On Thu, Jul 22, 2021 at 11:53:35AM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@xxxxxxxxxx>
>
> Before waiting on a iclog in xfs_log_force_lsn(), we don't check to
> see if the iclog has already been completed and the contents on
> stable storage. We check for completed iclogs in xfs_log_force(), so
> we should do the same thing for xfs_log_force_lsn().
>
> This fixed some random up-to-30s pauses seen in unmounting
> filesystems in some tests. A log force ends up waiting on completed
> iclog, and that doesn't then get flushed (and hence the log force
> get completed) until the background log worker issues a log force
> that flushes the iclog in question. Then the unmount unblocks and
> continues.
>
> Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
Heh.
Reviewed-by: Darrick J. Wong <djwong@xxxxxxxxxx>
--D
> ---
> fs/xfs/xfs_log.c | 47 +++++++++++++++++++++++++++++++++++++----------
> 1 file changed, 37 insertions(+), 10 deletions(-)
>
> diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
> index 7da42c0656e3..baee9871cd65 100644
> --- a/fs/xfs/xfs_log.c
> +++ b/fs/xfs/xfs_log.c
> @@ -3147,6 +3147,35 @@ xlog_state_switch_iclogs(
> log->l_iclog = iclog->ic_next;
> }
>
> +/*
> + * Force the iclog to disk and check if the iclog has been completed before
> + * xlog_force_iclog() returns. This can happen on synchronous (e.g.
> + * pmem) or fast async storage because we drop the icloglock to issue the IO.
> + * If completion has already occurred, tell the caller so that it can avoid an
> + * unnecessary wait on the iclog.
> + */
> +static int
> +xlog_force_and_check_iclog(
> + struct xlog_in_core *iclog,
> + bool *completed)
> +{
> + xfs_lsn_t lsn = be64_to_cpu(iclog->ic_header.h_lsn);
> + int error;
> +
> + *completed = false;
> + error = xlog_force_iclog(iclog);
> + if (error)
> + return error;
> +
> + /*
> + * If the iclog has already been completed and reused the header LSN
> + * will have been rewritten by completion
> + */
> + if (be64_to_cpu(iclog->ic_header.h_lsn) != lsn)
> + *completed = true;
> + return 0;
> +}
> +
> /*
> * Write out all data in the in-core log as of this exact moment in time.
> *
> @@ -3181,7 +3210,6 @@ xfs_log_force(
> {
> struct xlog *log = mp->m_log;
> struct xlog_in_core *iclog;
> - xfs_lsn_t lsn;
>
> XFS_STATS_INC(mp, xs_log_force);
> trace_xfs_log_force(mp, 0, _RET_IP_);
> @@ -3210,15 +3238,11 @@ xfs_log_force(
> } else if (iclog->ic_state == XLOG_STATE_ACTIVE) {
> if (atomic_read(&iclog->ic_refcnt) == 0) {
> /* We have exclusive access to this iclog. */
> - lsn = be64_to_cpu(iclog->ic_header.h_lsn);
> - if (xlog_force_iclog(iclog))
> + bool completed;
> +
> + if (xlog_force_and_check_iclog(iclog, &completed))
> goto out_error;
> - /*
> - * If the iclog has already been completed and reused
> - * the header LSN will have been rewritten. Don't wait
> - * on these iclogs that contain future modifications.
> - */
> - if (be64_to_cpu(iclog->ic_header.h_lsn) != lsn)
> + if (completed)
> goto out_unlock;
> } else {
> /*
> @@ -3258,6 +3282,7 @@ xlog_force_lsn(
> bool already_slept)
> {
> struct xlog_in_core *iclog;
> + bool completed;
>
> spin_lock(&log->l_icloglock);
> iclog = log->l_iclog;
> @@ -3295,10 +3320,12 @@ xlog_force_lsn(
> &log->l_icloglock);
> return -EAGAIN;
> }
> - if (xlog_force_iclog(iclog))
> + if (xlog_force_and_check_iclog(iclog, &completed))
> goto out_error;
> if (log_flushed)
> *log_flushed = 1;
> + if (completed)
> + goto out_unlock;
> break;
> case XLOG_STATE_WANT_SYNC:
> /*
> --
> 2.31.1
>
