Re: [PATCH v2 4/4] null_blk: Zero-initialize read buffers in non-memory-backed mode

[Ming Lei <ming.lei@redhat.com>]

On Sun, May 17, 2020 at 06:48:07PM -0700, 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>
> Tested-by: Alexander Potapenko <glider@google.com>
> Signed-off-by: Bart Van Assche <bvanassche@acm.org>
> ---
>  drivers/block/null_blk_main.c | 50 +++++++++++++++++++++++++++++++++++
>  1 file changed, 50 insertions(+)
> 
> diff --git a/drivers/block/null_blk_main.c b/drivers/block/null_blk_main.c
> index 06f5761fccb6..0c1df6ecb30b 100644
> --- a/drivers/block/null_blk_main.c
> +++ b/drivers/block/null_blk_main.c
> @@ -1250,8 +1250,58 @@ static inline blk_status_t null_handle_memory_backed(struct nullb_cmd *cmd,
>  	return errno_to_blk_status(err);
>  }
>  
> +static void zero_fill_bvec(const struct bio_vec *bvec)
> +{
> +	struct page *page = bvec->bv_page;
> +	u32 offset = bvec->bv_offset;
> +	u32 left = bvec->bv_len;
> +
> +	while (left) {
> +		u32 len = min_t(u32, left, PAGE_SIZE - offset);
> +		void *kaddr;
> +
> +		kaddr = kmap_atomic(page);
> +		memset(kaddr + offset, 0, len);
> +		flush_dcache_page(page);
> +		kunmap_atomic(kaddr);
> +		page++;
> +		left -= len;
> +		offset = 0;
> +	}
> +}
> +
> +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);
> +}

Not necessary to add zero_fill_bvec(), and it can be done in the
following two line code:

	__rq_for_each_bio(bio, rq)
		zero_fill_bio(bio);


Thanks,
Ming