[PATCH] nvmet: fix a possible leak when destroy a ctrl during qp establishment

[Keith Busch]

On Mon, May 27, 2024 at 10:38:52PM +0300, Sagi Grimberg wrote:
> In nvmet_sq_destroy we capture sq->ctrl early and if it is non-NULL we
> know that a ctrl was allocated (in the admin connect request handler)
> and we need to release pending AERs, clear ctrl->sqs and sq->ctrl
> (for nvme-loop primarily), and drop the final reference on the ctrl.
> 
> However, a small window is possible where nvmet_sq_destroy starts (as
> a result of the client giving up and disconnecting) concurrently with
> the nvme admin connect cmd (which may be in an early stage). But *before*
> kill_and_confirm of sq->ref (i.e. the admin connect managed to get an sq
> live reference). In this case, sq->ctrl was allocated however after it was
> captured in a local variable in nvmet_sq_destroy.
> This prevented the final reference drop on the ctrl.
> 
> Solve this by re-capturing the sq->ctrl after all inflight request has
> completed, where for sure sq->ctrl reference is final, and move forward
> based on that.
> 
> This issue was observed in an environment with many hosts connecting
> multiple ctrls simoutanuosly, creating a delay in allocating a ctrl
> leading up to this race window.

Thanks, applied to nvme-6.10.