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Subject: Re: [PATCH RESEND bpf-next 1/2] bpf: Reduce the scope of
 rcu_read_lock when updating fd map
Content-Language: en-GB
To: Hou Tao <houtao@huaweicloud.com>, bpf@vger.kernel.org
Cc: Martin KaFai Lau <martin.lau@linux.dev>,
 Alexei Starovoitov <alexei.starovoitov@gmail.com>,
 Andrii Nakryiko <andrii@kernel.org>, Song Liu <song@kernel.org>,
 Hao Luo <haoluo@google.com>, Daniel Borkmann <daniel@iogearbox.net>,
 KP Singh <kpsingh@kernel.org>, Stanislav Fomichev <sdf@google.com>,
 Jiri Olsa <jolsa@kernel.org>, John Fastabend <john.fastabend@gmail.com>,
 houtao1@huawei.com
References: <20231208103357.2637299-1-houtao@huaweicloud.com>
 <20231208103357.2637299-2-houtao@huaweicloud.com>
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From: Yonghong Song <yonghong.song@linux.dev>
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On 12/8/23 2:33 AM, Hou Tao wrote:
> From: Hou Tao <houtao1@huawei.com>
>
> There is no rcu-read-lock requirement for ops->map_fd_get_ptr() or
> ops->map_fd_put_ptr(), so doesn't use rcu-read-lock for these two
> callbacks.
>
> For bpf_fd_array_map_update_elem(), accessing array->ptrs doesn't need
> rcu-read-lock because array->ptrs will not be freed until the map-in-map
> is released. For bpf_fd_htab_map_update_elem(), htab_map_update_elem()
> requires rcu-read-lock to be held, so only use rcu_read_lock() during
> the invocation of htab_map_update_elem().
>
> Signed-off-by: Hou Tao <houtao1@huawei.com>

Acked-by: Yonghong Song <yonghong.song@linux.dev>