Re: [PATCH v6 bpf-next 2/6] bpf: prevent deadlock from recursive bpf_task_storage_[get|delete]
From: Martin KaFai Lau
Date: Thu Feb 25 2021 - 19:03:26 EST
On Thu, Feb 25, 2021 at 03:43:15PM -0800, Song Liu wrote:
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BPF helpers bpf_task_storage_[get|delete] could hold two locks:
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bpf_local_storage_map_bucket->lock and bpf_local_storage->lock. Calling
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these helpers from fentry/fexit programs on functions in bpf_*_storage.c
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may cause deadlock on either locks.
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Prevent such deadlock with a per cpu counter, bpf_task_storage_busy. We
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need this counter to be global, because the two locks here belong to two
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different objects: bpf_local_storage_map and bpf_local_storage. If we
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pick one of them as the owner of the counter, it is still possible to
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trigger deadlock on the other lock. For example, if bpf_local_storage_map
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owns the counters, it cannot prevent deadlock on bpf_local_storage->lock
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when two maps are used.
Acked-by: Martin KaFai Lau <kafai@xxxxxx>