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Mon, 30 Mar 2026 22:11:31 +0000 From: Aaron Tomlin To: axboe@kernel.dk, kbusch@kernel.org, hch@lst.de, sagi@grimberg.me, mst@redhat.com Cc: atomlin@atomlin.com, aacraid@microsemi.com, James.Bottomley@HansenPartnership.com, martin.petersen@oracle.com, liyihang9@h-partners.com, kashyap.desai@broadcom.com, sumit.saxena@broadcom.com, shivasharan.srikanteshwara@broadcom.com, chandrakanth.patil@broadcom.com, sathya.prakash@broadcom.com, sreekanth.reddy@broadcom.com, suganath-prabu.subramani@broadcom.com, ranjan.kumar@broadcom.com, jinpu.wang@cloud.ionos.com, tglx@kernel.org, mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, akpm@linux-foundation.org, maz@kernel.org, ruanjinjie@huawei.com, bigeasy@linutronix.de, yphbchou0911@gmail.com, wagi@kernel.org, frederic@kernel.org, longman@redhat.com, chenridong@huawei.com, hare@suse.de, kch@nvidia.com, ming.lei@redhat.com, steve@abita.co, sean@ashe.io, chjohnst@gmail.com, neelx@suse.com, mproche@gmail.com, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux.dev, linux-nvme@lists.infradead.org, linux-scsi@vger.kernel.org, megaraidlinux.pdl@broadcom.com, mpi3mr-linuxdrv.pdl@broadcom.com, MPT-FusionLinux.pdl@broadcom.com Subject: [PATCH v9 11/13] blk-mq: prevent offlining hk CPUs with associated online isolated CPUs Date: Mon, 30 Mar 2026 18:10:45 -0400 Message-ID: <20260330221047.630206-12-atomlin@atomlin.com> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20260330221047.630206-1-atomlin@atomlin.com> References: <20260330221047.630206-1-atomlin@atomlin.com> Content-Transfer-Encoding: quoted-printable X-ClientProxiedBy: BN1PR12CA0023.namprd12.prod.outlook.com (2603:10b6:408:e1::28) To CWLP123MB3523.GBRP123.PROD.OUTLOOK.COM (2603:10a6:400:70::10) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CWLP123MB3523:EE_|CWLP123MB3841:EE_ X-MS-Office365-Filtering-Correlation-Id: 944e7599-648b-451b-f31c-08de8ea94c01 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|7416014|366016|1800799024|56012099003|22082099003|18002099003; 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charset="utf-8" From: Daniel Wagner When isolcpus=3Dio_queue is enabled, and the last housekeeping CPU for a given hctx goes offline, there would be no CPU left to handle I/O. To prevent I/O stalls, prevent offlining housekeeping CPUs that are still serving isolated CPUs. When isolcpus=3Dio_queue is enabled and the last housekeeping CPU for a given hctx goes offline, no CPU would be left to handle I/O. To prevent I/O stalls, disallow offlining housekeeping CPUs that are still serving isolated CPUs. Reviewed-by: Aaron Tomlin Reviewed-by: Hannes Reinecke Signed-off-by: Daniel Wagner --- block/blk-mq.c | 42 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 42 insertions(+) diff --git a/block/blk-mq.c b/block/blk-mq.c index 3da2215b2912..8671f2170880 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -3699,6 +3699,43 @@ static bool blk_mq_hctx_has_requests(struct blk_mq_h= w_ctx *hctx) return data.has_rq; } =20 +static bool blk_mq_hctx_can_offline_hk_cpu(struct blk_mq_hw_ctx *hctx, + unsigned int this_cpu) +{ + const struct cpumask *hk_mask =3D housekeeping_cpumask(HK_TYPE_IO_QUEUE); + + for (int i =3D 0; i < hctx->nr_ctx; i++) { + struct blk_mq_ctx *ctx =3D hctx->ctxs[i]; + + if (ctx->cpu =3D=3D this_cpu) + continue; + + /* + * Check if this context has at least one online + * housekeeping CPU; in this case the hardware context is + * usable. + */ + if (cpumask_test_cpu(ctx->cpu, hk_mask) && + cpu_online(ctx->cpu)) + break; + + /* + * The context doesn't have any online housekeeping CPUs, + * but there might be an online isolated CPU mapped to + * it. + */ + if (cpu_is_offline(ctx->cpu)) + continue; + + pr_warn("%s: trying to offline hctx%d but there is still an online isolc= pu CPU %d mapped to it\n", + hctx->queue->disk->disk_name, + hctx->queue_num, ctx->cpu); + return false; + } + + return true; +} + static bool blk_mq_hctx_has_online_cpu(struct blk_mq_hw_ctx *hctx, unsigned int this_cpu) { @@ -3731,6 +3768,11 @@ static int blk_mq_hctx_notify_offline(unsigned int c= pu, struct hlist_node *node) struct blk_mq_hw_ctx, cpuhp_online); int ret =3D 0; =20 + if (housekeeping_enabled(HK_TYPE_IO_QUEUE)) { + if (!blk_mq_hctx_can_offline_hk_cpu(hctx, cpu)) + return -EINVAL; + } + if (!hctx->nr_ctx || blk_mq_hctx_has_online_cpu(hctx, cpu)) return 0; =20 --=20 2.51.0