Re: [PATCH] nvme: Add module reference counting for multipath nvme device

[Wen Xiong <wenxiong@linux.ibm.com>]

On 2026-08-11 08:18, John Garry wrote:

> Can you demonstrate that this is a problem?
> 
For example, the Linux root filesystem is located on a multipath NVMe 
device. During system boot, the reference count of the nvme module is 
zero. As a result, the tester can run rmmod nvme, which causes the 
system to become unstable or crash.

linux was installed on /dev/nvme4n2.
#lsmod|grep nvme
nvme_fabrics          262144  0
nvme                  262144  0 ----> reference count = 0 for nvme 
module.
nvme_core             458752  4 nvme,nvme_fabrics
nvme_keyring          262144  2 nvme_core,nvme_fabrics
nvme_auth             262144  1 nvme_core
#  rmmod nvme
[11312.100786][  T937] BTRFS error (device nvme4n1p2): bdev 
/dev/nvme4n1p2 errs: wr 1, rd 0, flush 0, corrupt 0, gen 0
[11312.100855][  T937] BTRFS error (device nvme4n1p2): bdev 
/dev/nvme4n1p2 errs: wr 2, rd 0, flush 0, corrupt 0, gen 0
[11338.724061][  T624] BTRFS error (device nvme4n1p2 state A): 
Transaction aborted (error -5)
[11338.724075][  T624] BTRFS: error (device nvme4n1p2 state A) in 
__btrfs_update_delayed_inode:1096: errno=-5 IO failure
# ls
ls: reading directory '.': Input/output error

In the current nvme module reference count increase/decrease logic, the 
operation is skipped when the device is a multipath device. As a result, 
the NVMe module reference count remains zero even though the NVMe device 
is actively being used by the multipath stack.

static int nvme_ns_open(struct nvme_ns *ns)
{

         /* should never be called due to GENHD_FL_HIDDEN */
         if (WARN_ON_ONCE(nvme_ns_head_multipath(ns->head)))
                 goto fail;
         if (!nvme_get_ns(ns))
                 goto fail;
         if (!try_module_get(ns->ctrl->ops->module))
                 goto fail_put_ns;

This patch adds module reference count increase/decrease logic in 
nvme_ns_head_open() and nvme_ns_head_release() for the multipath head 
device. This mirrors the behavior of nvme_ns_open() for non-multipath 
devices.

Thanks,
Wendy