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 31824C0015E for ; Fri, 28 Jul 2023 15:06:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236589AbjG1PGY (ORCPT ); Fri, 28 Jul 2023 11:06:24 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43050 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233791AbjG1PGV (ORCPT ); Fri, 28 Jul 2023 11:06:21 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C432035B6 for ; Fri, 28 Jul 2023 08:06:20 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 4968762174 for ; Fri, 28 Jul 2023 15:06:20 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7DD53C433C7; Fri, 28 Jul 2023 15:06:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1690556779; bh=7y4hzP6vJqpTva+r7AnqXZl9OPsfZosUFbaU/iF84wQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=up0kGsazxmcXACUeeQ0xvZ2ONzNolMwL9h5yhFkW182xcIvXqOsD48bofL6ms4M3Q UuWRJnWet7vLEsGegXBdkijgxbbNULqDeT4UsIQiAQyVz6nVedGn6TNEzF/4F6LJWU gd1xai53OGXBZI3Ts5og8VPD+S3QhTzIQZj4GeFBttRzlMlRSLsTK08szF/M5rsOwL Ecl053XYShAasJmSObTlpPy2B5h6XBlPE7rm2n6uJSqCWvh0JW44WK2KynNDGYRZPU uwkW7Bl3qTBXrFN9D8IZwmMuyIlMfTBJqInoAh2MtuSfgAGjP72PPt0QcPRa8LfDgO eBpR7Jv8Aewcg== Date: Fri, 28 Jul 2023 16:06:14 +0100 From: Will Deacon To: Waiman Long Cc: Mark Rutland , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Robin Murphy Subject: Re: [PATCH v3] perf/arm-dmc620: Fix dmc620_pmu_irqs_lock/cpu_hotplug_lock circular lock dependency Message-ID: <20230728150614.GF21718@willie-the-truck> References: <20230722031729.3913953-1-longman@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230722031729.3913953-1-longman@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? > + 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? Will