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Wed, 13 May 2026 00:55:31 +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, tom.leiming@gmail.com, steve@abita.co, sean@ashe.io, chjohnst@gmail.com, neelx@suse.com, mproche@gmail.com, nick.lange@gmail.com, marco.crivellari@suse.com, rishil1999@outlook.com, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v13 5/8] blk-mq: use hk cpus only when isolcpus=io_queue is enabled Date: Tue, 12 May 2026 20:55:06 -0400 Message-ID: <20260513005509.135966-6-atomlin@atomlin.com> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20260513005509.135966-1-atomlin@atomlin.com> References: <20260513005509.135966-1-atomlin@atomlin.com> Content-Transfer-Encoding: 8bit Content-Type: text/plain X-ClientProxiedBy: BN9PR03CA0108.namprd03.prod.outlook.com (2603:10b6:408:fd::23) To CWLP123MB3523.GBRP123.PROD.OUTLOOK.COM (2603:10a6:400:70::10) Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CWLP123MB3523:EE_|CWLP123MB4226:EE_ X-MS-Office365-Filtering-Correlation-Id: 4e18df84-766f-4f46-65c8-08deb08a54dd X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|376014|366016|7416014|3023799003|56012099003|18002099003|22082099003; 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A hctx is only operational when there is at least one online housekeeping CPU assigned (aka active_hctx). Thus, check the final mapping that there is no hctx which has only offline housekeeing CPU and online isolated CPUs. Example mapping result: 16 online CPUs isolcpus=io_queue,2-3,6-7,12-13 Queue mapping: hctx0: default 0 2 hctx1: default 1 3 hctx2: default 4 6 hctx3: default 5 7 hctx4: default 8 12 hctx5: default 9 13 hctx6: default 10 hctx7: default 11 hctx8: default 14 hctx9: default 15 IRQ mapping: irq 42 affinity 0 effective 0 nvme0q0 irq 43 affinity 0 effective 0 nvme0q1 irq 44 affinity 1 effective 1 nvme0q2 irq 45 affinity 4 effective 4 nvme0q3 irq 46 affinity 5 effective 5 nvme0q4 irq 47 affinity 8 effective 8 nvme0q5 irq 48 affinity 9 effective 9 nvme0q6 irq 49 affinity 10 effective 10 nvme0q7 irq 50 affinity 11 effective 11 nvme0q8 irq 51 affinity 14 effective 14 nvme0q9 irq 52 affinity 15 effective 15 nvme0q10 A corner case is when the number of online CPUs and present CPUs differ and the driver asks for less queues than online CPUs, e.g. 8 online CPUs, 16 possible CPUs isolcpus=io_queue,2-3,6-7,12-13 virtio_blk.num_request_queues=2 Queue mapping: hctx0: default 0 1 2 3 4 5 6 7 8 12 13 hctx1: default 9 10 11 14 15 IRQ mapping irq 27 affinity 0 effective 0 virtio0-config irq 28 affinity 0-1,4-5,8 effective 5 virtio0-req.0 irq 29 affinity 9-11,14-15 effective 0 virtio0-req.1 Noteworthy is that for the normal/default configuration (!isoclpus) the mapping will change for systems which have non hyperthreading CPUs. The main assignment loop will completely rely that group_mask_cpus_evenly to do the right thing. The old code would distribute the CPUs linearly over the hardware context: queue mapping for /dev/nvme0n1 hctx0: default 0 8 hctx1: default 1 9 hctx2: default 2 10 hctx3: default 3 11 hctx4: default 4 12 hctx5: default 5 13 hctx6: default 6 14 hctx7: default 7 15 The assign each hardware context the map generated by the group_mask_cpus_evenly function: queue mapping for /dev/nvme0n1 hctx0: default 0 1 hctx1: default 2 3 hctx2: default 4 5 hctx3: default 6 7 hctx4: default 8 9 hctx5: default 10 11 hctx6: default 12 13 hctx7: default 14 15 In case of hyperthreading CPUs, the resulting map stays the same. Signed-off-by: Daniel Wagner [atomlin: - Updated blk_mq_validate() to use test_bit() for the new bitmap - Replaced __free cleanups with traditional goto unwinding to align with subsystem styling - Updated blk_mq_map_fallback() to use qmap->queue_offset ensuring secondary maps do not incorrectly route to the primary default map - Added a bitmap_empty() check to prevent out-of-bounds CPU routing when all mapped CPUs are offline - Migrated active_hctx to a dynamically sized bitmap to fix an out-of-bounds write when hardware queues exceed the system CPU count - Fixed absolute vs. relative hardware queue index mix-up in blk_mq_map_queues() and validation checks - Fixed typographical errors - Reduced stack frame size of blk_mq_num_queues() - Resolved a TOCTOU race against CPU hotplug