From nobody Thu Dec 18 14:25:05 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 DBEE0C71134 for ; Fri, 18 Aug 2023 01:54:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1357129AbjHRBxu (ORCPT ); Thu, 17 Aug 2023 21:53:50 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49538 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1357118AbjHRBxp (ORCPT ); Thu, 17 Aug 2023 21:53:45 -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 B0AA8100 for ; Thu, 17 Aug 2023 18:52:58 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1692323577; 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=f42bCxvlAvmcujooXy3bffnAnWJZzzFDZ6+tYkOrJJ0=; b=G2YLFqK08cqk+wIqS5Xf2DijFHoO48ntM7J1OGSiMteSdr7RYYIQT8XURfQww92LFBGuJl Ep/c46ajkCuavgvXY6AeTrQtiZdmelguZHQkBIofhxgvjS+ubUsPkONBQ41OrIUkmmL56J WgSFQWZLwCVSrARCKnVrrNW5WO6U3So= Received: from mimecast-mx02.redhat.com (66.187.233.73 [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-681-tyZm7me1N8SlX0ks18qw8Q-1; Thu, 17 Aug 2023 21:52:54 -0400 X-MC-Unique: tyZm7me1N8SlX0ks18qw8Q-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 1CD8E3C01C1B; Fri, 18 Aug 2023 01:52:54 +0000 (UTC) Received: from localhost (unknown [10.72.120.4]) by smtp.corp.redhat.com (Postfix) with ESMTP id 33F84C15BAD; Fri, 18 Aug 2023 01:52:52 +0000 (UTC) From: Ming Lei To: Jens Axboe , Thomas Gleixner Cc: linux-kernel@vger.kernel.org, Ming Lei , Keith Busch , linux-nvme@lists.infradead.org, linux-block@vger.kernel.org, Yi Zhang , Guangwu Zhang Subject: [PATCH V2] lib/group_cpus.c: avoid to acquire cpu hotplug lock in group_cpus_evenly Date: Fri, 18 Aug 2023 09:52:44 +0800 Message-Id: <20230818015244.1176929-1-ming.lei@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 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@vger.kernel.org Reported-by: Yi Zhang Reported-by: Guangwu Zhang Tested-by: Guangwu Zhang Signed-off-by: Ming Lei Reviewed-by: Chengming Zhou --- V2: - fix "Cc: block list" - add tested-by tag 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