Re: [PATCH v5 07/11] iomap: fix iomap_dio_zero() for fs bs > system page size

[Matthew Wilcox <willy@xxxxxxxxxxxxx>]

On Fri, May 03, 2024 at 02:53:49AM -0700, Luis Chamberlain wrote:
> +	bio = iomap_dio_alloc_bio(iter, dio, BIO_MAX_VECS,
> +				  REQ_OP_WRITE | REQ_SYNC | REQ_IDLE);
>  	fscrypt_set_bio_crypt_ctx(bio, inode, pos >> inode->i_blkbits,
>  				  GFP_KERNEL);
> +
>  	bio->bi_iter.bi_sector = iomap_sector(&iter->iomap, pos);
>  	bio->bi_private = dio;
>  	bio->bi_end_io = iomap_dio_bio_end_io;
>  
> -	__bio_add_page(bio, page, len, 0);
> +	while (len) {
> +		unsigned int io_len = min_t(unsigned int, len, PAGE_SIZE);
> +
> +		__bio_add_page(bio, page, io_len, 0);
> +		len -= io_len;
> +	}
>  	iomap_dio_submit_bio(iter, dio, bio, pos);

If the len is more than PAGE_SIZE * BIO_MAX_VECS, __bio_add_page()
will fail silently.  I hate this interface.

You should be doing something like ...

	while (len) {
		unsigned int io_len = min_t(unsigned int, len, PAGE_SIZE);

		while (!bio || bio_add_page() < io_len) {
			if (bio)
				iomap_dio_submit_bio(iter, dio, bio, pos);
			bio = iomap_dio_alloc_bio(iter, dio, BIO_MAX_VECS,
					REQ_OP_WRITE | REQ_SYNC | REQ_IDLE);
		 	fscrypt_set_bio_crypt_ctx(bio, inode,
					pos >> inode->i_blkbits, GFP_KERNEL);
		}
	}