On Fri, Aug 14, 2020 at 8:57 PM Phillip Lougher <phil...@squashfs.org.uk> wrote:
>
> This is a regression introduced by the "migrate from ll_rw_block usage
> to BIO" patch.
>
> Bio_alloc() is limited to 256 pages (1 Mbyte). This can cause a
> failure when reading 1 Mbyte block filesystems. The problem is
> a datablock can be fully (or almost uncompressed), requiring 256
> pages, but, because blocks are not aligned to page boundaries, it
> may require 257 pages to read.
>
> Bio_kmalloc() can handle 1024 pages, and so use this for the
> edge condition.
>
> Reported-by: Nicolas Prochazka <nicolas.procha...@gmail.com>
> Reported-by: Tomoatsu Shimada <shim...@walbrix.com>
> Signed-off-by: Phillip Lougher <phil...@squashfs.org.uk>
Fixes: 93e72b3c612a ("squashfs: migrate from ll_rw_block usage to BIO")
Reviewed-by: Guenter Roeck <gro...@chromium.org>
> ---
> fs/squashfs/block.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/fs/squashfs/block.c b/fs/squashfs/block.c
> index 76bb1c846845..8a19773b5a0b 100644
> --- a/fs/squashfs/block.c
> +++ b/fs/squashfs/block.c
> @@ -87,7 +87,11 @@ static int squashfs_bio_read(struct super_block *sb, u64
> index, int length,
> int error, i;
> struct bio *bio;
>
> - bio = bio_alloc(GFP_NOIO, page_count);
> + if (page_count <= BIO_MAX_PAGES)
> + bio = bio_alloc(GFP_NOIO, page_count);
> + else
> + bio = bio_kmalloc(GFP_NOIO, page_count);
> +
> if (!bio)
> return -ENOMEM;
>
> --
> 2.20.1
>
