Re: [PATCH v2 1/1] writeback: don't block sync(2) for filesystems with no data integrity guarantees

["David Hildenbrand (Arm)" <david@kernel.org>]

On 3/19/26 20:45, Joanne Koong wrote:
> Add a SB_I_NO_DATA_INTEGRITY superblock flag for filesystems that cannot
> guarantee data persistence on sync (eg fuse). For superblocks with this
> flag set, sync(2) kicks off writeback of dirty inodes but does not wait
> for the flusher threads to complete the writeback.
> 
> This replaces the per-inode AS_NO_DATA_INTEGRITY mapping flag added in
> commit f9a49aa302a0 ("fs/writeback: skip AS_NO_DATA_INTEGRITY mappings
> in wait_sb_inodes()"). The flag belongs at the superblock level because
> data integrity is a filesystem-wide property, not a per-inode one.
> Having this flag at the superblock level allows us to skip the logic in
> sync_inodes_sb() entirely, rather than iterating every dirty inode in
> wait_sb_inodes() only to skip each inode individually.

Makes sense to me.

[...]

>  	if (sb->s_user_ns != &init_user_ns)
>  		sb->s_iflags |= SB_I_UNTRUSTED_MOUNTER;
>  	sb->s_flags &= ~(SB_NOSEC | SB_I_VERSION);
> diff --git a/fs/sync.c b/fs/sync.c
> index 942a60cfedfb..aedbf723830a 100644
> --- a/fs/sync.c
> +++ b/fs/sync.c
> @@ -73,7 +73,12 @@ EXPORT_SYMBOL(sync_filesystem);
>  
>  static void sync_inodes_one_sb(struct super_block *sb, void *arg)
>  {
> -	if (!sb_rdonly(sb))
> +	if (sb_rdonly(sb))
> +		return;
> +

Should we move some of the comment you deleting over here?

> +	if (sb->s_iflags & SB_I_NO_DATA_INTEGRITY)
> +		wakeup_flusher_threads_bdi(sb->s_bdi, WB_REASON_SYNC);
> +	else
>  		sync_inodes_sb(sb);
>  }
I was wondering whether that handling should be moved to
sync_inodes_sb(), so it would catch any (existing+future) callers.

Alternatively, we could catch abuse by adding a warning to sync_inodes_sb.

-- 
Cheers,

David