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 A6A54C001DE for ; Fri, 18 Aug 2023 06:59:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=CmMGnP7L7bn/5ssBCNCkB8ryZejZU4L6IU8tNWtA8SU=; b=xlArx0pIxGGNAU+ENSJX7wAiZ5 Q1ebJrS07mpuozfdhWYjP+lYKK2b1SMD2ax30Yp2XyBVbMzbiTiBw6yQK2bW29cC5YuLCez90U1eQ Gy5lh7rCXrom3OFJ2VOQAXwfAu/5NCLOIZbbLwoyInxmb8S96eyoHor/YsNd9tJPGK7/4WC1Kfg0B OyKF/X7jy2Bs7zsQNxPU/tFXs0bJLTd5hDgZPhAJhj2xIt96NKS5LbqWRT/Tb7CKTRv8wZECVi/B0 eUqOZMhwntaZcLZ6twFJibwPBUCeNGfmZjwV70bWdI1/RS4gWwF/6ihcrrluGI7GbmkiU0NBi8eKd W6zrL5fg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1qWtSJ-007q1N-2r; Fri, 18 Aug 2023 06:59:35 +0000 Received: from out-15.mta0.migadu.com ([91.218.175.15]) by bombadil.infradead.org with esmtps (Exim 4.96 #2 (Red Hat Linux)) id 1qWtSF-007q0K-2L for linux-nvme@lists.infradead.org; Fri, 18 Aug 2023 06:59:34 +0000 Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1692341959; 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=CmMGnP7L7bn/5ssBCNCkB8ryZejZU4L6IU8tNWtA8SU=; b=qk7w6tviAs5Oa5HG9F4Y1FXDH7P1BeQVk9ddJEzlTyeN+JDa1EwWL6exFVAaxqWOeEyiL3 GJ+u9sm8V8Dpgi/mdD8dxbYG7FJgVJ/zF4fKPIUM6n3WcMmO5IRODTQA5Djyp4EDiw4VCq V+e5XLxhAaI+92zrhup++X+05QLElEM= Date: Fri, 18 Aug 2023 14:59:13 +0800 MIME-Version: 1.0 Subject: Re: [PATCH V2] lib/group_cpus.c: avoid to acquire cpu hotplug lock in group_cpus_evenly Content-Language: en-US To: Ming Lei , Jens Axboe , Thomas Gleixner Cc: linux-kernel@vger.kernel.org, Keith Busch , linux-nvme@lists.infradead.org, linux-block@vger.kernel.org, Yi Zhang , Guangwu Zhang References: <20230818015244.1176929-1-ming.lei@redhat.com> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Chengming Zhou In-Reply-To: <20230818015244.1176929-1-ming.lei@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230817_235932_375602_EE5D8F69 X-CRM114-Status: GOOD ( 24.24 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org Hi, On 2023/8/18 09:52, Ming Lei wrote: > 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 > Signed-off-by: Ming Lei > --- > V2: > - fix "Cc: block list" > - add tested-by tag > > lib/group_cpus.c | 22 ++++++++++++++++------ > 1 file changed, 16 insertions(+), 6 deletions(-) > > diff --git a/lib/group_cpus.c b/lib/group_cpus.c > index aa3f6815bb12..15006e79196f 100644 > --- a/lib/group_cpus.c > +++ b/lib/group_cpus.c > @@ -348,6 +348,7 @@ struct cpumask *group_cpus_evenly(unsigned int numgrps) > { > unsigned int curgrp = 0, nr_present = 0, nr_others = 0; > cpumask_var_t *node_to_cpumask; > + cpumask_var_t local_cpu_present_mask; > cpumask_var_t nmsk, npresmsk; > int ret = -ENOMEM; > struct cpumask *masks = NULL; > @@ -355,6 +356,16 @@ struct cpumask *group_cpus_evenly(unsigned int numgrps) > if (!zalloc_cpumask_var(&nmsk, GFP_KERNEL)) > return NULL; > > + if (!zalloc_cpumask_var(&local_cpu_present_mask, GFP_KERNEL)) > + goto fail_local_pres_mask; > + > + /* > + * 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(local_cpu_present_mask, cpu_present_mask); > + Maybe we can reuse npresmsk instead of allocating another cpumask? In the first stage: npresmsk = cpu_present_mask In the second stage: npresmsk = cpu_possible_mask & ~npresmsk > if (!zalloc_cpumask_var(&npresmsk, GFP_KERNEL)) > goto fail_nmsk; > > @@ -366,13 +377,11 @@ struct cpumask *group_cpus_evenly(unsigned int numgrps) > if (!masks) > goto fail_node_to_cpumask; > > - /* Stabilize the cpumasks */ > - cpus_read_lock(); > build_node_to_cpumask(node_to_cpumask); > > /* grouping present CPUs first */ > ret = __group_cpus_evenly(curgrp, numgrps, node_to_cpumask, > - cpu_present_mask, nmsk, masks); > + local_cpu_present_mask, nmsk, masks); > if (ret < 0) > goto fail_build_affinity; > nr_present = ret; > @@ -387,15 +396,13 @@ struct cpumask *group_cpus_evenly(unsigned int numgrps) > curgrp = 0; > else > curgrp = nr_present; > - cpumask_andnot(npresmsk, cpu_possible_mask, cpu_present_mask); > + cpumask_andnot(npresmsk, cpu_possible_mask, local_cpu_present_mask); > ret = __group_cpus_evenly(curgrp, numgrps, node_to_cpumask, > npresmsk, nmsk, masks); > if (ret >= 0) > nr_others = ret; > > fail_build_affinity: > - cpus_read_unlock(); > - > if (ret >= 0) > WARN_ON(nr_present + nr_others < numgrps); This fail_build_affinity tag seems unneeded anymore. The patch looks good to me: Reviewed-by: Chengming Zhou Thanks. > > @@ -406,6 +413,9 @@ struct cpumask *group_cpus_evenly(unsigned int numgrps) > free_cpumask_var(npresmsk); > > fail_nmsk: > + free_cpumask_var(local_cpu_present_mask); > + > + fail_local_pres_mask: > free_cpumask_var(nmsk); > if (ret < 0) { > kfree(masks);