B4/lru map spin#12134
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Signed-off-by: Mykyta Yatsenko <yatsenko@meta.com>
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{
"series": {
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"change-id": "20260519-lru_map_spin-8e20dabbf460",
"prefixes": []
}
}
Perf-event BPF programs running in NMI can re-enter the per-CPU
loc_l->lock (and the global lru_list lock) that bpf_lru_pop_free()
already holds in syscall context on the same CPU. Lockdep reports
"inconsistent {INITIAL USE} -> {IN-NMI} usage" at bpf_lru_pop_free,
and a real AA deadlock is possible.
Mirror hashtab's fix: switch both locks to rqspinlock_t so the NMI
acquirer sees -EDEADLK from the slow-path AA check and bails. Pop
paths return NULL (same as OOM); push paths skip the move (the node
stays in the preallocated pool until map destroy).
Signed-off-by: Mykyta Yatsenko <yatsenko@meta.com>
Reproduces the loc_l->lock NMI re-entry that lockdep flagged on the
LRU hash map. Pins to CPU 0, attaches a perf_event BPF prog that
updates an LRU map from NMI, and hammers the same map from
userspace. On an unpatched kernel with PROVE_LOCKING this fires the
"inconsistent {INITIAL USE} -> {IN-NMI}" splat within a second.
Marked serial_ because CPU pinning plus a high-rate HW perf event
would perturb parallel tests.
Signed-off-by: Mykyta Yatsenko <yatsenko@meta.com>
AI reviewed your patch. Please fix the bug or email reply why it's not a bug. In-Reply-To-Subject: |
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