linux-kernel - Re: [PATCH v3 08/10] dm: handle error from blk_ksm

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Date:   Wed, 16 Jun 2021 20:23:40 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Satya Tangirala <satyat@...gle.com>
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH v3 08/10] dm: handle error from blk_ksm_register()

On Fri, Jun 04, 2021 at 07:58:58PM +0000, Satya Tangirala wrote:
> Handle any error from blk_ksm_register() in the callers. Previously,
> the callers ignored the return value because blk_ksm_register() wouldn't
> fail as long as the request_queue didn't have integrity support too, but
> as this is no longer the case, it's safer for the callers to just handle
> the return value appropriately.
> 
> Signed-off-by: Satya Tangirala <satyat@...gle.com>
> ---
>  drivers/md/dm-table.c | 16 +++++++++++++++-
>  1 file changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
> index 29cbfc3e3c4b..e44f304b5c1a 100644
> --- a/drivers/md/dm-table.c
> +++ b/drivers/md/dm-table.c
> @@ -1354,7 +1354,21 @@ static void dm_update_keyslot_manager(struct request_queue *q,
>  
>  	/* Make the ksm less restrictive */
>  	if (!q->ksm) {
> -		blk_ksm_register(t->ksm, q);
> +		/*
> +		 * This WARN_ON should never trigger since t->ksm isn't be
> +		 * "empty" (i.e. will support at least 1 crypto capability), the
> +		 * request queue doesn't support integrity (since
> +		 * dm_table_construct_keyslot_manager() checks that), and
> +		 * it also satisfies all the block layer constraints
> +		 * "sufficiently" (as in the constraints of the DM device's
> +		 * request queue won't preclude any of the intersection of the
> +		 * supported capabilities of the underlying devices, since if
> +		 * some capability were precluded by the DM device's request
> +		 * queue's constraints, that capability would also have been
> +		 * precluded by one of the child device's request queues)
> +		 */
> +		if (WARN_ON(!blk_ksm_register(t->ksm, q)))
> +			dm_destroy_keyslot_manager(t->ksm);

This comment seems to be in the wrong place, as dm_update_keyslot_manager()
already assumes that the crypto capabilities are either staying the same or
expanding.  This isn't something new that this WARN_ON() introduces.

I think this explanation should go in dm_table_construct_keyslot_manager()
instead, as that is where the new set of crypto capabilities is built.
I.e. in dm_table_construct_keyslot_manager() we should explain how we "know"
that the new set will really be equal or greater.

- Eric