linux-kernel - Re: [PATCH AUTOSEL 6.1 20/22] block: Allow bio_iov_iter_get_pages() with bio->bi

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Date:   Mon, 11 Sep 2023 11:54:32 +0200
From:   Pavel Machek <pavel@...x.de>
To:     Sasha Levin <sashal@...nel.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Kent Overstreet <kent.overstreet@...ux.dev>,
        Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org
Subject: Re: [PATCH AUTOSEL 6.1 20/22] block: Allow bio_iov_iter_get_pages()
 with bio->bi_bdev unset

Hi!

> From: Kent Overstreet <kent.overstreet@...ux.dev>
> 
> [ Upstream commit 168145f617d57bf4e474901b7ffa869337a802e6 ]
> 
> bio_iov_iter_get_pages() trims the IO based on the block size of the
> block device the IO will be issued to.
> 
> However, bcachefs is a multi device filesystem; when we're creating the
> bio we don't yet know which block device the bio will be submitted to -
> we have to handle the alignment checks elsewhere.
> 
> Thus this is needed to avoid a null ptr deref.

We are certainly not going to backport bcachefs to -stable. Please
drop.

BR,
								Pavel

> +++ b/block/bio.c
> @@ -1198,7 +1198,7 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
>  	struct page **pages = (struct page **)bv;
>  	ssize_t size, left;
>  	unsigned len, i = 0;
> -	size_t offset, trim;
> +	size_t offset;
>  	int ret = 0;
>  
>  	/*
> @@ -1223,10 +1223,12 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
>  
>  	nr_pages = DIV_ROUND_UP(offset + size, PAGE_SIZE);
>  
> -	trim = size & (bdev_logical_block_size(bio->bi_bdev) - 1);
> -	iov_iter_revert(iter, trim);
> +	if (bio->bi_bdev) {
> +		size_t trim = size & (bdev_logical_block_size(bio->bi_bdev) - 1);
> +		iov_iter_revert(iter, trim);
> +		size -= trim;
> +	}
>  
> -	size -= trim;
>  	if (unlikely(!size)) {
>  		ret = -EFAULT;
>  		goto out;

-- 
DENX Software Engineering GmbH,        Managing Director: Erika Unter
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany

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