events by snapshotting cpu_online_mask to ensure mapping and validation phases agree - Corrected a loop overwrite bug in blk_mq_map_queues() by iterating directly over masks to prevent orphaned queues from being activated - Restored topology-aware multi-queue fallback in blk_mq_map_hw_queues() for devices lacking IRQ affinity hints - Hardened isolation logic in blk_mq_map_hw_queues() to require online housekeeping CPUs before marking a hardware queue as active - Optimised active queue evaluations by short-circuiting redundant checks once a valid CPU is found] Signed-off-by: Aaron Tomlin --- block/blk-mq-cpumap.c | 224 ++++++++++++++++++++++++++++++++++++++---- 1 file changed, 207 insertions(+), 17 deletions(-) diff --git a/block/blk-mq-cpumap.c b/block/blk-mq-cpumap.c index 705da074ad6c..f953714d190c 100644 --- a/block/blk-mq-cpumap.c +++ b/block/blk-mq-cpumap.c @@ -22,7 +22,11 @@ static unsigned int blk_mq_num_queues(const struct cpumask *mask, { unsigned int num; - num = cpumask_weight(mask); + if (housekeeping_enabled(HK_TYPE_IO_QUEUE)) + num = cpumask_weight_and(mask, housekeeping_cpumask(HK_TYPE_IO_QUEUE)); + else + num = cpumask_weight(mask); + return min_not_zero(num, max_queues); } @@ -33,7 +37,8 @@ static unsigned int blk_mq_num_queues(const struct cpumask *mask, * ignored. * * Calculates the number of queues to be used for a multiqueue - * device based on the number of possible CPUs. + * device based on the number of possible CPUs. This helper + * takes isolcpus settings into account. */ unsigned int blk_mq_num_possible_queues(unsigned int max_queues) { @@ -48,7 +53,8 @@ EXPORT_SYMBOL_GPL(blk_mq_num_possible_queues); * ignored. * * Calculates the number of queues to be used for a multiqueue - * device based on the number of online CPUs. + * device based on the number of online CPUs. This helper + * takes isolcpus settings into account. */ unsigned int blk_mq_num_online_queues(unsigned int max_queues) { @@ -56,23 +62,139 @@ unsigned int blk_mq_num_online_queues(unsigned int max_queues) } EXPORT_SYMBOL_GPL(blk_mq_num_online_queues); +static bool blk_mq_validate(struct blk_mq_queue_map *qmap, + const unsigned long *active_hctx, + const struct cpumask *online_mask) +{ + /* + * Verify if the mapping is usable when housekeeping + * configuration is enabled + */ + for (int queue = 0; queue < qmap->nr_queues; queue++) { + int cpu; + + if (test_bit(queue, active_hctx)) { + /* + * This hctx has at least one online CPU thus it + * is able to serve any assigned isolated CPU. + */ + continue; + } + + /* + * There is no housekeeping online CPU for this hctx, all + * good as long as all non-housekeeping CPUs are also + * offline. + */ + for_each_cpu(cpu, online_mask) { + if (qmap->mq_map[cpu] != qmap->queue_offset + queue) + continue; + + pr_warn("Unable to create a usable CPU-to-queue mapping with the given constraints\n"); + return false; + } + } + + return true; +} + +static void blk_mq_map_fallback(struct blk_mq_queue_map *qmap) +{ + unsigned int cpu; + + /* + * Map all CPUs to the first hctx of this specific map to ensure + * at least one online CPU is serving it, respecting the map's + * boundaries so secondary maps do not route into the default map. + */ + for_each_possible_cpu(cpu) + qmap->mq_map[cpu] = qmap->queue_offset; +} + void blk_mq_map_queues(struct blk_mq_queue_map *qmap) { - const struct cpumask *masks; + struct cpumask *masks; + const struct cpumask *constraint; unsigned int queue, cpu, nr_masks; + unsigned long *active_hctx; + cpumask_var_t online_mask; - masks = group_cpus_evenly(qmap->nr_queues, &nr_masks); - if (!masks) { - for_each_possible_cpu(cpu) - qmap->mq_map[cpu] = qmap->queue_offset; - return; - } + active_hctx = bitmap_zalloc(qmap->nr_queues, GFP_KERNEL); + if (!active_hctx) + goto fallback; - for (queue = 0; queue < qmap->nr_queues; queue++) { - for_each_cpu(cpu, &masks[queue % nr_masks]) + if (!alloc_cpumask_var(&online_mask, GFP_KERNEL)) + goto free_fallback_hctx; + + /* + * Snapshot online CPUs to prevent TOCTOU races between the + * mapping phase and the validation phase. + */ + cpumask_copy(online_mask, cpu_online_mask); + + if (housekeeping_enabled(HK_TYPE_IO_QUEUE)) + constraint = housekeeping_cpumask(HK_TYPE_IO_QUEUE); + else + constraint = cpu_possible_mask; + + /* Map