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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 601E8C001DE for ; Thu, 3 Aug 2023 01:46:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230143AbjHCBqZ (ORCPT ); Wed, 2 Aug 2023 21:46:25 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59564 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230024AbjHCBqO (ORCPT ); Wed, 2 Aug 2023 21:46:14 -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 DB4763C3A for ; Wed, 2 Aug 2023 18:45:02 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1691027102; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=aAsnqIzhgN70MVogLZRUKBp2r2KU3xDPwLa0t6GESpc=; b=jT4gYvap2Tes1KJ16NGrQonjuq8BEmfORkux3HbaYkhvItDdq0gD14b9jj4K/lif0IY3D4 Jtp59X7NVptY1iu52q8eVbUiQ5A5uqZ4YzNRDv/TzuPSVDAvSNcJbiqO0L1WmZkhpAH6em /Y627njZkuDgbpTysBfmf05+XvExYvo= 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-665-DPmLIw6sOKKoVy9VbKbCMw-1; Wed, 02 Aug 2023 21:44:59 -0400 X-MC-Unique: DPmLIw6sOKKoVy9VbKbCMw-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 AD12780027F; Thu, 3 Aug 2023 01:44:58 +0000 (UTC) Received: from [10.22.18.41] (unknown [10.22.18.41]) by smtp.corp.redhat.com (Postfix) with ESMTP id 61010200B41D; Thu, 3 Aug 2023 01:44:58 +0000 (UTC) Message-ID: <3e6a9ca3-3be5-8207-4923-8ecd141c04eb@redhat.com> Date: Wed, 2 Aug 2023 21:44:58 -0400 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.7.1 Subject: Re: [PATCH v3] perf/arm-dmc620: Fix dmc620_pmu_irqs_lock/cpu_hotplug_lock circular lock dependency Content-Language: en-US From: Waiman Long To: Will Deacon Cc: Mark Rutland , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Robin Murphy References: <20230722031729.3913953-1-longman@redhat.com> <20230728150614.GF21718@willie-the-truck> <62d4b353-0237-9ec6-a63e-8a7a6764aba5@redhat.com> In-Reply-To: <62d4b353-0237-9ec6-a63e-8a7a6764aba5@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.4 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/2/23 21:37, Waiman Long wrote: > > On 7/28/23 11:06, Will Deacon wrote: >> On Fri, Jul 21, 2023 at 11:17:28PM -0400, Waiman Long wrote: >>> 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; >>>   }; >>>     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; >>>   -    list_for_each_entry(irq, &dmc620_pmu_irqs, irqs_node) >>> -        if (irq->irq_num == irq_num && >>> refcount_inc_not_zero(&irq->refcount)) >>> +    list_for_each_entry(irq, &dmc620_pmu_irqs, irqs_node) { >>> +        if (irq->irq_num != irq_num) >>> +            continue; >>> +        if (!irq->valid) >>> +            return ERR_PTR(-EAGAIN);    /* Try again later */ >> It looks like this can bubble up to the probe() routine. Does the driver >> core handle -EAGAIN coming back from a probe routine? > Right, I should add code to handle this error condition. I think it > can be handled in dmc620_pmu_get_irq(). The important thing is to > release the mutex, wait a few ms and try again. What do you think? >> >>> +        if (refcount_inc_not_zero(&irq->refcount)) >>>               return irq; >>> +    } >>>         irq = kzalloc(sizeof(*irq), GFP_KERNEL); >>>       if (!irq) >>> @@ -447,13 +453,23 @@ static struct dmc620_pmu_irq >>> *__dmc620_pmu_get_irq(int irq_num) >>>       if (ret) >>>           goto out_free_irq; >>>   -    ret = cpuhp_state_add_instance_nocalls(cpuhp_state_num, >>> &irq->node); >>> -    if (ret) >>> -        goto out_free_irq; >>> - >>>       irq->irq_num = irq_num; >>>       list_add(&irq->irqs_node, &dmc620_pmu_irqs); >>>   +    /* >>> +     * Release dmc620_pmu_irqs_lock before calling >>> +     * cpuhp_state_add_instance_nocalls() and reacquire it afterward. >>> +     */ >>> +    mutex_unlock(&dmc620_pmu_irqs_lock); >>> +    ret = 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 = true; >> Do you actually need a new flag here, or could we use a refcount of zero >> to indicate that the irq descriptor is still being constructed? > > A refcount of zero can also mean that an existing irq is about to be > removed. Right? So I don't think we can use that for this purpose. > Besides, there is a 4-byte hole in the structure anyway for arm64. Alternatively, I can use a special reference count value, say -1, to signal that the irq is not valid yet. What do you think? Cheers, Longman