Re: [PATCH blktests] nvme/068: add a test for multipath delayed removal

[Chaitanya Kulkarni <chaitanyak@nvidia.com>]

John,

On 4/15/26 03:41, John Garry wrote:
> For NVMe multipath, the delayed removal feature allows the multipath
> gendisk to remain present when all available paths are gone. The purpose of
> this feature is to ensure that we keep the gendisk for intermittent path
> failures.
>
> The delayed removal works on a timer - when all paths are gone, a timer is
> kicked off; once the timer expires and no paths have returned, the gendisk
> is removed.
>
> When all paths are gone and the gendisk is still present, all reads and
> writes to the disk are queued. If a path returns before the timer
> expiration, the timer canceled and the queued IO is submitted;
> otherwise they fail when the timer expires.
>
> This testcase covers two scenarios in separate parts:
> a. test that IOs submitted after all paths are removed (and do not return)
>     fail
> b. test that IOs submitted between all paths removed and a path
>     returning succeed
>
> During the period of the timer being active, it must be ensured that the
> nvme-core module is not removed. Otherwise the driver may not be present
> to handle the timeout expiry. The kernel ensures this by taking a
> reference to the module. Ideally, we would try to remove the module during
> this test to prove that this is not possible (and the kernel behaves as
> expected), but that module will probably not be removable anyway due to
> many references. To test this feature, check that the refcount of the
> nvme-core module is incremented when the delayed timer is active.
>
> Signed-off-by: John Garry<john.g.garry@oracle.com>

Thanks you so much for this testcase.
I've failed to add tests in this areas but this will be absolutely
helpful to have it in regular testing.

Looks good.

Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>

-ck