CPUs to the hardware contexts (hctx) */ + masks = group_mask_cpus_evenly(qmap->nr_queues, constraint, &nr_masks); + if (!masks) + goto free_fallback; + + /* + * Iterate directly over the generated CPU masks. + * Calculate the final, highest hardware queue index that maps to this + * mask. This skips all intermediate overwrites and safely evaluates + * active_hctx only for queues that survive the mapping. + */ + for (unsigned int idx = 0; idx < nr_masks; idx++) { + bool active = false; + queue = qmap->nr_queues - 1 - + ((qmap->nr_queues - 1 - idx) % nr_masks); + + for_each_cpu(cpu, &masks[idx]) { qmap->mq_map[cpu] = qmap->queue_offset + queue; + + if (!active && cpumask_test_cpu(cpu, online_mask)) { + __set_bit(queue, active_hctx); + active = true; + } + } + } + + /* + * If all CPUs in the generated masks are offline, the active_hctx + * bitmap will be empty. Attempting to route unassigned CPUs to an + * empty bitmap will map them out-of-bounds. Fall back instead. + */ + if (bitmap_empty(active_hctx, qmap->nr_queues)) + goto free_fallback; + + /* Map any unassigned CPU evenly to the hardware contexts (hctx) */ + queue = find_first_bit(active_hctx, qmap->nr_queues); + for_each_cpu_andnot(cpu, cpu_possible_mask, constraint) { + qmap->mq_map[cpu] = qmap->queue_offset + queue; + queue = find_next_bit_wrap(active_hctx, qmap->nr_queues, queue + 1); } + + if (!blk_mq_validate(qmap, active_hctx, online_mask)) + goto free_fallback; + kfree(masks); + free_cpumask_var(online_mask); + bitmap_free(active_hctx); + + return; + +free_fallback: + kfree(masks); + free_cpumask_var(online_mask); +free_fallback_hctx: + bitmap_free(active_hctx); + +fallback: + blk_mq_map_fallback(qmap); } EXPORT_SYMBOL_GPL(blk_mq_map_queues); @@ -109,24 +231,92 @@ void blk_mq_map_hw_queues(struct blk_mq_queue_map *qmap, struct device *dev, unsigned int offset) { - const struct cpumask *mask; + cpumask_var_t mask, online_mask; + const struct cpumask *constraint; + unsigned long *active_hctx; unsigned int queue, cpu; if (!dev->bus->irq_get_affinity) + goto map_software; + + active_hctx = bitmap_zalloc(qmap->nr_queues, GFP_KERNEL); + if (!active_hctx) + goto fallback; + + if (!zalloc_cpumask_var(&mask, GFP_KERNEL)) { + bitmap_free(active_hctx); goto fallback; + } + + if (!alloc_cpumask_var(&online_mask, GFP_KERNEL)) + goto free_fallback_mask; + if (housekeeping_enabled(HK_TYPE_IO_QUEUE)) + constraint = housekeeping_cpumask(HK_TYPE_IO_QUEUE); + else + constraint = cpu_possible_mask; + + /* + * Snapshot online CPUs to prevent TOCTOU races between the + * mapping phase and the validation phase. + */ + cpumask_copy(online_mask, cpu_online_mask); + + /* Map CPUs to the hardware contexts (hctx) */ for (queue = 0; queue < qmap->nr_queues; queue++) { - mask = dev->bus->irq_get_affinity(dev, queue + offset); - if (!mask) - goto fallback; + const struct cpumask *affinity_mask; + bool active = false; + + affinity_mask = dev->bus->irq_get_affinity(dev, offset + queue); + if (!affinity_mask) + goto free_fallback; - for_each_cpu(cpu, mask) + for_each_cpu(cpu, affinity_mask) { qmap->mq_map[cpu] = qmap->queue_offset + queue; + + cpumask_set_cpu(cpu, mask); + if (!active && cpumask_test_cpu(cpu, online_mask) && + cpumask_test_cpu(cpu, constraint)) { + __set_bit(queue, active_hctx); + active = true; + } + } + } + + /* + * If all CPUs assigned to this map are offline, the bitmap will + * be empty. Fall back instead of routing out of bounds. + */ + if (bitmap_empty(active_hctx, qmap->nr_queues)) + goto free_fallback; + + /* Map any unassigned CPU evenly to the hardware contexts (hctx) */ + queue = find_first_bit(active_hctx, qmap->nr_queues); + for_each_cpu_andnot(cpu, cpu_possible_mask, mask) { + qmap->mq_map[cpu] = qmap->queue_offset + queue; + queue = find_next_bit_wrap(active_hctx, qmap->nr_queues, queue + 1); } + if (!blk_mq_validate(qmap, active_hctx, online_mask)) + goto free_fallback; + + bitmap_free(active_hctx); + free_cpumask_var(mask); + free_cpumask_var(online_mask); + return; +free_fallback: + free_cpumask_var(online_mask); +free_fallback_mask: + bitmap_free(active_hctx); + free_cpumask_var(mask); + fallback: + blk_mq_map_fallback(qmap); + return; + +map_software: blk_mq_map_queues(qmap); } EXPORT_SYMBOL_GPL(blk_mq_map_hw_queues); -- 2.51.0