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FIX #7693: concurrent task execution: fixed dereference of NULL #7694

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FIX #7693: concurrent task execution: fixed dereference of NULL #7694

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6 changes: 5 additions & 1 deletion src/backend/distributed/utils/background_jobs.c
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Original file line number Diff line number Diff line change
Expand Up @@ -706,8 +706,12 @@ TaskConcurrentCancelCheck(TaskExecutionContext *taskExecutionContext)
BackgroundExecutorHashEntry *handleEntry = taskExecutionContext->handleEntry;
BackgroundTask *task = GetBackgroundTaskByTaskId(handleEntry->taskid);
taskExecutionContext->task = task;
if (!task)
{
ereport(ERROR, (errmsg("unexpected missing task id: %ld", handleEntry->taskid)));
}
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You message is not very helpful.

See around line 300 a similar pattern, here patched:

		if (!task)
		{
			ereport(ERROR, (errmsg("no task found with taskid: %ld", handleEntry->taskid)));
		}

Also I suggest to move your patch one line up (before the assignment).

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I wonder if the error message should not be more strong: 'unexpected missing task id: ...;'

Maybe an Assert() given "task" is always expected to be set....

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ereport(ERROR, ...) doesn't return control

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I'm unsure what Citus guidelines are here but I don't think task is ever supposed to be NULL in this function.
That's why maybe an Assert() and not an ereport(ERROR)...

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I'm not sure whether the use of the "assert" is more appropriate, but the ereport(ERROR) is a normal shutdown in the event of errors.


if (!task || task->status == BACKGROUND_TASK_STATUS_CANCELLING)
if (task->status == BACKGROUND_TASK_STATUS_CANCELLING)
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that's a bit of a trouble, in the "else" part too it depends on task being set.

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@ProjectMutilation ProjectMutilation Oct 8, 2024 •
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if exit the function earlier, it will not be trouble

{
/*
* being in that step means that a concurrent cancel or removal happened. we should
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