linux-kernel - Re: [PATCH v2 01/17] mm: drop "wait" parameter from write_one

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Date:   Wed, 12 Apr 2017 07:27:26 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Jeff Layton <jlayton@...hat.com>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        akpm@...ux-foundation.org, tytso@....edu, jack@...e.cz,
        neilb@...e.com, viro@...iv.linux.org.uk
Subject: Re: [PATCH v2 01/17] mm: drop "wait" parameter from write_one_page

On Wed, Apr 12, 2017 at 08:05:58AM -0400, Jeff Layton wrote:
> The callers all set it to 1. Also, make it clear that this function will
> not set any sort of AS_* error, and that the caller must do so if
> necessary. No existing caller uses this on normal files, so none of them
> need it.

So ... anyone who doesn't check the error code loses an error indication.

> +++ b/fs/jfs/jfs_metapage.c
> @@ -711,7 +711,7 @@ void force_metapage(struct metapage *mp)
>  	get_page(page);
>  	lock_page(page);
>  	set_page_dirty(page);
> -	write_one_page(page, 1);
> +	write_one_page(page);
>  	clear_bit(META_forcewrite, &mp->flag);
>  	put_page(page);
>  }
> @@ -756,7 +756,7 @@ void release_metapage(struct metapage * mp)
>  		set_page_dirty(page);
>  		if (test_bit(META_sync, &mp->flag)) {
>  			clear_bit(META_sync, &mp->flag);
> -			write_one_page(page, 1);
> +			write_one_page(page);
>  			lock_page(page); /* write_one_page unlocks the page */
>  		}
>  	} else if (mp->lsn)	/* discard_metapage doesn't remove it */

This looks quite bad.  If my reading is right, these pages are part of
the journal.  I think somebody who knows JFS needs to figure out what
should happen here ...

> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 00a8fa7e366a..f25b76486645 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2187,7 +2187,7 @@ extern void filemap_map_pages(struct vm_fault *vmf,
>  extern int filemap_page_mkwrite(struct vm_fault *vmf);
>  
>  /* mm/page-writeback.c */
> -int write_one_page(struct page *page, int wait);
> +int write_one_page(struct page *page);
>  void task_dirty_inc(struct task_struct *tsk);
>  
>  /* readahead.c */

Can we mark this as __must_check so JFS picks up a couple of warnings?

Reviewed-by: Matthew Wilcox <mawilcox@...rosoft.com>