From: Thomas Gleixner tglx@linutronix.de
[ Upstream commit 8a37963c7ac9ecb7f86f8ebda020e3f8d6d7b8a0 ]
If an element is freed via RCU then recursion into BPF instrumentation functions is not a concern. The element is already detached from the map and the RCU callback does not hold any locks on which a kprobe, perf event or tracepoint attached BPF program could deadlock.
Signed-off-by: Thomas Gleixner tglx@linutronix.de Signed-off-by: Alexei Starovoitov ast@kernel.org Link: https://lore.kernel.org/bpf/20200224145643.259118710@linutronix.de Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/bpf/hashtab.c | 8 -------- 1 file changed, 8 deletions(-)
diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c index 039d64b1bfb7d..728ffec52cf36 100644 --- a/kernel/bpf/hashtab.c +++ b/kernel/bpf/hashtab.c @@ -664,15 +664,7 @@ static void htab_elem_free_rcu(struct rcu_head *head) struct htab_elem *l = container_of(head, struct htab_elem, rcu); struct bpf_htab *htab = l->htab;
- /* must increment bpf_prog_active to avoid kprobe+bpf triggering while - * we're calling kfree, otherwise deadlock is possible if kprobes - * are placed somewhere inside of slub - */ - preempt_disable(); - __this_cpu_inc(bpf_prog_active); htab_elem_free(htab, l); - __this_cpu_dec(bpf_prog_active); - preempt_enable(); }
static void htab_put_fd_value(struct bpf_htab *htab, struct htab_elem *l)