From nobody Sat Feb 7 17:09:49 2026 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 11DEFEB64DA for ; Sat, 22 Jul 2023 03:18:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230085AbjGVDSe (ORCPT ); Fri, 21 Jul 2023 23:18:34 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39944 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229503AbjGVDSa (ORCPT ); Fri, 21 Jul 2023 23:18:30 -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 252F03A9C for ; Fri, 21 Jul 2023 20:17:43 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1689995863; 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=0uW4VHgKV+Lqk0wGj2Kld/LW6LChZPKDcy+khsmFX/c=; b=TTbdomkbmAGMuYeSn12K2JvROlXP9ZDFJC20jC3OuHLL9OqDMwj1L2veume5WiT/BgrIDM WBclYLnq09QcrOYnX7mcpapCVaUPdYEJ+1VXMSmhhjwUoc8s1CMCBCzzozX/c/Z8BUfP5O mbLo6sqNRy9BCYItYYQ7KsVN8NN3k+o= 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-625-ds7PrvWIO_iOLDwToedKAA-1; Fri, 21 Jul 2023 23:17:40 -0400 X-MC-Unique: ds7PrvWIO_iOLDwToedKAA-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 24EBE3C0D183; Sat, 22 Jul 2023 03:17:40 +0000 (UTC) Received: from llong.com (unknown [10.22.16.21]) by smtp.corp.redhat.com (Postfix) with ESMTP id AEE77200A7CA; Sat, 22 Jul 2023 03:17:39 +0000 (UTC) From: Waiman Long To: Will Deacon , Mark Rutland Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Robin Murphy , Waiman Long Subject: [PATCH v3] perf/arm-dmc620: Fix dmc620_pmu_irqs_lock/cpu_hotplug_lock circular lock dependency Date: Fri, 21 Jul 2023 23:17:28 -0400 Message-Id: <20230722031729.3913953-1-longman@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.1 on 10.11.54.4 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" The following circular locking dependency was reported when running cpus online/offline test on an arm64 system. [ 84.195923] Chain exists of: dmc620_pmu_irqs_lock --> cpu_hotplug_lock --> cpuhp_state-= down [ 84.207305] Possible unsafe locking scenario: [ 84.213212] CPU0 CPU1 [ 84.217729] ---- ---- [ 84.222247] lock(cpuhp_state-down); [ 84.225899] lock(cpu_hotplug_lock); [ 84.232068] lock(cpuhp_state-down); [ 84.238237] lock(dmc620_pmu_irqs_lock); [ 84.242236] *** DEADLOCK *** The problematic locking order seems to be lock(dmc620_pmu_irqs_lock) --> lock(cpu_hotplug_lock) This locking order happens when dmc620_pmu_get_irq() is called from dmc620_pmu_device_probe(). Since dmc620_pmu_irqs_lock is used for protecting the dmc620_pmu_irqs structure only, we don't actually need to hold the lock when adding a new instance to the CPU hotplug subsystem. Fix this possible deadlock scenario by releasing the lock before calling cpuhp_state_add_instance_nocalls() and reacquiring it afterward. To avoid the possibility of 2 racing dmc620_pmu_get_irq() calls inserting duplicated dmc620_pmu_irq structures with the same irq number, a dummy entry is inserted before releasing the lock which will block a competing thread from inserting another irq structure of the same irq number. Suggested-by: Robin Murphy Signed-off-by: Waiman Long --- drivers/perf/arm_dmc620_pmu.c | 28 ++++++++++++++++++++++------ 1 file changed, 22 insertions(+), 6 deletions(-) diff --git a/drivers/perf/arm_dmc620_pmu.c b/drivers/perf/arm_dmc620_pmu.c index 9d0f01c4455a..7cafd4dd4522 100644 --- a/drivers/perf/arm_dmc620_pmu.c +++ b/drivers/perf/arm_dmc620_pmu.c @@ -76,6 +76,7 @@ struct dmc620_pmu_irq { refcount_t refcount; unsigned int irq_num; unsigned int cpu; + unsigned int valid; }; =20 struct dmc620_pmu { @@ -423,9 +424,14 @@ static struct dmc620_pmu_irq *__dmc620_pmu_get_irq(int= irq_num) struct dmc620_pmu_irq *irq; int ret; =20 - list_for_each_entry(irq, &dmc620_pmu_irqs, irqs_node) - if (irq->irq_num =3D=3D irq_num && refcount_inc_not_zero(&irq->refcount)) + list_for_each_entry(irq, &dmc620_pmu_irqs, irqs_node) { + if (irq->irq_num !=3D irq_num) + continue; + if (!irq->valid) + return ERR_PTR(-EAGAIN); /* Try again later */ + if (refcount_inc_not_zero(&irq->refcount)) return irq; + } =20 irq =3D kzalloc(sizeof(*irq), GFP_KERNEL); if (!irq) @@ -447,13 +453,23 @@ static struct dmc620_pmu_irq *__dmc620_pmu_get_irq(in= t irq_num) if (ret) goto out_free_irq; =20 - ret =3D cpuhp_state_add_instance_nocalls(cpuhp_state_num, &irq->node); - if (ret) - goto out_free_irq; - irq->irq_num =3D irq_num; list_add(&irq->irqs_node, &dmc620_pmu_irqs); =20 + /* + * Release dmc620_pmu_irqs_lock before calling + * cpuhp_state_add_instance_nocalls() and reacquire it afterward. + */ + mutex_unlock(&dmc620_pmu_irqs_lock); + ret =3D cpuhp_state_add_instance_nocalls(cpuhp_state_num, &irq->node); + mutex_lock(&dmc620_pmu_irqs_lock); + + if (ret) { + list_del(&irq->irqs_node); + goto out_free_irq; + } + + irq->valid =3D true; return irq; =20 out_free_irq: --=20 2.31.1