linux-kernel - Re: [PATCH] f2fs: fix to prevent clearing immutable for large folio supported inode

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Message-ID: <CAGsJ_4wjXMXk4YKsYebmtTa5dKVO21b91ieY=foYULWS+DyroQ@mail.gmail.com>
Date: Fri, 9 Jan 2026 16:05:49 +1300
From: Barry Song <21cnbao@...il.com>
To: Chao Yu <chao@...nel.org>
Cc: jaegeuk@...nel.org, linux-f2fs-devel@...ts.sourceforge.net, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] f2fs: fix to prevent clearing immutable for large folio
 supported inode

On Fri, Jan 9, 2026 at 3:47 PM Chao Yu <chao@...nel.org> wrote:
>
> Below testcase can change large folio supported inode from immutable
> to mutable, it's not as expected, let's add a new check condition in
> f2fs_setflags_common() to detect and reject it.
>
> - dd if=/dev/zero of=/mnt/f2fs/test bs=32k count=4
> - f2fs_io setflags immutable /mnt/f2fs/test
> - echo 3 > /proc/sys/vm/drop_caches
>  : to reload inode with large folio
> - f2fs_io read 32 0 1 mmap 0 0 /mnt/f2fs/test
> - f2fs_io clearflags immutable /mnt/f2fs/test
>
> Signed-off-by: Chao Yu <chao@...nel.org>
> ---
>  fs/f2fs/file.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> index ce291f152bc3..f7f9da0b215f 100644
> --- a/fs/f2fs/file.c
> +++ b/fs/f2fs/file.c
> @@ -2155,6 +2155,12 @@ static int f2fs_setflags_common(struct inode *inode, u32 iflags, u32 mask)
>                 }
>         }
>
> +       if ((iflags ^ masked_flags) & F2FS_IMMUTABLE_FL) {
> +               if ((masked_flags & F2FS_IMMUTABLE_FL) &&
> +                       mapping_large_folio_support(inode->i_mapping))
> +                       return -EINVAL;

Hi Yu, I find it a bit odd to prevent unsetting immutable solely
because large folios are in use. If unsetting immutable is considered
unexpected behavior, it should be disallowed regardless of whether
large folios are used, and apply equally in both cases.

I'm not sure whether reverting the large folios setting is the
better approach:
truncate_pagecache(inode, inode->i_size);
mapping_set_folio_order_range(inode->i_mapping, 0, 0);


> +       }
> +
>         fi->i_flags = iflags | (fi->i_flags & ~mask);
>         f2fs_bug_on(F2FS_I_SB(inode), (fi->i_flags & F2FS_COMPR_FL) &&
>                                         (fi->i_flags & F2FS_NOCOMP_FL));
> --
> 2.40.1


Thanks
Barry