netdev - Re: [PATCH bpf-next] bpf: Call maybe_wait_bpf_programs() only once from generic_map_delete

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Message-Id: <Yg/o4x6rD+oLb4Eu@google.com>
Date:   Fri, 18 Feb 2022 10:43:47 -0800
From:   sdf@...gle.com
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>, bpf <bpf@...r.kernel.org>,
        Brian Vazquez <brianvv@...gle.com>
Subject: Re: [PATCH bpf-next] bpf: Call maybe_wait_bpf_programs() only once
 from generic_map_delete_batch()

On 02/18, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@...gle.com>

> As stated in the comment found in maybe_wait_bpf_programs(),
> the synchronize_rcu() barrier is only needed before returning
> to userspace, not after each deletion in the batch.

> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Stanislav Fomichev <sdf@...gle.com>

Makes sense. Probably a copy-paste from the non-batch case...

Reviewed-by: Stanislav Fomichev <sdf@...gle.com>

> Cc: Brian Vazquez <brianvv@...gle.com>
> ---
>   kernel/bpf/syscall.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)

> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index  
> a72f63d5a7daee057bcec3fa6119aca32e2945f7..9c7a72b65eee0ec8d54d36e2c0ab9ff4962091af  
> 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -1352,7 +1352,6 @@ int generic_map_delete_batch(struct bpf_map *map,
>   		err = map->ops->map_delete_elem(map, key);
>   		rcu_read_unlock();
>   		bpf_enable_instrumentation();
> -		maybe_wait_bpf_programs(map);
>   		if (err)
>   			break;
>   		cond_resched();
> @@ -1361,6 +1360,8 @@ int generic_map_delete_batch(struct bpf_map *map,
>   		err = -EFAULT;

>   	kvfree(key);
> +
> +	maybe_wait_bpf_programs(map);
>   	return err;
>   }

> --
> 2.35.1.473.g83b2b277ed-goog