Re: [syzbot] [bpf?] BUG: using smp_processor_id() in preemptible code in bpf_mem_cache_free_rcu

[Edward Adam Davis]

#syz test

diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c
index bd45dda9dc35..11989d32e3f4 100644
--- a/kernel/bpf/memalloc.c
+++ b/kernel/bpf/memalloc.c
@@ -933,7 +933,7 @@ void notrace bpf_mem_free_rcu(struct bpf_mem_alloc *ma, void *ptr)
 	if (WARN_ON_ONCE(idx < 0))
 		return;
 
-	unit_free_rcu(this_cpu_ptr(ma->caches)->cache + idx, ptr);
+	unit_free_rcu(per_cpu_ptr(ma->cache, raw_smp_processor_id()), ptr);
 }
 
 void notrace *bpf_mem_cache_alloc(struct bpf_mem_alloc *ma)