Re: [PATCH v5 1/4] kernfs: add a WARN_ON_ONCE if ->close is set

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Thu, Aug 08, 2024 at 12:33:37PM -0600, Martin Oliveira wrote:
> The next patch is going to remove .page_mkwrite from kernfs and will
> WARN if an mmap implementation sets .page_mkwrite.
> 
> In preparation for that change, and to make it consistent, add a WARN to
> the ->close check.
> 
> Co-developed-by: Logan Gunthorpe <logang@deltatee.com>
> Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
> Signed-off-by: Martin Oliveira <martin.oliveira@eideticom.com>
> ---
>  fs/kernfs/file.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
> index 8502ef68459b..72cc51dcf870 100644
> --- a/fs/kernfs/file.c
> +++ b/fs/kernfs/file.c
> @@ -479,7 +479,7 @@ static int kernfs_fop_mmap(struct file *file, struct vm_area_struct *vma)
>  	 * It is not possible to successfully wrap close.
>  	 * So error if someone is trying to use close.
>  	 */
> -	if (vma->vm_ops && vma->vm_ops->close)
> +	if (WARN_ON_ONCE(vma->vm_ops && vma->vm_ops->close))

So you just rebooted a machine that hits this, loosing data everywhere.
Not nice :(