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=-9.7 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 4B6D2C432C0 for ; Tue, 19 Nov 2019 03:17:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1CFDF22319 for ; Tue, 19 Nov 2019 03:17:09 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="key not found in DNS" (0-bit key) header.d=codeaurora.org header.i=@codeaurora.org header.b="Y03COGNW"; dkim=pass (1024-bit key) header.d=amazonses.com header.i=@amazonses.com header.b="a1pxYQM1" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727589AbfKSDRI (ORCPT ); Mon, 18 Nov 2019 22:17:08 -0500 Received: from a27-56.smtp-out.us-west-2.amazonses.com ([54.240.27.56]:47188 "EHLO a27-56.smtp-out.us-west-2.amazonses.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727505AbfKSDRI (ORCPT ); Mon, 18 Nov 2019 22:17:08 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/simple; s=zsmsymrwgfyinv5wlfyidntwsjeeldzt; d=codeaurora.org; t=1574133427; h=From:To:Cc:Subject:Date:Message-Id; bh=DSFxMH9kT34z8Vm44Q+35fj1K2btho1KSltCLrspVFc=; b=Y03COGNWcC2E6ORRMjEM65srtvWwA6u/HdJTrLUaioYww+58Z14VNeWzPW+hoRXy a5AzOjVfbpjERHJt/fb0atoCnFd0fsKrp3sKXf5BAk9ls1bOm9yDVlQT2Gf6q7YbzRD Q746TNvQ6+wNOe0/ZyGrpkJr2l79jkNQU8hk4/Pw= DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/simple; s=gdwg2y3kokkkj5a55z2ilkup5wp5hhxx; d=amazonses.com; t=1574133427; h=From:To:Cc:Subject:Date:Message-Id:Feedback-ID; bh=DSFxMH9kT34z8Vm44Q+35fj1K2btho1KSltCLrspVFc=; b=a1pxYQM1qoFjc3UNphUru9S9B+jJaIXqSy2nYP6o9IgahlwRfT7dirxdHOYry9YG 4ibqg7jPFXJ3ZVJcGTnObS6S3SMW3mh1NNgvi+xpFJMq0l0JDIlSFZzSeK3bEJ1wUxd xOppEDtmJulhxkfa7Fhk4q9Qbud7y7gcdMyagiAQ= DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org 8D066C433A2 Authentication-Results: aws-us-west-2-caf-mail-1.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: aws-us-west-2-caf-mail-1.web.codeaurora.org; spf=none smtp.mailfrom=neeraju@codeaurora.org From: Neeraj Upadhyay To: paulmck@kernel.org, josh@joshtriplett.org, rostedt@goodmis.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, joel@joelfernandes.org Cc: linux-kernel@vger.kernel.org, gkohli@codeaurora.org, prsood@codeaurora.org, pkondeti@codeaurora.org, rcu@vger.kernel.org, Neeraj Upadhyay Subject: [PATCH v2] rcu: Fix missed wakeup of exp_wq waiters Date: Tue, 19 Nov 2019 03:17:07 +0000 Message-ID: <0101016e81a9ecb9-ce4a6425-f21d-4166-96ed-32d3700717f1-000000@us-west-2.amazonses.com> X-Mailer: git-send-email 1.9.1 X-SES-Outgoing: 2019.11.19-54.240.27.56 Feedback-ID: 1.us-west-2.CZuq2qbDmUIuT3qdvXlRHZZCpfZqZ4GtG9v3VKgRyF0=:AmazonSES Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org For the tasks waiting in exp_wq inside exp_funnel_lock(), there is a chance that they might be indefinitely blocked in below scenario: 1. There is a task waiting on exp sequence 0b'100' inside exp_funnel_lock(). This task blocks at wq index 1. synchronize_rcu_expedited() s = 0b'100' exp_funnel_lock() wait_event(rnp->exp_wq[rcu_seq_ctr(s) & 0x3] 2. The expedited grace period (which above task blocks for) completes and task (task1) holding exp_mutex queues worker and schedules out. synchronize_rcu_expedited() s = 0b'100' queue_work(rcu_gp_wq, &rew.rew_work) wake_up_worker() schedule() 3. kworker A picks up the queued work and completes the exp gp sequence and then blocks on exp_wake_mutex, which is held by another kworker, which is doing wakeups for expedited_sequence 0. rcu_exp_wait_wake() rcu_exp_wait_wake() rcu_exp_gp_seq_end(rsp) // rsp->expedited_sequence is incremented // to 0b'100' mutex_lock(&rcu_state.exp_wake_mutex) 4. task1 does not enter wait queue, as sync_exp_work_done() returns true, and releases exp_mutex. wait_event(rnp->exp_wq[rcu_seq_ctr(s) & 0x3], sync_exp_work_done(rsp, s)); mutex_unlock(&rsp->exp_mutex); 5. Next exp GP completes, and sequence number is incremented: rcu_exp_wait_wake() rcu_exp_wait_wake() rcu_exp_gp_seq_end(rsp) // rsp->expedited_sequence = 0b'200' 6. kworker A acquires exp_wake_mutex. As it uses current expedited_sequence, it wakes up workers from wrong wait queue index - it should have worken wait queue corresponding to 0b'100' sequence, but wakes up the ones for 0b'200' sequence. This results in task at step 1 indefinitely blocked. rcu_exp_wait_wake() wake_up_all(&rnp->exp_wq[rcu_seq_ctr(rsp->expedited_sequence) & 0x3]); This issue manifested as DPM device timeout during suspend, as scsi device was stuck in _synchronize_rcu_expedited(). schedule() synchronize_rcu_expedited() synchronize_rcu() scsi_device_quiesce() scsi_bus_suspend() dpm_run_callback() __device_suspend() Fix this by using the correct exp sequence number, the one which owner of the exp_mutex initiated and passed to kworker, to index the wait queue, inside rcu_exp_wait_wake(). Signed-off-by: Neeraj Upadhyay --- Changes since v1: - Updates the commit log with failure information. kernel/rcu/tree_exp.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h index e4b77d3..28979d3 100644 --- a/kernel/rcu/tree_exp.h +++ b/kernel/rcu/tree_exp.h @@ -557,7 +557,7 @@ static void rcu_exp_wait_wake(unsigned long s) spin_unlock(&rnp->exp_lock); } smp_mb(); /* All above changes before wakeup. */ - wake_up_all(&rnp->exp_wq[rcu_seq_ctr(rcu_state.expedited_sequence) & 0x3]); + wake_up_all(&rnp->exp_wq[rcu_seq_ctr(s) & 0x3]); } trace_rcu_exp_grace_period(rcu_state.name, s, TPS("endwake")); mutex_unlock(&rcu_state.exp_wake_mutex); -- QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, hosted by The Linux Foundation