On Thu, May 19, 2022 at 01:13:10PM -0600, Logan Gunthorpe wrote:
> The 07layouts test in mdadm fails on some systems. The failure
> presents itself as the backup file not being removed before the next
> layout is grown into:
>
> mdadm: /dev/md0: cannot create backup file /tmp/md-test-backup:
> File exists
>
> This is because the background mdadm process, which is responsible for
> cleaning up this backup file gets into an infinite loop waiting for
> the reshape to start. mdadm checks the mdstat file if a reshape is
> going and, if it is not, it waits for an event on the file or times
> out in 5 seconds. On faster machines, the reshape may complete before
> the 5 seconds times out, and thus the background mdadm process loops
> waiting for a reshape to start that has already occurred.
>
> mdadm reads the mdstat file to start, but mdstat does not report that the
> reshape has begun, even though it has indeed begun. So the mdstat_wait()
> call (in mdadm) which polls on the mdstat file won't ever return until
> timing out.
>
> The reason mdstat reports the reshape has started is due to an issue
> in status_resync(). recovery_active is subtracted from curr_resync which
> will result in a value of zero for the first chunk of reshaped data, and
> the resulting read will report no reshape in progress.
>
> To fix this, if "resync - recovery_active" is zero: force the value to
> be 4 so the code reports a resync in progress.
>
> Signed-off-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>
> ---
> drivers/md/md.c | 12 ++++++++++--
> 1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index 8273ac5eef06..dbac63c8e35c 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -8022,10 +8022,18 @@ static int status_resync(struct seq_file *seq, struct mddev *mddev)
> if (test_bit(MD_RECOVERY_DONE, &mddev->recovery))
> /* Still cleaning up */
> resync = max_sectors;
> - } else if (resync > max_sectors)
> + } else if (resync > max_sectors) {
> resync = max_sectors;
> - else
> + } else {
> resync -= atomic_read(&mddev->recovery_active);
> + if (!resync) {
> + /*
> + * Resync has started, but if it's zero, ensure
> + * it is still reported, by forcing it to be 4
> + */
> + resync = 4;
Where does this magic 4 come from?
