From nobody Wed Dec 17 14:19:50 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 800A9C71156 for ; Fri, 18 Aug 2023 14:04:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1377593AbjHROEJ (ORCPT ); Fri, 18 Aug 2023 10:04:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38114 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1377684AbjHRODY (ORCPT ); Fri, 18 Aug 2023 10:03:24 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 90E7C422B for ; Fri, 18 Aug 2023 07:01:58 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1692367317; 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=Km5bEjvHFKHGKfuEsrUW3JzJAnKEezHhvxomlDHV3DU=; b=c3aWLpN/uon7e6QUB9ZGMUoa7ZI7Eu2VH99M2yyBADld6b5T36iIa6rGT8rMFxwK/v/enR bQLK7gp8bDYACdByhacsVbpyt8a9Ub/3DZIMeX/AewzSKD6pqO68stt8LTKO7z4vJwvqU1 DbGhN0wTBzHnjLw5v2gwt2eqiFJy678= 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-610-gY35I9gfO6u6S84jANp4JA-1; Fri, 18 Aug 2023 10:01:51 -0400 X-MC-Unique: gY35I9gfO6u6S84jANp4JA-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.rdu2.redhat.com [10.11.54.7]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 0621A85CBE2; Fri, 18 Aug 2023 14:01:51 +0000 (UTC) Received: from localhost (unknown [10.72.120.3]) by smtp.corp.redhat.com (Postfix) with ESMTP id C787E140E96E; Fri, 18 Aug 2023 14:01:49 +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 , Chengming Zhou Subject: [PATCH V3] lib/group_cpus.c: avoid to acquire cpu hotplug lock in group_cpus_evenly Date: Fri, 18 Aug 2023 22:01:45 +0800 Message-Id: <20230818140145.1229805-1-ming.lei@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.1 on 10.11.54.7 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 Reviewed-by: Chengming Zhou Signed-off-by: Ming Lei --- V3: - reuse `npresmsk`, and avoid to allocate new variable, suggested by Chengming Zhou V2: - fix "Cc: block list" - add tested-by tag lib/group_cpus.c | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-) diff --git a/lib/group_cpus.c b/lib/group_cpus.c index aa3f6815bb12..fffe8a893597 100644 --- a/lib/group_cpus.c +++ b/lib/group_cpus.c @@ -366,13 +366,18 @@ 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 + /* + * 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(npresmsk, cpu_present_mask); + /* grouping present CPUs first */ ret =3D __group_cpus_evenly(curgrp, numgrps, node_to_cpumask, - cpu_present_mask, nmsk, masks); + npresmsk, nmsk, masks); if (ret < 0) goto fail_build_affinity; nr_present =3D ret; @@ -387,15 +392,13 @@ 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, npresmsk); 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 --=20 2.40.1