Re: [PATCH v2] xfs: don't commit sunit/swidth updates to disk if that would cause repair failures

[Brian Foster <bfoster@redhat.com>]

On Fri, Dec 13, 2019 at 08:13:49AM -0800, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.com>
> 
> Alex Lyakas reported[1] that mounting an xfs filesystem with new sunit
> and swidth values could cause xfs_repair to fail loudly.  The problem
> here is that repair calculates the where mkfs should have allocated the
> root inode, based on the superblock geometry.  The allocation decisions
> depend on sunit, which means that we really can't go updating sunit if
> it would lead to a subsequent repair failure on an otherwise correct
> filesystem.
> 
> Port from xfs_repair some code that computes the location of the root
> inode and teach mount to skip the ondisk update if it would cause
> problems for repair.  Along the way we'll update the documentation,
> provide a function for computing the minimum AGFL size instead of
> open-coding it, and cut down some indenting in the mount code.
> 
> Note that we allow the mount to proceed (and new allocations will
> reflect this new geometry) because we've never screened this kind of
> thing before.  We'll have to wait for a new future incompat feature to
> enforce correct behavior, alas.
> 
> Note that the geometry reporting always uses the superblock values, not
> the incore ones, so that is what xfs_info and xfs_growfs will report.
> 
> [1] https://lore.kernel.org/linux-xfs/20191125130744.GA44777@bfoster/T/#m00f9594b511e076e2fcdd489d78bc30216d72a7d
> 
> Reported-by: Alex Lyakas <alex@zadara.com>
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---
> v2: refactor the agfl length calculations, clarify the fsgeometry ioctl
> behavior, fix a bunch of the comments and make it clearer how we compute
> the rootino location
> ---
>  fs/xfs/libxfs/xfs_alloc.c  |   18 ++++++---
>  fs/xfs/libxfs/xfs_ialloc.c |   70 ++++++++++++++++++++++++++++++++++
>  fs/xfs/libxfs/xfs_ialloc.h |    1 
>  fs/xfs/xfs_mount.c         |   90 ++++++++++++++++++++++++++++++--------------
>  fs/xfs/xfs_trace.h         |   21 ++++++++++
>  5 files changed, 166 insertions(+), 34 deletions(-)
> 
...
> diff --git a/fs/xfs/libxfs/xfs_ialloc.h b/fs/xfs/libxfs/xfs_ialloc.h
> index 323592d563d5..72b3468b97b1 100644
> --- a/fs/xfs/libxfs/xfs_ialloc.h
> +++ b/fs/xfs/libxfs/xfs_ialloc.h
...
> @@ -398,28 +431,26 @@ xfs_update_alignment(xfs_mount_t *mp)
>  			}
>  		}
>  
> -		/*
> -		 * Update superblock with new values
> -		 * and log changes
> -		 */
> -		if (xfs_sb_version_hasdalign(sbp)) {
> -			if (sbp->sb_unit != mp->m_dalign) {
> -				sbp->sb_unit = mp->m_dalign;
> -				mp->m_update_sb = true;
> -			}
> -			if (sbp->sb_width != mp->m_swidth) {
> -				sbp->sb_width = mp->m_swidth;
> -				mp->m_update_sb = true;
> -			}
> -		} else {
> +		/* Update superblock with new values and log changes. */
> +		if (!xfs_sb_version_hasdalign(sbp)) {
>  			xfs_warn(mp,
>  	"cannot change alignment: superblock does not support data alignment");
>  			return -EINVAL;
>  		}
> +
> +		if (sbp->sb_unit == mp->m_dalign &&
> +		    sbp->sb_width == mp->m_swidth)
> +			return 0;
> +
> +		xfs_check_new_dalign(mp, mp->m_dalign);
> +
> +		sbp->sb_unit = mp->m_dalign;
> +		sbp->sb_width = mp->m_swidth;
> +		mp->m_update_sb = true;

Isn't this supposed to conditionally update the superblock based on the
rootino calculation?

Brian

>  	} else if ((mp->m_flags & XFS_MOUNT_NOALIGN) != XFS_MOUNT_NOALIGN &&
>  		    xfs_sb_version_hasdalign(&mp->m_sb)) {
> -			mp->m_dalign = sbp->sb_unit;
> -			mp->m_swidth = sbp->sb_width;
> +		mp->m_dalign = sbp->sb_unit;
> +		mp->m_swidth = sbp->sb_width;
>  	}
>  
>  	return 0;
> @@ -647,16 +678,6 @@ xfs_mountfs(
>  		mp->m_update_sb = true;
>  	}
>  
> -	/*
> -	 * Check if sb_agblocks is aligned at stripe boundary
> -	 * If sb_agblocks is NOT aligned turn off m_dalign since
> -	 * allocator alignment is within an ag, therefore ag has
> -	 * to be aligned at stripe boundary.
> -	 */
> -	error = xfs_update_alignment(mp);
> -	if (error)
> -		goto out;
> -
>  	xfs_alloc_compute_maxlevels(mp);
>  	xfs_bmap_compute_maxlevels(mp, XFS_DATA_FORK);
>  	xfs_bmap_compute_maxlevels(mp, XFS_ATTR_FORK);
> @@ -664,6 +685,17 @@ xfs_mountfs(
>  	xfs_rmapbt_compute_maxlevels(mp);
>  	xfs_refcountbt_compute_maxlevels(mp);
>  
> +	/*
> +	 * Check if sb_agblocks is aligned at stripe boundary.  If sb_agblocks
> +	 * is NOT aligned turn off m_dalign since allocator alignment is within
> +	 * an ag, therefore ag has to be aligned at stripe boundary.  Note that
> +	 * we must compute the free space and rmap btree geometry before doing
> +	 * this.
> +	 */
> +	error = xfs_update_alignment(mp);
> +	if (error)
> +		goto out;
> +
>  	/* enable fail_at_unmount as default */
>  	mp->m_fail_unmount = true;
>  
> diff --git a/fs/xfs/xfs_trace.h b/fs/xfs/xfs_trace.h
> index c13bb3655e48..a86be7f807ee 100644
> --- a/fs/xfs/xfs_trace.h
> +++ b/fs/xfs/xfs_trace.h
> @@ -3573,6 +3573,27 @@ DEFINE_KMEM_EVENT(kmem_alloc_large);
>  DEFINE_KMEM_EVENT(kmem_realloc);
>  DEFINE_KMEM_EVENT(kmem_zone_alloc);
>  
> +TRACE_EVENT(xfs_check_new_dalign,
> +	TP_PROTO(struct xfs_mount *mp, int new_dalign, xfs_ino_t calc_rootino),
> +	TP_ARGS(mp, new_dalign, calc_rootino),
> +	TP_STRUCT__entry(
> +		__field(dev_t, dev)
> +		__field(int, new_dalign)
> +		__field(xfs_ino_t, sb_rootino)
> +		__field(xfs_ino_t, calc_rootino)
> +	),
> +	TP_fast_assign(
> +		__entry->dev = mp->m_super->s_dev;
> +		__entry->new_dalign = new_dalign;
> +		__entry->sb_rootino = mp->m_sb.sb_rootino;
> +		__entry->calc_rootino = calc_rootino;
> +	),
> +	TP_printk("dev %d:%d new_dalign %d sb_rootino %llu calc_rootino %llu",
> +		  MAJOR(__entry->dev), MINOR(__entry->dev),
> +		  __entry->new_dalign, __entry->sb_rootino,
> +		  __entry->calc_rootino)
> +)
> +
>  #endif /* _TRACE_XFS_H */
>  
>  #undef TRACE_INCLUDE_PATH
>