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[131.94.134.89]) by smtp.gmail.com with ESMTPSA id ada2fe7eead31-63ccf18cfc4sm390027137.2.2026.05.15.00.12.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 15 May 2026 00:12:49 -0700 (PDT) From: Chao Shi To: linux-nvme@lists.infradead.org, Keith Busch Cc: Christoph Hellwig , Sagi Grimberg , Jens Axboe , Tatsuya Sasaki , Maurizio Lombardi , linux-kernel@vger.kernel.org, Sungwoo Kim , Dave Tian , Weidong Zhu Subject: [PATCH v2] nvme: reserve a keep-alive admin tag for all transports Date: Fri, 15 May 2026 03:12:48 -0400 Message-ID: <20260515071248.2689513-1-coshi036@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit nvme_keep_alive_work() always allocates with BLK_MQ_REQ_RESERVED, but nvme_alloc_admin_tag_set() only sets reserved_tags for fabrics. Since commit b58da2d270db ("nvme: update keep alive interval when kato is modified"), userspace can start keep-alive on any transport via Set Features (KATO), after which the allocation trips WARN_ON_ONCE() in blk_mq_get_tag() and fails with -EWOULDBLOCK: nvme nvme0: keep-alive failed: -11 Per NVMe 2.0a section 5.27.1.12 and the transport binding wording, PCIe MAY support KATO. Reserve one admin tag on all transports so the host is ready when a controller accepts the feature. Fabrics keeps two, the second being for the connect command. A quirk-based approach was considered but no PCIe controller documented to declare KAS != 0 was found (two enterprise SSDs tested locally report KAS=0), so an allowlist has no entries today. Link: https://lore.kernel.org/linux-nvme/20260428022911.1288485-1-coshi036@gmail.com/ Fixes: b58da2d270db ("nvme: update keep alive interval when kato is modified") Found by FuzzNvme (Syzkaller with FEMU fuzzing framework). Acked-by: Sungwoo Kim Acked-by: Dave Tian Acked-by: Weidong Zhu Signed-off-by: Chao Shi --- Reproducer (run as root on an unpatched kernel with a PCIe NVMe device): #include #include #include #include #include int main(void) { struct nvme_admin_cmd cmd = {0}; int fd = open("/dev/nvme0", O_RDWR); if (fd < 0) { perror("open"); return 1; } cmd.opcode = 0x09; /* SET_FEATURES */ cmd.cdw10 = 0x0f; /* Feature ID: KATO */ cmd.cdw11 = 5; /* KATO = 5 seconds */ if (ioctl(fd, NVME_IOCTL_ADMIN_CMD, &cmd) < 0) { perror("ioctl"); return 1; } return 0; } Within ~kato/2 seconds after the program exits, dmesg shows: nvme nvme0: keep alive interval updated from 0 ms to 5000 ms WARNING: CPU: 0 PID: ... at block/blk-mq-tag.c:148 blk_mq_get_tag+... nvme nvme0: keep-alive failed: -11 Changes since v1: - Add spec citation (NVMe 2.0a 5.27.1.12 + transport binding wording) clarifying that PCIe MAY support KATO. - Discuss the quirk-based alternative suggested in v1 review and note that no PCIe controller declaring KAS != 0 is documented today (two enterprise SSDs tested locally report KAS=0). - Add Link: to v1 thread. drivers/nvme/host/core.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c index 7bf228df6001..6db02ecde6d1 100644 --- a/drivers/nvme/host/core.c +++ b/drivers/nvme/host/core.c @@ -4850,8 +4850,13 @@ int nvme_alloc_admin_tag_set(struct nvme_ctrl *ctrl, struct blk_mq_tag_set *set, memset(set, 0, sizeof(*set)); set->ops = ops; set->queue_depth = NVME_AQ_MQ_TAG_DEPTH; + /* + * Reserve one tag for keep-alive, which is allocated with + * BLK_MQ_REQ_RESERVED and can be enabled on any transport via the + * KATO feature. Fabrics needs a second reserved tag for connect. + */ + set->reserved_tags = 1; if (ctrl->ops->flags & NVME_F_FABRICS) - /* Reserved for fabric connect and keep alive */ set->reserved_tags = 2; set->numa_node = ctrl->numa_node; if (ctrl->ops->flags & NVME_F_BLOCKING) -- 2.43.0