On Wed, Jan 06, 2021 at 12:41:19PM -0500, Brian Foster wrote:
> xfs_log_sbcount() syncs the superblock specifically to accumulate
> the in-core percpu superblock counters and commit them to disk. This
> is required to maintain filesystem consistency across quiesce
> (freeze, read-only mount/remount) or unmount when lazy superblock
> accounting is enabled because individual transactions do not update
> the superblock directly.
>
> This mechanism works as expected for writable mounts, but
> xfs_log_sbcount() skips the update for read-only mounts. Read-only
> mounts otherwise still allow log recovery and write out an unmount
> record during log quiesce. If a read-only mount performs log
> recovery, it can modify the in-core superblock counters and write an
> unmount record when the filesystem unmounts without ever syncing the
> in-core counters. This leaves the filesystem with a clean log but in
> an inconsistent state with regard to lazy sb counters.
>
> Update xfs_log_sbcount() to use the same logic
> xfs_log_unmount_write() uses to determine when to write an unmount
> record. We can drop the freeze state check because the update is
> already allowed during the freezing process and no context calls
> this function on an already frozen fs. This ensures that lazy
> accounting is always synced before the log is cleaned. Refactor this
> logic into a new helper to distinguish between a writable filesystem
> and a writable log. Specifically, the log is writable unless the
> filesystem is mounted with the norecovery mount option, the
> underlying log device is read-only, or the filesystem is shutdown.
>
> Signed-off-by: Brian Foster <bfoster@xxxxxxxxxx>
> Reviewed-by: Gao Xiang <hsiangkao@xxxxxxxxxx>
Looks good to me,
Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
--D
> ---
> fs/xfs/xfs_log.c | 28 ++++++++++++++++++++--------
> fs/xfs/xfs_log.h | 1 +
> fs/xfs/xfs_mount.c | 3 +--
> 3 files changed, 22 insertions(+), 10 deletions(-)
>
> diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
> index fa2d05e65ff1..b445e63cbc3c 100644
> --- a/fs/xfs/xfs_log.c
> +++ b/fs/xfs/xfs_log.c
> @@ -347,6 +347,25 @@ xlog_tic_add_region(xlog_ticket_t *tic, uint len, uint type)
> tic->t_res_num++;
> }
>
> +bool
> +xfs_log_writable(
> + struct xfs_mount *mp)
> +{
> + /*
> + * Never write to the log on norecovery mounts, if the block device is
> + * read-only, or if the filesystem is shutdown. Read-only mounts still
> + * allow internal writes for log recovery and unmount purposes, so don't
> + * restrict that case here.
> + */
> + if (mp->m_flags & XFS_MOUNT_NORECOVERY)
> + return false;
> + if (xfs_readonly_buftarg(mp->m_log->l_targ))
> + return false;
> + if (XFS_FORCED_SHUTDOWN(mp))
> + return false;
> + return true;
> +}
> +
> /*
> * Replenish the byte reservation required by moving the grant write head.
> */
> @@ -886,15 +905,8 @@ xfs_log_unmount_write(
> {
> struct xlog *log = mp->m_log;
>
> - /*
> - * Don't write out unmount record on norecovery mounts or ro devices.
> - * Or, if we are doing a forced umount (typically because of IO errors).
> - */
> - if (mp->m_flags & XFS_MOUNT_NORECOVERY ||
> - xfs_readonly_buftarg(log->l_targ)) {
> - ASSERT(mp->m_flags & XFS_MOUNT_RDONLY);
> + if (!xfs_log_writable(mp))
> return;
> - }
>
> xfs_log_force(mp, XFS_LOG_SYNC);
>
> diff --git a/fs/xfs/xfs_log.h b/fs/xfs/xfs_log.h
> index 58c3fcbec94a..98c913da7587 100644
> --- a/fs/xfs/xfs_log.h
> +++ b/fs/xfs/xfs_log.h
> @@ -127,6 +127,7 @@ int xfs_log_reserve(struct xfs_mount *mp,
> int xfs_log_regrant(struct xfs_mount *mp, struct xlog_ticket *tic);
> void xfs_log_unmount(struct xfs_mount *mp);
> int xfs_log_force_umount(struct xfs_mount *mp, int logerror);
> +bool xfs_log_writable(struct xfs_mount *mp);
>
> struct xlog_ticket *xfs_log_ticket_get(struct xlog_ticket *ticket);
> void xfs_log_ticket_put(struct xlog_ticket *ticket);
> diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
> index 7110507a2b6b..a62b8a574409 100644
> --- a/fs/xfs/xfs_mount.c
> +++ b/fs/xfs/xfs_mount.c
> @@ -1176,8 +1176,7 @@ xfs_fs_writable(
> int
> xfs_log_sbcount(xfs_mount_t *mp)
> {
> - /* allow this to proceed during the freeze sequence... */
> - if (!xfs_fs_writable(mp, SB_FREEZE_COMPLETE))
> + if (!xfs_log_writable(mp))
> return 0;
>
> /*
> --
> 2.26.2
>
