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Tue, 20 Oct 2026 10:44:47 -0700 From: Nirmoy Das To: CC: , , , , , , , , Nirmoy Das , Subject: [PATCH] blk-mq: restore shared-tag flag after hctx reallocation Date: Tue, 20 Oct 2026 10:44:35 -0700 Message-ID: <20261020174435.1527425-1-nirmoyd@nvidia.com> X-Mailer: git-send-email 2.43.0 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-ClientProxiedBy: rnnvmail203.nvidia.com (10.129.68.9) To rnnvmail201.nvidia.com (10.129.68.8) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SJ1PEPF000026C8:EE_|DS4PR12MB634945:EE_ X-MS-Office365-Filtering-Correlation-Id: d31cb993-3425-4f5e-5f14-08df2ed1e1c2 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|23010399003|1800799024|376014|7416014|36860700016|82310400026|56012099006|11063799006|5023799004|261009223027099003|10067099003|18002099003|13003099007; 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A new hctx starts without the bit and a reused hctx keeps whatever it had when it was parked. An NVMe/TCP controller reset goes through this path. With the bit clear and an I/O scheduler, blk_mq_mark_tag_wait() sets SCHED_RESTART without adding a tag waiter and relies on a completion on the same hctx to run the queue again. If other queues on the set hold all the driver tags, this hctx has nothing in flight. Once its submitters block on scheduler tags, nothing runs it again and I/O hangs. Reapply the tag set's shared state after reallocating the hctxs, while the queues are still frozen. Reproduced on v7.3 in an arm64 QEMU/KVM guest with a loopback NVMe/TCP target, four namespaces and mq-deadline. After one controller reset all four namespaces lost TAG_QUEUE_SHARED and fio stalled. With this change the bit survives five resets, and fio completes after a reset. Fixes: 868f2f0b7206 ("blk-mq: dynamic h/w context count") Reported-by: Lev Closes: https://lore.kernel.org/all/00cb01dd3099$c82b66c0$58823440$@zadarastorage.com/ Cc: stable@vger.kernel.org Assisted-by: LLM Specula Signed-off-by: Nirmoy Das --- block/blk-mq.c | 1 + 1 file changed, 1 insertion(+) diff --git a/block/blk-mq.c b/block/blk-mq.c index 00b75eb95dd943a..ec3a7e5300d0e31 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -5188,6 +5188,7 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, set->nr_hw_queues = prev_nr_hw_queues; goto fallback; } + queue_set_hctx_shared(q, set->flags & BLK_MQ_F_TAG_QUEUE_SHARED); blk_mq_map_swqueue(q); } switch_back: -- 2.43.0