On 2022-05-21 05:51, Christoph Hellwig wrote:
> 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?
There are a bunch of existing magic numbers in this code. Just before
this hunk there's a if (resync <= 3) and just after the code there's an
if (resync < 3).
There's a comment in md_do_sync() indicating overloaded values for 1 and
2. I can try and turn this into an enum for v2.
Logan
