Re: [PATCH 3/6] selftests/bpf: libarena: Disable IRQs during allocation

>     selftests/bpf: libarena: Disable IRQs during allocation
>
>     The libarena buddy allocator currently uses arena_spin_lock/unlock
>     to protect its internal data structures in its critical section.
>     These locks disable preemption, but not IRQs. This in turns can cause
>     ABBA deadlocks when an allocation/free operation gets an IRQ while
>     in the critical section, and can only resume after another operation
>     that in turn blocks on the buddy lock. We have concretely seen this
>     with sched_ext schedulers:
>
>     a) Task 1 on CPU A attempts an allocation during initialization,
>     which is done without holding an rq lock. The task takes an IRQ
>     in the middle of the allocation.
>     b) Task 2 on CPU B exits. It attempts to take the buddy allocator
>     lock during its sched-ext state teardown, and blocks on the spinlock.
>     It does so while holding CPU B's rq lock.
>     c) The scheduler run on CPU A and attempts to move tasks from CPU
>     B's rq to CPU A's rq before resuming running Task 1. This requires
>     B's rq lock, which requires Task 2 to take the buddy allocator lock
>     first.
>
>     Fix this by disabling IRQs when taking the buddy lock. We use the
>     already existing arena_spin_[lock_irqsave, unlock_irqrestore] calls
>     for this.
>
>     Signed-off-by: Emil Tsalapatis <[email protected]>

This looks like a bug fix for the buddy allocator's locking. Should this
include:

  Fixes: 86426a28c52d ("selftests/bpf: Add buddy allocator for libarena")


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