Re: [PATCH v2 1/1] fs/writeback: skip AS_NO_DATA_INTEGRITY mappings in wait_sb_inodes()

[Andrew Morton <akpm@linux-foundation.org>]

On Sun, 14 Dec 2025 19:00:43 -0800 Joanne Koong <joannelkoong@gmail.com> wrote:

> Skip waiting on writeback for inodes that belong to mappings that do not
> have data integrity guarantees (denoted by the AS_NO_DATA_INTEGRITY
> mapping flag).
> 
> This restores fuse back to prior behavior where syncs are no-ops. This
> is needed because otherwise, if a system is running a faulty fuse
> server that does not reply to issued write requests, this will cause
> wait_sb_inodes() to wait forever.
> 
> Fixes: 0c58a97f919c ("fuse: remove tmp folio for writebacks and internal rb tree")
> Reported-by: Athul Krishna <athul.krishna.kr@protonmail.com>
> Reported-by: J. Neuschäfer <j.neuschaefer@gmx.net>
> Cc: stable@vger.kernel.org
> Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
>
> ..
>
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -2751,7 +2751,8 @@ static void wait_sb_inodes(struct super_block *sb)
>  		 * do not have the mapping lock. Skip it here, wb completion
>  		 * will remove it.
>  		 */
> -		if (!mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK))
> +		if (!mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK) ||
> +		    mapping_no_data_integrity(mapping))
>  			continue;

It's not obvious why a no-data-integrity mapping would want to skip
writeback - what do these things have to do with each other?

So can we please have a v2 which has a comment here explaining this to the
reader?