Re: [PATCH] ceph: switch back to testing for NULL folio->private in ceph_dirty_folio

[Xiubo Li <xiubli@redhat.com>]

On 6/10/22 11:40 PM, Jeff Layton wrote:
> Willy requested that we change this back to warning on folio->private
> being non-NULl. He's trying to kill off the PG_private flag, and so we'd
> like to catch where it's non-NULL.
>
> Add a VM_WARN_ON_FOLIO (since it doesn't exist yet) and change over to
> using that instead of VM_BUG_ON_FOLIO along with testing the ->private
> pointer.
>
> Cc: Matthew Wilcox <willy@infradead.org>
> Signed-off-by: Jeff Layton <jlayton@kernel.org>
> ---
>   fs/ceph/addr.c          | 2 +-
>   include/linux/mmdebug.h | 9 +++++++++
>   2 files changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/fs/ceph/addr.c b/fs/ceph/addr.c
> index b43cc01a61db..b24d6bdb91db 100644
> --- a/fs/ceph/addr.c
> +++ b/fs/ceph/addr.c
> @@ -122,7 +122,7 @@ static bool ceph_dirty_folio(struct address_space *mapping, struct folio *folio)
>   	 * Reference snap context in folio->private.  Also set
>   	 * PagePrivate so that we get invalidate_folio callback.
>   	 */
> -	VM_BUG_ON_FOLIO(folio_test_private(folio), folio);
> +	VM_WARN_ON_FOLIO(folio->private, folio);
>   	folio_attach_private(folio, snapc);
>   
>   	return ceph_fscache_dirty_folio(mapping, folio);
> diff --git a/include/linux/mmdebug.h b/include/linux/mmdebug.h
> index d7285f8148a3..5107bade2ab2 100644
> --- a/include/linux/mmdebug.h
> +++ b/include/linux/mmdebug.h
> @@ -54,6 +54,15 @@ void dump_mm(const struct mm_struct *mm);
>   	}								\
>   	unlikely(__ret_warn_once);					\
>   })
> +#define VM_WARN_ON_FOLIO(cond, folio)		({			\
> +	int __ret_warn = !!(cond);					\
> +									\
> +	if (unlikely(__ret_warn)) {					\
> +		dump_page(&folio->page, "VM_WARN_ON_FOLIO(" __stringify(cond)")");\
> +		WARN_ON(1);						\
> +	}								\
> +	unlikely(__ret_warn);						\
> +})

I have fixed the compile warning reported by kernel test robot by 
defining it in case the DEBUG_VM is disabled in testing branch.

-- Xiubo


>   #define VM_WARN_ON_ONCE_FOLIO(cond, folio)	({			\
>   	static bool __section(".data.once") __warned;			\
>   	int __ret_warn_once = !!(cond);					\