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    Subject[patch V3 08/22] 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
    @@ -706,15 +706,7 @@ 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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