netdev - Re: [PATCH v4 bpf-next 07/14] bpf: Change bpf_mem

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Date: Thu, 6 Jul 2023 20:55:38 +0800
From: Hou Tao <houtao@...weicloud.com>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: tj@...nel.org, rcu@...r.kernel.org, netdev@...r.kernel.org,
 bpf@...r.kernel.org, kernel-team@...com, daniel@...earbox.net,
 andrii@...nel.org, void@...ifault.com, paulmck@...nel.org
Subject: Re: [PATCH v4 bpf-next 07/14] bpf: Change bpf_mem_cache draining
 process.

On 7/6/2023 11:34 AM, Alexei Starovoitov wrote:
> From: Alexei Starovoitov <ast@...nel.org>
>
> The next patch will introduce cross-cpu llist access and existing
> irq_work_sync() + drain_mem_cache() + rcu_barrier_tasks_trace() mechanism will
> not be enough, since irq_work_sync() + drain_mem_cache() on cpu A won't
> guarantee that llist on cpu A are empty. The free_bulk() on cpu B might add
> objects back to llist of cpu A. Add 'bool draining' flag.
> The modified sequence looks like:
> for_each_cpu:
>   WRITE_ONCE(c->draining, true); // do_call_rcu_ttrace() won't be doing call_rcu() any more
>   irq_work_sync(); // wait for irq_work callback (free_bulk) to finish
>   drain_mem_cache(); // free all objects
> rcu_barrier_tasks_trace(); // wait for RCU callbacks to execute
>
> Signed-off-by: Alexei Starovoitov <ast@...nel.org>

Acked-by: Hou Tao <houtao1@...wei.com>