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References: <20200815035637.15319-1-phillip@squashfs.org.uk>
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From:   Guenter Roeck <groeck@google.com>
Date:   Fri, 14 Aug 2020 21:30:33 -0700
Message-ID: <CABXOdTcJDub=ffmwn4_Xn0chxdwwu4jNFrh9o3HVVH1Mzt4iSA@mail.gmail.com>
Subject: Re: [PATCH] squashfs: avoid bio_alloc() failure with 1Mbyte blocks
To:     Phillip Lougher <phillip@squashfs.org.uk>
Cc:     linux-kernel <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Philippe Liard <pliard@google.com>, hch@lst.de,
        adrien+dev@schischi.me, Guenter Roeck <groeck@chromium.org>,
        Daniel Rosenberg <drosen@google.com>,
        Nicolas Prochazka <nicolas.prochazka@gmail.com>,
        Tomoatsu Shimada <shimada@walbrix.com>
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On Fri, Aug 14, 2020 at 8:57 PM Phillip Lougher <phillip@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.prochazka@gmail.com>
> Reported-by: Tomoatsu Shimada <shimada@walbrix.com>
> Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk>

Fixes: 93e72b3c612a ("squashfs: migrate from ll_rw_block usage to BIO")
Reviewed-by: Guenter Roeck <groeck@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
>