[PATCH bpf-next] bpf/bpf_lru_list: make bpf_percpu_lru_pop_free safe in NMI

[Priya Bala Govindasamy <pgovind2@xxxxxxx>]

bpf_percpu_lru_pop_free uses raw_spin_lock_irqsave. This function is
used by htab_percpu_lru_map_update_elem() which can be called from an
NMI. A deadlock can happen if a bpf program holding the lock is
interrupted by the same program in NMI. Use raw_spin_trylock_irqsave if
in NMI.

Fixes: 961578b63474 (bpf: Add percpu LRU list)
Signed-off-by: Priya Bala Govindasamy <pgovind2@xxxxxxx>
Signed-off-by: Amery Hung <ameryhung@xxxxxxxxx>
---
 kernel/bpf/bpf_lru_list.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/bpf_lru_list.c b/kernel/bpf/bpf_lru_list.c
index 3dabdd137d10..c4a9e861369b 100644
--- a/kernel/bpf/bpf_lru_list.c
+++ b/kernel/bpf/bpf_lru_list.c
@@ -412,7 +412,12 @@ static struct bpf_lru_node
*bpf_percpu_lru_pop_free(struct bpf_lru *lru,

        l = per_cpu_ptr(lru->percpu_lru, cpu);

-       raw_spin_lock_irqsave(&l->lock, flags);
+       if (in_nmi()) {
+               if (!raw_spin_trylock_irqsave(&l->lock, flags))
+                       return NULL;
+       } else {
+               raw_spin_lock_irqsave(&l->lock, flags);
+       }

        __bpf_lru_list_rotate(lru, l);