On Fri, May 15, 2020 at 05:19:13PM -0700, Bart Van Assche wrote:
> Multiple block drivers use zero_fill_bio() to zero-initialize the data
> buffer used for read operations. Make sure that all pages are zeroed
> instead of only the first if one or more multi-page bvecs are used to
> describe the data buffer.
>
> Cc: Christoph Hellwig <hch@xxxxxx>
> Cc: Ming Lei <ming.lei@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
> ---
> block/bio.c | 27 ++++++++++++++++++++++-----
> include/linux/bio.h | 1 +
> 2 files changed, 23 insertions(+), 5 deletions(-)
>
> diff --git a/block/bio.c b/block/bio.c
> index 1594804fe8bc..48fcafbdae70 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -527,17 +527,34 @@ struct bio *bio_alloc_bioset(gfp_t gfp_mask, unsigned int nr_iovecs,
> }
> EXPORT_SYMBOL(bio_alloc_bioset);
>
> +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;
> + }
> +}
> +EXPORT_SYMBOL(zero_fill_bvec);
> +
> void zero_fill_bio_iter(struct bio *bio, struct bvec_iter start)
> {
> - unsigned long flags;
> struct bio_vec bv;
> struct bvec_iter iter;
>
> __bio_for_each_segment(bv, bio, iter, start) {
The 'bv' from __bio_for_each_segment() is single page bvec, and so far
only [__]bio_for_each_bvec iterates over multi-page bvec.
So nothing to be fixed and this patch isn't necessary.
Thanks,
Ming
