When calculating the score in the `SpreadIterator`, the score boost is
proportional to the difference between the current and desired count. But when
there are implicit spread targets, the current count is the sum of the possible
implicit targets, which results in incorrect scoring unless there's only one
implicit target.
This changeset updates the `propertySet` struct to accept a set of explicit
target values so it can detect when a property value falls into the implicit set
and should be combined with other implicit values.
Fixes: #11823
When spread targets have a percent value of zero it's possible for them to
return -Inf scoring because of a float divide by zero. This is very hard for
operators to debug because the string "-Inf" is returned in the API and that
breaks the presentation of debugging data.
Most scoring iterators are bracketed to -1/+1, but spread iterators do not so
that they can handle greatly unbalanced scoring so we can't simply return a -1
score without generating a score that might be greater than the negative scores
set by other spread targets. Instead, track the lowest-seen spread boost and use
that as the spread boost for any cases where we'd divide by zero.
Fixes: #8863
The spread iterator can panic when processing an evaluation, resulting
in an unrecoverable state in the cluster. Whenever a panicked server
restarts and quorum is restored, the next server to dequeue the
evaluation will panic.
To trigger this state:
* The job must have `max_parallel = 0` and a `canary >= 1`.
* The job must not have a `spread` block.
* The job must have a previous version.
* The previous version must have a `spread` block and at least one
failed allocation.
In this scenario, the desired changes include `(place 1+) (stop
1+), (ignore n) (canary 1)`. Before the scheduler can place the canary
allocation, it tries to find out which allocations can be
stopped. This passes back through the stack so that we can determine
previous-node penalties, etc. We call `SetJob` on the stack with the
previous version of the job, which will include assessing the `spread`
block (even though the results are unused). The task group spread info
state from that pass through the spread iterator is not reset when we
call `SetJob` again. When the new job version iterates over the
`groupPropertySets`, it will get an empty `spreadAttributeMap`,
resulting in an unexpected nil pointer dereference.
This changeset resets the spread iterator internal state when setting
the job, logging with a bypass around the bug in case we hit similar
cases, and a test that panics the scheduler without the patch.
