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=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,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 AE068C4332B for ; Thu, 19 Mar 2020 00:12:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 84E532076F for ; Thu, 19 Mar 2020 00:12:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1584576734; bh=TdhN6iEu3ZBiSuFW3OU6H5q6ejlclIc2O1HRtdN/Aa8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=j+dnofDLFHHlnsIseyR4Nxr0Qig+qN3GJKxS5lBatUo4tMDfndPdAqa5GDGDuag71 GB69fUzpWMrL4YTj4zfM4pktQLGpfM5Rc8B8VRJwrwT73z9zUTMnbgEPmDp6VWX3wN y/k/XZ0OuMNFMrQrWIBIZoclLcUNQ9XiCGR+uuMk= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726596AbgCSALD (ORCPT ); Wed, 18 Mar 2020 20:11:03 -0400 Received: from mail.kernel.org ([198.145.29.99]:36984 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726856AbgCSALD (ORCPT ); Wed, 18 Mar 2020 20:11:03 -0400 Received: from paulmck-ThinkPad-P72.home (50-39-105-78.bvtn.or.frontiernet.net [50.39.105.78]) (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 6BA722076F; Thu, 19 Mar 2020 00:11:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1584576662; bh=TdhN6iEu3ZBiSuFW3OU6H5q6ejlclIc2O1HRtdN/Aa8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=fbNqqMg3Oqpklu8K0G5iDCZQhtBX01G/nCi7767V73PjXv2RZBfRyvNDMP5dBYkZ/ n8BbHfpOl9GPQ+NIXMGMzgPLsT2styP0+B8Fzhjs2/MJ+8wwTS2nsOmAUQaSe+zeyB YuGkhaPeNByPQWX4rZl6ESLMggQrf0cMHwBojcOA= 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, dipankar@in.ibm.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 RFC v2 tip/core/rcu 02/22] rcu: Add per-task state to RCU CPU stall warnings Date: Wed, 18 Mar 2020 17:10:40 -0700 Message-Id: <20200319001100.24917-2-paulmck@kernel.org> X-Mailer: git-send-email 2.9.5 In-Reply-To: <20200319001024.GA28798@paulmck-ThinkPad-P72> References: <20200319001024.GA28798@paulmck-ThinkPad-P72> Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org From: "Paul E. McKenney" Currently, an RCU-preempt CPU stall warning simply lists the PIDs of those tasks holding up the current grace period. This can be helpful, but more can be even more helpful. To this end, this commit adds the nesting level, whether the task things it was preempted in its current RCU read-side critical section, whether RCU core has asked this task for a quiescent state, whether the expedited-grace-period hint is set, and whether the task believes that it is on the blocked-tasks list (it must be, or it would not be printed, but if things are broken, best not to take too much for granted). Signed-off-by: Paul E. McKenney --- kernel/rcu/tree_stall.h | 38 ++++++++++++++++++++++++++++++++++++-- 1 file changed, 36 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h index 502b4dd..e19487d 100644 --- a/kernel/rcu/tree_stall.h +++ b/kernel/rcu/tree_stall.h @@ -192,14 +192,40 @@ static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp) raw_spin_unlock_irqrestore_rcu_node(rnp, flags); } +// Communicate task state back to the RCU CPU stall warning request. +struct rcu_stall_chk_rdr { + int nesting; + union rcu_special rs; + bool on_blkd_list; +}; + +/* + * Report out the state of a not-running task that is stalling the + * current RCU grace period. + */ +static bool check_slow_task(struct task_struct *t, void *arg) +{ + struct rcu_node *rnp; + struct rcu_stall_chk_rdr *rscrp = arg; + + if (task_curr(t)) + return false; // It is running, so decline to inspect it. + rscrp->nesting = t->rcu_read_lock_nesting; + rscrp->rs = t->rcu_read_unlock_special; + rnp = t->rcu_blocked_node; + rscrp->on_blkd_list = !list_empty(&t->rcu_node_entry); + return true; +} + /* * Scan the current list of tasks blocked within RCU read-side critical * sections, printing out the tid of each. */ static int rcu_print_task_stall(struct rcu_node *rnp) { - struct task_struct *t; int ndetected = 0; + struct rcu_stall_chk_rdr rscr; + struct task_struct *t; if (!rcu_preempt_blocked_readers_cgp(rnp)) return 0; @@ -208,7 +234,15 @@ 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) { - pr_cont(" P%d", t->pid); + if (!try_invoke_on_locked_down_task(t, check_slow_task, &rscr)) + pr_cont(" P%d", t->pid); + else + pr_cont(" P%d/%d:%c%c%c%c", + t->pid, rscr.nesting, + ".b"[rscr.rs.b.blocked], + ".q"[rscr.rs.b.need_qs], + ".e"[rscr.rs.b.exp_hint], + ".l"[rscr.on_blkd_list]); ndetected++; } pr_cont("\n"); -- 2.9.5