Page migration issue with UBIFS

[Kirill A. Shutemov]

On Wed, Mar 16, 2016 at 05:21:56PM +0300, Kirill A. Shutemov wrote:
> On Wed, Mar 16, 2016 at 12:18:50AM +0100, Richard Weinberger wrote:
> > Am 15.03.2016 um 16:37 schrieb Christoph Hellwig:
> > > On Tue, Mar 15, 2016 at 04:32:40PM +0100, Richard Weinberger wrote:
> > >>> Or if ->page_mkwrite() was called, why the page is not dirty?
> > >>
> > >> BTW: UBIFS does not implement ->migratepage(), could this be a problem?
> > > 
> > > This might be the reason.  I can't reall make sense of
> > > buffer_migrate_page, but it seems to migrate buffer_head state to
> > > the new page.
> > > 
> > > I'd love to know why CMA even tries to migrate pages that don't have a
> > > ->migratepage method, this seems incredibly dangerous to me.
> > 
> > FYI, with a dummy ->migratepage() which returns only -EINVAL UBIFS does no
> > longer explode upon page migration.
> > Tomorrow I'll do more tests to make sure.
> 
> Could you check if something like this would fix the issue.
> Completely untested.
> 
> diff --git a/fs/ubifs/file.c b/fs/ubifs/file.c
> index 065c88f8e4b8..9da34120dc5e 100644
> --- a/fs/ubifs/file.c
> +++ b/fs/ubifs/file.c
> @@ -52,6 +52,7 @@
>  #include "ubifs.h"
>  #include <linux/mount.h>
>  #include <linux/slab.h>
> +#include <linux/migrate.h>
>  
>  static int read_block(struct inode *inode, void *addr, unsigned int block,
>  		      struct ubifs_data_node *dn)
> @@ -1452,6 +1453,20 @@ static int ubifs_set_page_dirty(struct page *page)
>  	return ret;
>  }
>  
> +static int ubifs_migrate_page(struct address_space *mapping,
> +		struct page *newpage, struct page *page, enum migrate_mode mode)
> +{
> +	if (PagePrivate(page)) {
> +		SetPagePrivate(newpage);
> +		__set_page_dirty_nobuffers(newpage);
> +	}
> +
> +	if (PageChecked(page))
> +		SetPageChecked(newpage);

These two lines are redundant, migrate_page_copy() would do this for us.

> +
> +	return migrate_page(mapping, newpage, page, mode);
> +}
> +
>  static int ubifs_releasepage(struct page *page, gfp_t unused_gfp_flags)
>  {
>  	/*
> @@ -1591,6 +1606,7 @@ const struct address_space_operations ubifs_file_address_operations = {
>  	.write_end      = ubifs_write_end,
>  	.invalidatepage = ubifs_invalidatepage,
>  	.set_page_dirty = ubifs_set_page_dirty,
> +	.migratepage	= ubifs_migrate_page,
>  	.releasepage    = ubifs_releasepage,
>  };
>  
> -- 
>  Kirill A. Shutemov

-- 
 Kirill A. Shutemov