Re: [PATCH] xfs: don't use in-core per-cpu fdblocks for !lazysbcount

[Carlos Maiolino <cmaiolino@redhat.com>]

On Fri, Apr 16, 2021 at 05:10:23PM +0800, Gao Xiang wrote:
> There are many paths which could trigger xfs_log_sb(), e.g.
>   xfs_bmap_add_attrfork()
>     -> xfs_log_sb()
> , which overrided on-disk fdblocks by in-core per-CPU fdblocks.
> 
> However, for !lazysbcount cases, on-disk fdblocks is actually updated
> by xfs_trans_apply_sb_deltas(), and generally it isn't equal to
> in-core fdblocks due to xfs_reserve_block() or whatever, see the
> comment in xfs_unmountfs().
> 
> It could be observed by the following steps reported by Zorro [1]:
> 
> 1. mkfs.xfs -f -l lazy-count=0 -m crc=0 $dev
> 2. mount $dev $mnt
> 3. fsstress -d $mnt -p 100 -n 1000 (maybe need more or less io load)
> 4. umount $mnt
> 5. xfs_repair -n $dev
> 
> yet due to commit f46e5a174655("xfs: fold sbcount quiesce logging
> into log covering"),

> ... xfs_sync_sb() will be triggered even !lazysbcount
> but xfs_log_need_covered() case when xfs_unmountfs(), so hard to
> reproduce on kernel 5.12+.

I think this could be rephrased, but I am not native english-speaker either, so
I can't say much. Maybe...

"xfs_sync_sb() will be triggered if no log covering is needed and !lazysbcount."

> Reported-by: Zorro Lang <zlang@redhat.com>
> Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
> ---
>  fs/xfs/libxfs/xfs_sb.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_sb.c b/fs/xfs/libxfs/xfs_sb.c
> index 60e6d255e5e2..423dada3f64c 100644
> --- a/fs/xfs/libxfs/xfs_sb.c
> +++ b/fs/xfs/libxfs/xfs_sb.c
> @@ -928,7 +928,13 @@ xfs_log_sb(
>  
>  	mp->m_sb.sb_icount = percpu_counter_sum(&mp->m_icount);
>  	mp->m_sb.sb_ifree = percpu_counter_sum(&mp->m_ifree);
> -	mp->m_sb.sb_fdblocks = percpu_counter_sum(&mp->m_fdblocks);
> +	if (!xfs_sb_version_haslazysbcount(&mp->m_sb)) {
> +		struct xfs_dsb	*dsb = bp->b_addr;
> +
> +		mp->m_sb.sb_fdblocks = be64_to_cpu(dsb->sb_fdblocks);
> +	} else {
> +		mp->m_sb.sb_fdblocks = percpu_counter_sum(&mp->m_fdblocks);
> +	}

The patch looks good to me, feel free to add:

Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>

-- 
Carlos