From nobody Fri Sep 12 05:39:16 2025 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id B584CC001B0 for ; Thu, 10 Aug 2023 02:17:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231527AbjHJCRq (ORCPT ); Wed, 9 Aug 2023 22:17:46 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59830 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229503AbjHJCRo (ORCPT ); Wed, 9 Aug 2023 22:17:44 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4D98C1736 for ; Wed, 9 Aug 2023 19:16:58 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1691633817; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=Kn2gdSjEHu02/v4mAeMAEf4LvFeRTaYDVdUmz7aC8GI=; b=hK0mcXyoL2OKvwJ1/aMFSy+yC91sTk7p3LRhRexxMTcXWUc/jPhtYobM/eh1u56Yf28MVh 0wY0Zsb4f/vWRI7JnlFxa3NndMBvklHEFgP4RtNgdE7sJlFDpteBimH6Rlv0yMbdwsyVHm CDcBUIejsZ4bQ9+GB0aXSk3CrH/qbRI= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-517-_Ag9I_rmMV2p-eVMLrwEjg-1; Wed, 09 Aug 2023 22:16:55 -0400 X-MC-Unique: _Ag9I_rmMV2p-eVMLrwEjg-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 5B43E185A78B; Thu, 10 Aug 2023 02:16:55 +0000 (UTC) Received: from localhost (unknown [10.72.120.5]) by smtp.corp.redhat.com (Postfix) with ESMTP id 800CE1121314; Thu, 10 Aug 2023 02:16:54 +0000 (UTC) From: Ming Lei To: Thomas Gleixner Cc: linux-kernel@vger.kernel.org, Ming Lei , Keith Busch , linux-nvme@lists.infradead.org, linux-block@lists.infradead.org, Yi Zhang , Guangwu Zhang Subject: [PATCH] lib/group_cpus.c: avoid to acquire cpu hotplug lock in group_cpus_evenly Date: Thu, 10 Aug 2023 10:16:40 +0800 Message-Id: <20230810021640.252033-1-ming.lei@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.1 on 10.11.54.3 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" group_cpus_evenly() could be part of storage driver's error handler, such as nvme driver, when may happen during CPU hotplug, in which storage queue has to drain its pending IOs because all CPUs associated with the queue are offline and the queue is becoming inactive. And handling IO needs error handler to provide forward progress. Then dead lock is caused: 1) inside CPU hotplug handler, CPU hotplug lock is held, and blk-mq's handler is waiting for inflight IO 2) error handler is waiting for CPU hotplug lock 3) inflight IO can't be completed in blk-mq's CPU hotplug handler because error handling can't provide forward progress. Solve the deadlock by not holding CPU hotplug lock in group_cpus_evenly(), in which two stage spreads are taken: 1) the 1st stage is over all present CPUs; 2) the end stage is over all other CPUs. Turns out the two stage spread just needs consistent 'cpu_present_mask', and remove the CPU hotplug lock by storing it into one local cache. This way doesn't change correctness, because all CPUs are still covered. Cc: Keith Busch Cc: linux-nvme@lists.infradead.org Cc: linux-block@lists.infradead.org Reported-by: Yi Zhang Reported-by: Guangwu Zhang Signed-off-by: Ming Lei Tested-by: Guangwu Zhang --- lib/group_cpus.c | 22 ++++++++++++++++------ 1 file changed, 16 insertions(+), 6 deletions(-) diff --git a/lib/group_cpus.c b/lib/group_cpus.c index aa3f6815bb12..15006e79196f 100644 --- a/lib/group_cpus.c +++ b/lib/group_cpus.c @@ -348,6 +348,7 @@ struct cpumask *group_cpus_evenly(unsigned int numgrps) { unsigned int curgrp =3D 0, nr_present =3D 0, nr_others =3D 0; cpumask_var_t *node_to_cpumask; + cpumask_var_t local_cpu_present_mask; cpumask_var_t nmsk, npresmsk; int ret =3D -ENOMEM; struct cpumask *masks =3D NULL; @@ -355,6 +356,16 @@ struct cpumask *group_cpus_evenly(unsigned int numgrps) if (!zalloc_cpumask_var(&nmsk, GFP_KERNEL)) return NULL; =20 + if (!zalloc_cpumask_var(&local_cpu_present_mask, GFP_KERNEL)) + goto fail_local_pres_mask; + + /* + * Make a local cache of 'cpu_present_mask', so the two stages + * spread can observe consistent 'cpu_present_mask' without holding + * cpu hotplug lock. + */ + cpumask_copy(local_cpu_present_mask, cpu_present_mask); + if (!zalloc_cpumask_var(&npresmsk, GFP_KERNEL)) goto fail_nmsk; =20 @@ -366,13 +377,11 @@ struct cpumask *group_cpus_evenly(unsigned int numgrp= s) if (!masks) goto fail_node_to_cpumask; =20 - /* Stabilize the cpumasks */ - cpus_read_lock(); build_node_to_cpumask(node_to_cpumask); =20 /* grouping present CPUs first */ ret =3D __group_cpus_evenly(curgrp, numgrps, node_to_cpumask, - cpu_present_mask, nmsk, masks); + local_cpu_present_mask, nmsk, masks); if (ret < 0) goto fail_build_affinity; nr_present =3D ret; @@ -387,15 +396,13 @@ struct cpumask *group_cpus_evenly(unsigned int numgrp= s) curgrp =3D 0; else curgrp =3D nr_present; - cpumask_andnot(npresmsk, cpu_possible_mask, cpu_present_mask); + cpumask_andnot(npresmsk, cpu_possible_mask, local_cpu_present_mask); ret =3D __group_cpus_evenly(curgrp, numgrps, node_to_cpumask, npresmsk, nmsk, masks); if (ret >=3D 0) nr_others =3D ret; =20 fail_build_affinity: - cpus_read_unlock(); - if (ret >=3D 0) WARN_ON(nr_present + nr_others < numgrps); =20 @@ -406,6 +413,9 @@ struct cpumask *group_cpus_evenly(unsigned int numgrps) free_cpumask_var(npresmsk); =20 fail_nmsk: + free_cpumask_var(local_cpu_present_mask); + + fail_local_pres_mask: free_cpumask_var(nmsk); if (ret < 0) { kfree(masks); --=20 2.40.1