Fix preemption panic #11346
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Fix preemption panic #11346
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October 19, 2021 13:14
lgfa29
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Nov 15, 2021
Fix a bug where the scheduler may panic when preemption is enabled. The conditions are a bit complicated: A job with higher priority that schedule multiple allocations that preempt other multiple allocations on the same node, due to port/network/device assignments. The cause of the bug is incidental mutation of internal cached data. `RankedNode` computes and cache proposed allocations in https://github.com/hashicorp/nomad/blob/v1.1.6/scheduler/rank.go#L42-L53 . But scheduler then mutates the list to remove pre-emptable allocs in https://github.com/hashicorp/nomad/blob/v1.1.6/scheduler/rank.go#L293-L294, and `RemoveAllocs` mutates and sets the tail of cached slice with `nil`s triggering a nil-pointer derefencing case. I fixed the issue by avoiding the mutation in `RemoveAllocs` - the micro-optimization there doesn't seem necessary. Fixes #11342
lgfa29
pushed a commit
that referenced
this pull request
Nov 15, 2021
Fix a bug where the scheduler may panic when preemption is enabled. The conditions are a bit complicated: A job with higher priority that schedule multiple allocations that preempt other multiple allocations on the same node, due to port/network/device assignments. The cause of the bug is incidental mutation of internal cached data. `RankedNode` computes and cache proposed allocations in https://github.com/hashicorp/nomad/blob/v1.1.6/scheduler/rank.go#L42-L53 . But scheduler then mutates the list to remove pre-emptable allocs in https://github.com/hashicorp/nomad/blob/v1.1.6/scheduler/rank.go#L293-L294, and `RemoveAllocs` mutates and sets the tail of cached slice with `nil`s triggering a nil-pointer derefencing case. I fixed the issue by avoiding the mutation in `RemoveAllocs` - the micro-optimization there doesn't seem necessary. Fixes #11342
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Fix a bug where the scheduler may panic when preemption is enabled. The conditions are a bit complicated:
A job with higher priority that schedule multiple allocations that preempt other multiple allocations on the same node, due to port/network/device assignments.
The cause of the bug is incidental mutation of internal cached data.
RankedNodecomputes and cache proposed allocations in https://github.com/hashicorp/nomad/blob/v1.1.6/scheduler/rank.go#L42-L53 . But scheduler then mutates the list to remove pre-emptable allocs in https://github.com/hashicorp/nomad/blob/v1.1.6/scheduler/rank.go#L293-L294, andRemoveAllocsmutates and sets the tail of cached slice withnils triggering a nil-pointer derefencing case.I fixed the issue by avoiding the mutation in
RemoveAllocs- the micro-optimization there doesn't seem necessary.I've added a test to reproduce the case - it's failing initially in https://app.circleci.com/pipelines/github/hashicorp/nomad/17929/workflows/e2a3a813-351b-40d6-ab78-651de9cf5cae/jobs/178654 .
Fixes #11342