genirq/cpuhotplug, x86/vector: Prevent vector leak during CPU offline

In the Linux kernel, the following vulnerability has been resolved:

genirq/cpuhotplug, x86/vector: Prevent vector leak during CPU offline

The absence of IRQD_MOVE_PCNTXT prevents immediate effectiveness of

interrupt affinity reconfiguration via procfs. Instead, the change is

deferred until the next instance of the interrupt being triggered on the

original CPU.

When the interrupt next triggers on the original CPU, the new affinity is

enforced within __irq_move_irq(). A vector is allocated from the new CPU,

but the old vector on the original CPU remains and is not immediately

reclaimed. Instead, apicd->move_in_progress is flagged, and the reclaiming

process is delayed until the next trigger of the interrupt on the new CPU.

Upon the subsequent triggering of the interrupt on the new CPU,

irq_complete_move() adds a task to the old CPU's vector_cleanup list if it

remains online. Subsequently, the timer on the old CPU iterates over its

vector_cleanup list, reclaiming old vectors.

However, a rare scenario arises if the old CPU is outgoing before the

interrupt triggers again on the new CPU.

In that case irq_force_complete_move() is not invoked on the outgoing CPU

to reclaim the old apicd->prev_vector because the interrupt isn't currently

affine to the outgoing CPU, and irq_needs_fixup() returns false. Even

though __vector_schedule_cleanup() is later called on the new CPU, it

doesn't reclaim apicd->prev_vector; instead, it simply resets both

apicd->move_in_progress and apicd->prev_vector to 0.

As a result, the vector remains unreclaimed in vector_matrix, leading to a

CPU vector leak.

To address this issue, move the invocation of irq_force_complete_move()

before the irq_needs_fixup() call to reclaim apicd->prev_vector, if the

interrupt is currently or used to be affine to the outgoing CPU.

Additionally, reclaim the vector in __vector_schedule_cleanup() as well,

following a warning message, although theoretically it should never see

apicd->move_in_progress with apicd->prev_cpu pointing to an offline CPU.