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Subject[patch V2 05/20] bpf: Remove recursion prevention from rcu free callback
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>
---
V2: New patch
---
kernel/bpf/hashtab.c | 8 --------
1 file changed, 8 deletions(-)

--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -694,15 +694,7 @@ static void htab_elem_free_rcu(struct rc
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 free_htab_elem(struct bpf_htab *htab, struct htab_elem *l)
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