Re: [PATCH v2] fs: ntfs: Disable NTFS_RW for PPC

[Joel Stanley <joel@jms.id.au>]

On Mon, 22 Nov 2021 at 23:58, Guenter Roeck <linux@roeck-us.net> wrote:
>
> NTFS_RW code allocates page size dependent arrays on the stack. This
> results in build failures if the page size is 64k, which is now the
> default for PPC.

It became the default for PPC_BOOK3S_64, which doesn't include all of
PPC, in f22969a66041 ("powerpc/64s: Default to 64K pages for 64 bit
book3s").

You might want to add a mention of this commit in your commit message.

>
> fs/ntfs/aops.c: In function 'ntfs_write_mst_block':
> fs/ntfs/aops.c:1311:1: error:
>         the frame size of 2240 bytes is larger than 2048 bytes
>
> Increasing the maximum frame size for PPC just to silence this error does
> not really help. It would have to be set to a really large value for 256k
> pages. Such a large frame size could potentially result in stack overruns
> in this code and elsewhere and is therefore not desirable. Disable NTFS_RW
> for PPC instead.
>
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Cc: Stephen Rothwell <sfr@canb.auug.org.au>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
> ---
> v2: Introduce new configuration flag DISABLE_NTFS_RW and use it to disable NTFS_RW
>     for PPC
>
>  fs/ntfs/Kconfig | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/fs/ntfs/Kconfig b/fs/ntfs/Kconfig
> index 1667a7e590d8..324224febb6a 100644
> --- a/fs/ntfs/Kconfig
> +++ b/fs/ntfs/Kconfig
> @@ -49,8 +49,13 @@ config NTFS_DEBUG
>           When reporting bugs, please try to have available a full dump of
>           debugging messages while the misbehaviour was occurring.
>
> +config DISABLE_NTFS_RW
> +       bool
> +       default y if PPC

PPC_64K_PAGES would be more accurate.

I think arm64 was seeing a similar build error, so you could include
ARM64_64K_PAGES as well?

> +
>  config NTFS_RW
>         bool "NTFS write support"
> +       depends on !DISABLE_NTFS_RW
>         depends on NTFS_FS
>         help
>           This enables the partial, but safe, write support in the NTFS driver.
> --
> 2.33.0
>