zram: don't fail to remove zram during unloading module

zram: don't fail to remove zram during unloading module

When the zram module is being unloaded, no one should be using the
zram disks. However even while being unloaded the zram module's
sysfs attributes might be poked at to re-configure zram devices.
This is expected, and kernfs ensures that these operations complete
before device_del() completes.

But reset_store() may set ->claim which will fail zram_remove(), when
this happens, zram_reset_device() is bypassed, and zram->comp can't
be destroyed, so the warning of 'Error: Removing state 63 which has
instances left.' is triggered during unloading module, together with
memory leak and sort of thing.

Fixes the issue by not failing zram_remove() if ->claim is set, and
we actually need to do nothing in case that zram_reset() is running
since del_gendisk() will wait until zram_reset() is done.

Reported-by: Luis Chamberlain <mcgrof@kernel.org>
Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Link: https://lore.kernel.org/r/20211025025426.2815424-3-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>