Re: [PATCH 5/5] null_blk: Zero-initialize read buffers in non-memory-backed mode

[Damien Le Moal <Damien.LeMoal@wdc.com>]

On 2020/05/16 9:19, Bart Van Assche wrote:
> This patch suppresses an uninteresting KMSAN complaint without affecting
> performance of the null_blk driver if CONFIG_KMSAN is disabled.
> 
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Ming Lei <ming.lei@redhat.com>
> Cc: Damien Le Moal <damien.lemoal@wdc.com>
> Cc: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
> Cc: Alexander Potapenko <glider@google.com>
> Reported-by: Alexander Potapenko <glider@google.com>
> Signed-off-by: Bart Van Assche <bvanassche@acm.org>
> ---
>  drivers/block/null_blk_main.c | 30 ++++++++++++++++++++++++++++++
>  1 file changed, 30 insertions(+)
> 
> diff --git a/drivers/block/null_blk_main.c b/drivers/block/null_blk_main.c
> index 06f5761fccb6..df1e144eeaa4 100644
> --- a/drivers/block/null_blk_main.c
> +++ b/drivers/block/null_blk_main.c
> @@ -1250,8 +1250,38 @@ static inline blk_status_t null_handle_memory_backed(struct nullb_cmd *cmd,
>  	return errno_to_blk_status(err);
>  }
>  
> +static void nullb_zero_rq_data_buffer(const struct request *rq)
> +{
> +	struct req_iterator iter;
> +	struct bio_vec bvec;
> +
> +	rq_for_each_bvec(bvec, rq, iter)
> +		zero_fill_bvec(&bvec);
> +}
> +
> +static void nullb_zero_read_cmd_buffer(struct nullb_cmd *cmd)
> +{
> +	struct nullb_device *dev = cmd->nq->dev;
> +
> +	if (dev->queue_mode == NULL_Q_BIO && bio_op(cmd->bio) == REQ_OP_READ)
> +		zero_fill_bio(cmd->bio);
> +	else if (req_op(cmd->rq) == REQ_OP_READ)
> +		nullb_zero_rq_data_buffer(cmd->rq);
> +}

Shouldn't the definition of these two functions be under a "#ifdef CONFIG_KMSAN" ?

> +
> +/* Complete a request. Only called if dev->memory_backed == 0. */
>  static inline void nullb_complete_cmd(struct nullb_cmd *cmd)
>  {
> +	/*
> +	 * Since root privileges are required to configure the null_blk
> +	 * driver, it is fine that this driver does not initialize the
> +	 * data buffers of read commands. Zero-initialize these buffers
> +	 * anyway if KMSAN is enabled to prevent that KMSAN complains
> +	 * about null_blk not initializing read data buffers.
> +	 */
> +	if (IS_ENABLED(CONFIG_KMSAN))
> +		nullb_zero_read_cmd_buffer(cmd);
> +
>  	/* Complete IO by inline, softirq or timer */
>  	switch (cmd->nq->dev->irqmode) {
>  	case NULL_IRQ_SOFTIRQ:
> 


-- 
Damien Le Moal
Western Digital Research