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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 0E546C001DE for ; Fri, 28 Jul 2023 15:06:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=EbZI59oLQJzegp2kca4qJGz63yq8GeclblYIIlaAMmg=; b=VHtq8uUbtZDLc1 QTWTKMzUM31ru2DlBMk82mHiHIbEgg+LgBBjonzUdHd9GdH+S8xMfZMGGPFW2dZjuLnxqr3sVKKGT cmOkAheI2YXmjzG0HNrekMV7TOw1hx3scRkEni8TorteK3Y1JGwl+86nh+/glibSdxsYBa7yb12/Q EfYE9LJO7CQMX6WnBAsf+Hau2n02E0EoTa/75ulYohmJUIbWTCA2Bhoahw06EyJFBGQArj2lChAS4 gF97OBCmvpyur5DlUeWRZbwTnWqOq1Tverp34gMa25S7Cz7pTGr+74gMAlnEBPCQmqeJ7yNZUQp8s cNQut5QjA9THubN59Bkw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1qPP2u-003mYF-1P; Fri, 28 Jul 2023 15:06:24 +0000 Received: from dfw.source.kernel.org ([2604:1380:4641:c500::1]) by bombadil.infradead.org with esmtps (Exim 4.96 #2 (Red Hat Linux)) id 1qPP2r-003mXV-2a for linux-arm-kernel@lists.infradead.org; Fri, 28 Jul 2023 15:06:23 +0000 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 480C562169; 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-Disposition: inline In-Reply-To: <20230722031729.3913953-1-longman@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230728_080621_935288_CB43C2BC X-CRM114-Status: GOOD ( 30.25 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.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 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel