[Bugfix] Fix for V1 priority scheduling crashes at preemption

[Hanchenli]

fix #23347

Purpose

This PR is to fix for #23347. The bug is due to that when requests are evicted due to low priority and not enough KV space, scheduled_running_reqs are not updated. This PR adds the line to update scheduled_running_reqs and an example test case for scheduler from #23346 .

Test Plan

Test Result

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[gemini-code-assist]

Code Review

This pull request addresses a crash in priority scheduling during preemption by updating the scheduled_running_reqs list. The fix is correct in principle, and the accompanying test case is a valuable addition for verifying this scenario. However, the implementation of the fix in vllm/v1/core/sched/scheduler.py has a flaw that could lead to a ValueError, as it attempts to remove an item from a list without first verifying its presence. This could cause a crash under certain conditions, which I've detailed in a specific comment.

[gemini-code-assist]

This line can cause a ValueError if preempted_req has not been scheduled yet in the current schedule() call, and is therefore not present in scheduled_running_reqs. This can happen if a request being processed triggers its own preemption, or preempts another request that hasn't been processed yet in the current scheduling iteration.

To prevent a crash, you should check if the request is in the list before attempting to remove it.

Suggested change

	scheduled_running_reqs.remove(preempted_req)
	if preempted_req in scheduled_running_reqs:
	scheduled_running_reqs.remove(preempted_req)

[heheda12345]

@Hanchenli I think this make sense. Can you double check?

[Hanchenli]

@heheda12345 Hi, I think this makes sense. I just updated.

[heheda12345]

LGTM! Thanks for the fix.