0ev2pfWDuLQAmyKPPktTEhSNP/b 5q9XHkjLdUPi0GrqNip+Gdrt9v3qxuJ2uqpibK/7hGYk3vGh6IY0QU0K8GEuWRptcW +43aKBwMoyxVDf4abtOoweSH+F7DWnYWrmAGHXb4= Subject: FAILED: patch "[PATCH] workqueue: fix state-dump console deadlock" failed to apply to 4.14-stable tree To: johan@kernel.org, festevam@denx.de, john.ogness@linutronix.de, tj@kernel.org Cc: From: Date: Sun, 17 Oct 2021 12:42:31 +0200 Message-ID: <163446735179246@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org The patch below does not apply to the 4.14-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From 57116ce17b04fde2fe30f0859df69d8dbe5809f6 Mon Sep 17 00:00:00 2001 From: Johan Hovold Date: Wed, 6 Oct 2021 13:58:52 +0200 Subject: [PATCH] workqueue: fix state-dump console deadlock Console drivers often queue work while holding locks also taken in their console write paths, something which can lead to deadlocks on SMP when dumping workqueue state (e.g. sysrq-t or on suspend failures). For serial console drivers this could look like: CPU0 CPU1 ---- ---- show_workqueue_state(); lock(&pool->lock); lock(&port->lock); schedule_work(); lock(&pool->lock); printk(); lock(console_owner); lock(&port->lock); where workqueues are, for example, used to push data to the line discipline, process break signals and handle modem-status changes. Line disciplines and serdev drivers can also queue work on write-wakeup notifications, etc. Reworking every console driver to avoid queuing work while holding locks also taken in their write paths would complicate drivers and is neither desirable or feasible. Instead use the deferred-printk mechanism to avoid printing while holding pool locks when dumping workqueue state. Note that there are a few WARN_ON() assertions in the workqueue code which could potentially also trigger a deadlock. Hopefully the ongoing printk rework will provide a general solution for this eventually. This was originally reported after a lockdep splat when executing sysrq-t with the imx serial driver. Fixes: 3494fc30846d ("workqueue: dump workqueues on sysrq-t") Cc: stable@vger.kernel.org # 4.0 Reported-by: Fabio Estevam Tested-by: Fabio Estevam Signed-off-by: Johan Hovold Reviewed-by: John Ogness Signed-off-by: Tejun Heo diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 33a6b4a2443d..1b3eb1e9531f 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -4830,8 +4830,16 @@ void show_workqueue_state(void) for_each_pwq(pwq, wq) { raw_spin_lock_irqsave(&pwq->pool->lock, flags); - if (pwq->nr_active || !list_empty(&pwq->inactive_works)) + if (pwq->nr_active || !list_empty(&pwq->inactive_works)) { + /* + * Defer printing to avoid deadlocks in console + * drivers that queue work while holding locks + * also taken in their write paths. + */ + printk_deferred_enter(); show_pwq(pwq); + printk_deferred_exit(); + } raw_spin_unlock_irqrestore(&pwq->pool->lock, flags); /* * We could be printing a lot from atomic context, e.g. @@ -4849,7 +4857,12 @@ void show_workqueue_state(void) raw_spin_lock_irqsave(&pool->lock, flags); if (pool->nr_workers == pool->nr_idle) goto next_pool; - + /* + * Defer printing to avoid deadlocks in console drivers that + * queue work while holding locks also taken in their write + * paths. + */ + printk_deferred_enter(); pr_info("pool %d:", pool->id); pr_cont_pool_info(pool); pr_cont(" hung=%us workers=%d", @@ -4864,6 +4877,7 @@ void show_workqueue_state(void) first = false; } pr_cont("\n"); + printk_deferred_exit(); next_pool: raw_spin_unlock_irqrestore(&pool->lock, flags); /*