Re: [PATCH 3/3] xfs: don't commit sunit/swidth updates to disk if that would cause repair failures

Brian Foster
2019-12-19T13:21:42Z

On Wed, Dec 18, 2019 at 11:37:41AM -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>
> ---
> fs/xfs/libxfs/xfs_ialloc.c | 70 ++++++++++++++++++++++++++++++++++++++++++++
> fs/xfs/libxfs/xfs_ialloc.h | 1 +
> fs/xfs/xfs_mount.c | 45 ++++++++++++++++++++++++++++
> fs/xfs/xfs_trace.h | 21 +++++++++++++
> 4 files changed, 136 insertions(+), 1 deletion(-)
>
>
> diff --git a/fs/xfs/libxfs/xfs_ialloc.c b/fs/xfs/libxfs/xfs_ialloc.c
> index 988cde7744e6..eeec7c8d93fd 100644
> --- a/fs/xfs/libxfs/xfs_ialloc.c
> +++ b/fs/xfs/libxfs/xfs_ialloc.c
> @@ -2909,3 +2909,73 @@ xfs_ialloc_setup_geometry(
> else
> igeo->ialloc_align = 0;
> }
> +
> +/*
> + * Compute the location of the root directory inode that is laid out by mkfs.
> + * The @sunit parameter will be copied from the superblock if it is negative.
> + */
> +xfs_ino_t
> +xfs_ialloc_calc_rootino(
> + struct xfs_mount *mp,
> + int sunit)
> +{
> + struct xfs_ino_geometry *igeo = M_IGEO(mp);
> + xfs_agblock_t first_bno;
> +
> + if (sunit < 0)
> + sunit = mp->m_sb.sb_unit;

What's the purpose of this check? Can this actually happen?

That question aside, the rest LGTM:

Reviewed-by: Brian Foster <bfoster@redhat.com>

> +
> + /*
> + * Pre-calculate the geometry of AG 0. We know what it looks like
> + * because libxfs knows how to create allocation groups now.
> + *
> + * first_bno is the first block in which mkfs could possibly have
> + * allocated the root directory inode, once we factor in the metadata
> + * that mkfs formats before it. Namely, the four AG headers...
> + */
> + first_bno = howmany(4 * mp->m_sb.sb_sectsize, mp->m_sb.sb_blocksize);
> +
> + /* ...the two free space btree roots... */
> + first_bno += 2;
> +
> + /* ...the inode btree root... */
> + first_bno += 1;
> +
> + /* ...the initial AGFL... */
> + first_bno += xfs_alloc_min_freelist(mp, NULL);
> +
> + /* ...the free inode btree root... */
> + if (xfs_sb_version_hasfinobt(&mp->m_sb))
> + first_bno++;
> +
> + /* ...the reverse mapping btree root... */
> + if (xfs_sb_version_hasrmapbt(&mp->m_sb))
> + first_bno++;
> +
> + /* ...the reference count btree... */
> + if (xfs_sb_version_hasreflink(&mp->m_sb))
> + first_bno++;
> +
> + /*
> + * ...and the log, if it is allocated in the first allocation group.
> + *
> + * This can happen with filesystems that only have a single
> + * allocation group, or very odd geometries created by old mkfs
> + * versions on very small filesystems.
> + */
> + if (mp->m_sb.sb_logstart &&
> + XFS_FSB_TO_AGNO(mp, mp->m_sb.sb_logstart) == 0)
> + first_bno += mp->m_sb.sb_logblocks;
> +
> + /*
> + * Now round first_bno up to whatever allocation alignment is given
> + * by the filesystem or was passed in.
> + */
> + if (xfs_sb_version_hasdalign(&mp->m_sb) && igeo->ialloc_align > 0)
> + first_bno = roundup(first_bno, sunit);
> + else if (xfs_sb_version_hasalign(&mp->m_sb) &&
> + mp->m_sb.sb_inoalignmt > 1)
> + first_bno = roundup(first_bno, mp->m_sb.sb_inoalignmt);
> +
> + return XFS_AGINO_TO_INO(mp, 0, XFS_AGB_TO_AGINO(mp, first_bno));
> +}
> 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
> @@ -152,5 +152,6 @@ int xfs_inobt_insert_rec(struct xfs_btree_cur *cur, uint16_t holemask,
>
> int xfs_ialloc_cluster_alignment(struct xfs_mount *mp);
> void xfs_ialloc_setup_geometry(struct xfs_mount *mp);
> +xfs_ino_t xfs_ialloc_calc_rootino(struct xfs_mount *mp, int sunit);
>
> #endif /* __XFS_IALLOC_H__ */
> diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
> index 3750f0074c74..7f94c6b20920 100644
> --- a/fs/xfs/xfs_mount.c
> +++ b/fs/xfs/xfs_mount.c
> @@ -31,7 +31,7 @@
> #include "xfs_reflink.h"
> #include "xfs_extent_busy.h"
> #include "xfs_health.h"
> -
> +#include "xfs_trace.h"
>
> static DEFINE_MUTEX(xfs_uuid_table_mutex);
> static int xfs_uuid_table_size;
> @@ -359,6 +359,42 @@ xfs_readsb(
> return error;
> }
>
> +/*
> + * If the sunit/swidth change would move the precomputed root inode value, we
> + * must reject the ondisk change because repair will stumble over that.
> + * However, we allow the mount to proceed because we never rejected this
> + * combination before. Returns true to update the sb, false otherwise.
> + */
> +static inline int
> +xfs_check_new_dalign(
> + struct xfs_mount *mp,
> + int new_dalign,
> + bool *update_sb)
> +{
> + struct xfs_sb *sbp = &mp->m_sb;
> + xfs_ino_t calc_ino;
> +
> + calc_ino = xfs_ialloc_calc_rootino(mp, new_dalign);
> + trace_xfs_check_new_dalign(mp, new_dalign, calc_ino);
> +
> + if (sbp->sb_rootino == calc_ino) {
> + *update_sb = true;
> + return 0;
> + }
> +
> + xfs_warn(mp,
> +"Cannot change stripe alignment; would require moving root inode.");
> +
> + /*
> + * XXX: Next time we add a new incompat feature, this should start
> + * returning -EINVAL to fail the mount. Until then, spit out a warning
> + * that we're ignoring the administrator's instructions.
> + */
> + xfs_warn(mp, "Skipping superblock stripe alignment update.");
> + *update_sb = false;
> + return 0;
> +}
> +
> /*
> * If we were provided with new sunit/swidth values as mount options, make sure
> * that they pass basic alignment and superblock feature checks, and convert
> @@ -422,10 +458,17 @@ xfs_update_alignment(
> struct xfs_sb *sbp = &mp->m_sb;
>
> if (mp->m_dalign) {
> + bool update_sb;
> + int error;
> +
> if (sbp->sb_unit == mp->m_dalign &&
> sbp->sb_width == mp->m_swidth)
> return 0;
>
> + error = xfs_check_new_dalign(mp, mp->m_dalign, &update_sb);
> + if (error || !update_sb)
> + return error;
> +
> sbp->sb_unit = mp->m_dalign;
> sbp->sb_width = mp->m_swidth;
> mp->m_update_sb = 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
>