Re: [PATCH 0/2] nvme: add reference counting for transport modules

[John Garry <john.garry@linux.dev>]

On 8/31/26 16:19, Nilay Shroff wrote:
> Hi,
> 
> This patchset adds reference counting for NVMe transport modules while
> the corresponding multipath head node is open. This prevents the
> underlying transport module from being unloaded while it is still in
> use by the multipath head node. Unloading a transport module while it
> is still in use can result in undefined behavior.
> 

What is the undefined behaviour specifically?

When the ctrl ops module ref counting was originally introduced, the 
commit message mentioned a crash which it solves.

So far for this problem we have seen a report that if we remove the 
module, the mounted FS will have IOs fail. The same can be experienced 
if the admin unbinds the device from the driver. However, I have not 
seen a mention of a crash, kernel data corruption, a hang, etc.


> The second patch adds a Clang context annotation for the shared field
> used to track the number of active head node openers, allowing the
> Clang context analyzer to validate accesses to the field.
> 
> As usual, feedback and suggestions are welcome.
> 
> Thanks!
> 
> Nilay Shroff (2):
>    nvme: keep transport module referenced while head node is open
>    nvme: add context annotation for nvme_ns_head::nr_openers
> 
>   drivers/nvme/host/core.c      | 11 +++++++++--
>   drivers/nvme/host/multipath.c | 37 +++++++++++++++++++++++++++++++++--
>   drivers/nvme/host/nvme.h      | 33 +++++++++++++++++++++++++++++++
>   3 files changed, 77 insertions(+), 4 deletions(-)
>