From patchwork Thu May 20 09:20:15 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg Kroah-Hartman X-Patchwork-Id: 445710 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=-19.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER, INCLUDES_PATCH, MAILING_LIST_MULTI, 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 D67F2C433B4 for ; Thu, 20 May 2021 09:59:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BA79761CBE for ; Thu, 20 May 2021 09:59:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234590AbhETKAU (ORCPT ); Thu, 20 May 2021 06:00:20 -0400 Received: from mail.kernel.org ([198.145.29.99]:59460 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234944AbhETJ6E (ORCPT ); Thu, 20 May 2021 05:58:04 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 6817B6141A; Thu, 20 May 2021 09:38:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1621503495; bh=b2NNR4uP4F02APtRG8iQHi3KAfZ/MjewFXSKxbehxi4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=XucJsiM6t+5oCUIeVEX4doPGSwKIWjV4oVHzRIaVZ1c5t6Okm+XrzC3Qk/NNmjcPf NC4jK++/3bIC47TdWwx0fhfk62+tyB90jTK6lad2vl0QlkUJ9CvDLeeg5B/KL131n3 4D5lPo4HBg28uSTCWbunaD0VQx5WMu9F2jGdxq7E= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Peter Zijlstra , Waiman Long , Sasha Levin Subject: [PATCH 4.19 246/425] sched/debug: Fix cgroup_path[] serialization Date: Thu, 20 May 2021 11:20:15 +0200 Message-Id: <20210520092139.504967137@linuxfoundation.org> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20210520092131.308959589@linuxfoundation.org> References: <20210520092131.308959589@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Waiman Long [ Upstream commit ad789f84c9a145f8a18744c0387cec22ec51651e ] The handling of sysrq key can be activated by echoing the key to /proc/sysrq-trigger or via the magic key sequence typed into a terminal that is connected to the system in some way (serial, USB or other mean). In the former case, the handling is done in a user context. In the latter case, it is likely to be in an interrupt context. Currently in print_cpu() of kernel/sched/debug.c, sched_debug_lock is taken with interrupt disabled for the whole duration of the calls to print_*_stats() and print_rq() which could last for the quite some time if the information dump happens on the serial console. If the system has many cpus and the sched_debug_lock is somehow busy (e.g. parallel sysrq-t), the system may hit a hard lockup panic depending on the actually serial console implementation of the system. The purpose of sched_debug_lock is to serialize the use of the global cgroup_path[] buffer in print_cpu(). The rests of the printk calls don't need serialization from sched_debug_lock. Calling printk() with interrupt disabled can still be problematic if multiple instances are running. Allocating a stack buffer of PATH_MAX bytes is not feasible because of the limited size of the kernel stack. The solution implemented in this patch is to allow only one caller at a time to use the full size group_path[], while other simultaneous callers will have to use shorter stack buffers with the possibility of path name truncation. A "..." suffix will be printed if truncation may have happened. The cgroup path name is provided for informational purpose only, so occasional path name truncation should not be a big problem. Fixes: efe25c2c7b3a ("sched: Reinstate group names in /proc/sched_debug") Suggested-by: Peter Zijlstra Signed-off-by: Waiman Long Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20210415195426.6677-1-longman@redhat.com Signed-off-by: Sasha Levin --- kernel/sched/debug.c | 42 +++++++++++++++++++++++++++++------------- 1 file changed, 29 insertions(+), 13 deletions(-) diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c index 78fadf0438ea..9518606fa1e5 100644 --- a/kernel/sched/debug.c +++ b/kernel/sched/debug.c @@ -11,8 +11,6 @@ */ #include "sched.h" -static DEFINE_SPINLOCK(sched_debug_lock); - /* * This allows printing both to /proc/sched_debug and * to the console @@ -434,16 +432,37 @@ static void print_cfs_group_stats(struct seq_file *m, int cpu, struct task_group #endif #ifdef CONFIG_CGROUP_SCHED +static DEFINE_SPINLOCK(sched_debug_lock); static char group_path[PATH_MAX]; -static char *task_group_path(struct task_group *tg) +static void task_group_path(struct task_group *tg, char *path, int plen) { - if (autogroup_path(tg, group_path, PATH_MAX)) - return group_path; + if (autogroup_path(tg, path, plen)) + return; - cgroup_path(tg->css.cgroup, group_path, PATH_MAX); + cgroup_path(tg->css.cgroup, path, plen); +} - return group_path; +/* + * Only 1 SEQ_printf_task_group_path() caller can use the full length + * group_path[] for cgroup path. Other simultaneous callers will have + * to use a shorter stack buffer. A "..." suffix is appended at the end + * of the stack buffer so that it will show up in case the output length + * matches the given buffer size to indicate possible path name truncation. + */ +#define SEQ_printf_task_group_path(m, tg, fmt...) \ +{ \ + if (spin_trylock(&sched_debug_lock)) { \ + task_group_path(tg, group_path, sizeof(group_path)); \ + SEQ_printf(m, fmt, group_path); \ + spin_unlock(&sched_debug_lock); \ + } else { \ + char buf[128]; \ + char *bufend = buf + sizeof(buf) - 3; \ + task_group_path(tg, buf, bufend - buf); \ + strcpy(bufend - 1, "..."); \ + SEQ_printf(m, fmt, buf); \ + } \ } #endif @@ -470,7 +489,7 @@ print_task(struct seq_file *m, struct rq *rq, struct task_struct *p) SEQ_printf(m, " %d %d", task_node(p), task_numa_group_id(p)); #endif #ifdef CONFIG_CGROUP_SCHED - SEQ_printf(m, " %s", task_group_path(task_group(p))); + SEQ_printf_task_group_path(m, task_group(p), " %s") #endif SEQ_printf(m, "\n"); @@ -507,7 +526,7 @@ void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq) #ifdef CONFIG_FAIR_GROUP_SCHED SEQ_printf(m, "\n"); - SEQ_printf(m, "cfs_rq[%d]:%s\n", cpu, task_group_path(cfs_rq->tg)); + SEQ_printf_task_group_path(m, cfs_rq->tg, "cfs_rq[%d]:%s\n", cpu); #else SEQ_printf(m, "\n"); SEQ_printf(m, "cfs_rq[%d]:\n", cpu); @@ -579,7 +598,7 @@ void print_rt_rq(struct seq_file *m, int cpu, struct rt_rq *rt_rq) { #ifdef CONFIG_RT_GROUP_SCHED SEQ_printf(m, "\n"); - SEQ_printf(m, "rt_rq[%d]:%s\n", cpu, task_group_path(rt_rq->tg)); + SEQ_printf_task_group_path(m, rt_rq->tg, "rt_rq[%d]:%s\n", cpu); #else SEQ_printf(m, "\n"); SEQ_printf(m, "rt_rq[%d]:\n", cpu); @@ -631,7 +650,6 @@ void print_dl_rq(struct seq_file *m, int cpu, struct dl_rq *dl_rq) static void print_cpu(struct seq_file *m, int cpu) { struct rq *rq = cpu_rq(cpu); - unsigned long flags; #ifdef CONFIG_X86 { @@ -690,13 +708,11 @@ do { \ } #undef P - spin_lock_irqsave(&sched_debug_lock, flags); print_cfs_stats(m, cpu); print_rt_stats(m, cpu); print_dl_stats(m, cpu); print_rq(m, rq, cpu); - spin_unlock_irqrestore(&sched_debug_lock, flags); SEQ_printf(m, "\n"); }