In the Linux kernel, the following vulnerability has been resolved:
bpf: Fix NMI/tracepoint re-entry deadlock on lru locks
NMI and tracepoint BPF programs can re-enter the per-CPU or global LRU lock that bpf_lru_pop_free()/push_free() already hold on the same CPU, AA-deadlocking. Lockdep reports inconsistent {INITIAL USE} -> {IN-NMI} on &l->lock (syzbot c69a0a2c816716f1e0d5) and possible recursive locking detected on &loc_l->lock (syzbot 18b26edb69b2e19f3b33).
Prior trylock and rqspinlock based fixes (see links) were nacked because compromised on reliability.
This patch converts every LRU lock site to rqspinlock_t and adds a recovery path for some failure windows to avoid node leaks.
Failure recovery:
*_pop_free top-level: return NULL; prealloc_lru_pop() already treats that as no-free-element (-ENOMEM).
Cross-CPU steal: skip the victims locked loc_l, try next CPU.
Post-steal local lock fail: publish stolen node to lockless per-CPU free_llist; next pop on this CPU picks it up.
push_free fail: mark node pending_free=1. __local_list_flush(), __local_list_pop_pending() reclaim the node from pending_list. __bpf_lru_list_shrink_inactive() reclaims the node from inactive list. Nodes from active list are reclaimed by __bpf_lru_list_shrink() or after __bpf_lru_list_rotate_active() demotes it to the inactive.