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=-9.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,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 A02C2C43141 for ; Fri, 15 Nov 2019 17:28:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7A0AD2073B for ; Fri, 15 Nov 2019 17:28:30 +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="Z0MqtVeP"; dkim=fail reason="key not found in DNS" (0-bit key) header.d=codeaurora.org header.i=@codeaurora.org header.b="HDl9BTrw" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727629AbfKOR23 (ORCPT ); Fri, 15 Nov 2019 12:28:29 -0500 Received: from smtp.codeaurora.org ([198.145.29.96]:35704 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727543AbfKOR23 (ORCPT ); Fri, 15 Nov 2019 12:28:29 -0500 Received: by smtp.codeaurora.org (Postfix, from userid 1000) id 4F5E260C5F; Fri, 15 Nov 2019 17:28:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=codeaurora.org; s=default; t=1573838908; bh=GYmPEXvxT/OZTdh5b9aiAB0ZpYeDWC04SZk0qHLp/Mw=; h=From:To:Cc:Subject:Date:From; b=Z0MqtVeP25YA3RWwYJuXDiDOJaL9g/YVjgZeNP2fdXgA6VLvKcQl7pVYDck5gp4M9 1Bdp3CxRFGZLc66NaM+LKvQLEoJeGg0olhCjwpCVLt5vr9RY6VYO5DSCft4piSRMcG 4QOn9MPfygh5mjf/co0cULH15h1n4bsIVTxP0mko= Received: from neeraju-linux.qualcomm.com (blr-c-bdr-fw-01_globalnat_allzones-outside.qualcomm.com [103.229.19.19]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-SHA256 (128/128 bits)) (No client certificate requested) (Authenticated sender: neeraju@smtp.codeaurora.org) by smtp.codeaurora.org (Postfix) with ESMTPSA id 454D560C5F; Fri, 15 Nov 2019 17:28:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=codeaurora.org; s=default; t=1573838907; bh=GYmPEXvxT/OZTdh5b9aiAB0ZpYeDWC04SZk0qHLp/Mw=; h=From:To:Cc:Subject:Date:From; b=HDl9BTrwU0aaxOsxtqXaV9gYmuXQmv3mMqX2L3UMwzhRmVOCeOYM8JkiULr30s1s2 Ij23qONg3YLc1gwUi7eHut+tny0850fcR6Zq9MPmsL/fyatmbZ9uxKKnF5GANMG8ol jXfMxBxnKM6ktm8ImHdqLhMK15e+J4FAMsQS+jCg= DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org 454D560C5F Authentication-Results: pdx-caf-mail.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: pdx-caf-mail.web.codeaurora.org; spf=none smtp.mailfrom=neeraju@codeaurora.org From: Neeraj Upadhyay To: paulmck@linux.vnet.ibm.com, josh@joshtriplett.org, joel@joelfernandes.org, rostedt@goodmis.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com Cc: linux-kernel@vger.kernel.org, rcu@vger.kernel.org, pkondeti@codeaurora.org, prsood@codeaurora.org, gkohli@codeaurora.org, Neeraj Upadhyay Subject: [PATCH] rcu: Fix missed wakeup of exp_wq waiters Date: Fri, 15 Nov 2019 22:58:14 +0530 Message-Id: <1573838894-23027-1-git-send-email-neeraju@codeaurora.org> X-Mailer: git-send-email 1.9.1 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@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(). _synchronize_rcu_expedited() s = 0b'100 exp_funnel_lock() wait_event(rnp->exp_wq[rcu_seq_ctr(s) & 0x3] 2. The Exp GP 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. rcu_exp_wait_wake() rcu_exp_wait_wake() rcu_exp_gp_seq_end(rsp) // rsp->expedited_sequence is incremented // to 0b'100' 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. As kworker A 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]); Fix this by using the correct sequence number for wake_up_all() inside rcu_exp_wait_wake(). Signed-off-by: Neeraj Upadhyay --- 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