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=-13.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,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 2F01CC388F7 for ; Thu, 5 Nov 2020 23:10:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DE26620719 for ; Thu, 5 Nov 2020 23:10:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604617823; bh=cLiAusonPv4tCQb0QUWkF5lsOrakxhbxXbRLovsOtas=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=vsoEbbFgM4pKciATqh2j8lDXi40qsCj+/vxYM3nOjF8aYstM2Mifv7517+FvXy/W6 Zr4irZ+5XaqSrKV1gy3j6NB4oU65zwhi92PSamj0PPioYXvFrafQIUNXjdrDdikC9W y0s0CUi9vYuECYN0aHirZRWhzD9qUHFl5b0oJ2eo= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732475AbgKEXJZ (ORCPT ); Thu, 5 Nov 2020 18:09:25 -0500 Received: from mail.kernel.org ([198.145.29.99]:34364 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726801AbgKEXJY (ORCPT ); Thu, 5 Nov 2020 18:09:24 -0500 Received: from paulmck-ThinkPad-P72.home (50-39-104-11.bvtn.or.frontiernet.net [50.39.104.11]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 7F74920715; Thu, 5 Nov 2020 23:09:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604617763; bh=cLiAusonPv4tCQb0QUWkF5lsOrakxhbxXbRLovsOtas=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=jJQdcD1aw6BRs37FdhQuxUotiIFH8Mb7rRArI4oar9fC0luu1RL0yWRtpDAzdBcgm s699IHQ2o9xZ0EHTtu2o4aahUKIMOEXAkGbV6nvM+THmGpila7vG7uv5sXlIM3BZoD t/HmHap28uUmY7SfYXwMvy85iYje4FuJ48q4tWa0= From: paulmck@kernel.org To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com, mingo@kernel.org, jiangshanlai@gmail.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 01/16] rcu: Don't invoke try_invoke_on_locked_down_task() with irqs disabled Date: Thu, 5 Nov 2020 15:09:06 -0800 Message-Id: <20201105230921.19017-1-paulmck@kernel.org> X-Mailer: git-send-email 2.9.5 In-Reply-To: <20201105230856.GA18904@paulmck-ThinkPad-P72> References: <20201105230856.GA18904@paulmck-ThinkPad-P72> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Paul E. McKenney" The try_invoke_on_locked_down_task() function requires that interrupts be enabled, but it is called with interrupts disabled from rcu_print_task_stall(), resulting in an "IRQs not enabled as expected" diagnostic. This commit therefore updates rcu_print_task_stall() to accumulate a list of the first few tasks while holding the current leaf rcu_node structure's ->lock, then releases that lock and only then uses try_invoke_on_locked_down_task() to attempt to obtain per-task detailed information. Of course, as soon as ->lock is released, the task might exit, so the get_task_struct() function is used to prevent the task structure from going away in the meantime. Link: https://lore.kernel.org/lkml/000000000000903d5805ab908fc4@google.com/ Reported-by: syzbot+cb3b69ae80afd6535b0e@syzkaller.appspotmail.com Reported-by: syzbot+f04854e1c5c9e913cc27@syzkaller.appspotmail.com Tested-by: Sebastian Andrzej Siewior Signed-off-by: Paul E. McKenney --- kernel/rcu/tree_stall.h | 22 +++++++++++++++++----- 1 file changed, 17 insertions(+), 5 deletions(-) diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h index 0fde39b..ca21d28 100644 --- a/kernel/rcu/tree_stall.h +++ b/kernel/rcu/tree_stall.h @@ -249,13 +249,16 @@ static bool check_slow_task(struct task_struct *t, void *arg) /* * Scan the current list of tasks blocked within RCU read-side critical - * sections, printing out the tid of each. + * sections, printing out the tid of each of the first few of them. */ -static int rcu_print_task_stall(struct rcu_node *rnp) +static int rcu_print_task_stall(struct rcu_node *rnp, unsigned long flags) + __releases(rnp->lock) { + int i = 0; int ndetected = 0; struct rcu_stall_chk_rdr rscr; struct task_struct *t; + struct task_struct *ts[8]; if (!rcu_preempt_blocked_readers_cgp(rnp)) return 0; @@ -264,6 +267,14 @@ static int rcu_print_task_stall(struct rcu_node *rnp) t = list_entry(rnp->gp_tasks->prev, struct task_struct, rcu_node_entry); list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) { + get_task_struct(t); + ts[i++] = t; + if (i >= ARRAY_SIZE(ts)) + break; + } + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); + for (i--; i; i--) { + t = ts[i]; if (!try_invoke_on_locked_down_task(t, check_slow_task, &rscr)) pr_cont(" P%d", t->pid); else @@ -273,6 +284,7 @@ static int rcu_print_task_stall(struct rcu_node *rnp) ".q"[rscr.rs.b.need_qs], ".e"[rscr.rs.b.exp_hint], ".l"[rscr.on_blkd_list]); + put_task_struct(t); ndetected++; } pr_cont("\n"); @@ -293,8 +305,9 @@ static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp) * Because preemptible RCU does not exist, we never have to check for * tasks blocked within RCU read-side critical sections. */ -static int rcu_print_task_stall(struct rcu_node *rnp) +static int rcu_print_task_stall(struct rcu_node *rnp, unsigned long flags) { + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); return 0; } #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ @@ -472,7 +485,6 @@ static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps) pr_err("INFO: %s detected stalls on CPUs/tasks:\n", rcu_state.name); rcu_for_each_leaf_node(rnp) { raw_spin_lock_irqsave_rcu_node(rnp, flags); - ndetected += rcu_print_task_stall(rnp); if (rnp->qsmask != 0) { for_each_leaf_node_possible_cpu(rnp, cpu) if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) { @@ -480,7 +492,7 @@ static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps) ndetected++; } } - raw_spin_unlock_irqrestore_rcu_node(rnp, flags); + ndetected += rcu_print_task_stall(rnp, flags); // Releases rnp->lock. } for_each_possible_cpu(cpu) -- 2.9.5