linux-kernel - Re: [PATCH bpf-next v5 3/8] bpf: Introduce task open coded iterator kfuncs

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Message-ID: <850f21d0-4bd1-42df-8165-9ae985bb5601@bytedance.com>
Date:   Mon, 16 Oct 2023 16:40:38 +0800
From:   Chuyi Zhou <zhouchuyi@...edance.com>
To:     bpf@...r.kernel.org
Cc:     ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
        martin.lau@...nel.org, tj@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v5 3/8] bpf: Introduce task open coded iterator
 kfuncs



在 2023/10/11 20:08, Chuyi Zhou 写道:
> This patch adds kfuncs bpf_iter_task_{new,next,destroy} which allow
> creation and manipulation of struct bpf_iter_task in open-coded iterator
> style. BPF programs can use these kfuncs or through bpf_for_each macro to
> iterate all processes in the system.
> 
> The API design keep consistent with SEC("iter/task"). bpf_iter_task_new()
> accepts a specific task and iterating type which allows:
> 
> 1. iterating all process in the system(BPF_TASK_ITER_ALL_PROCS)
> 
> 2. iterating all threads in the system(BPF_TASK_ITER_ALL_THREADS)
> 
> 3. iterating all threads of a specific task(BPF_TASK_ITER_PROC_THREADS)
> 
> Signed-off-by: Chuyi Zhou <zhouchuyi@...edance.com>
> ---
>   kernel/bpf/helpers.c                          |  3 +
>   kernel/bpf/task_iter.c                        | 82 +++++++++++++++++++
>   .../testing/selftests/bpf/bpf_experimental.h  |  5 ++
>   3 files changed, 90 insertions(+)
> 
> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index cb24c4a916df..690763751f6e 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -2555,6 +2555,9 @@ BTF_ID_FLAGS(func, bpf_iter_num_destroy, KF_ITER_DESTROY)
>   BTF_ID_FLAGS(func, bpf_iter_css_task_new, KF_ITER_NEW | KF_TRUSTED_ARGS)
>   BTF_ID_FLAGS(func, bpf_iter_css_task_next, KF_ITER_NEXT | KF_RET_NULL)
>   BTF_ID_FLAGS(func, bpf_iter_css_task_destroy, KF_ITER_DESTROY)
> +BTF_ID_FLAGS(func, bpf_iter_task_new, KF_ITER_NEW | KF_TRUSTED_ARGS)
> +BTF_ID_FLAGS(func, bpf_iter_task_next, KF_ITER_NEXT | KF_RET_NULL)
> +BTF_ID_FLAGS(func, bpf_iter_task_destroy, KF_ITER_DESTROY)
>   BTF_ID_FLAGS(func, bpf_dynptr_adjust)
>   BTF_ID_FLAGS(func, bpf_dynptr_is_null)
>   BTF_ID_FLAGS(func, bpf_dynptr_is_rdonly)
> diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
> index 2cfcb4dd8a37..caeddad3d2f1 100644
> --- a/kernel/bpf/task_iter.c
> +++ b/kernel/bpf/task_iter.c
> @@ -856,6 +856,88 @@ __bpf_kfunc void bpf_iter_css_task_destroy(struct bpf_iter_css_task *it)
>   	bpf_mem_free(&bpf_global_ma, kit->css_it);
>   }
>   
> +struct bpf_iter_task {
> +	__u64 __opaque[3];
> +} __attribute__((aligned(8)));
> +
> +struct bpf_iter_task_kern {
> +	struct task_struct *task;
> +	struct task_struct *pos;
> +	unsigned int flags;
> +} __attribute__((aligned(8)));
> +
> +enum {
> +	BPF_TASK_ITER_ALL_PROCS,
> +	BPF_TASK_ITER_ALL_THREADS,
> +	BPF_TASK_ITER_PROC_THREADS
> +};
> +

In next version, I would add the missing __diag_ignore_all for 
-Wmissing-prototypes in Patch2 ~ Patch4 to avoid kernel build warning.

Thanks.

> +__bpf_kfunc int bpf_iter_task_new(struct bpf_iter_task *it,
> +		struct task_struct *task, unsigned int flags)
> +{
> +	struct bpf_iter_task_kern *kit = (void *)it;
> +
> +	BUILD_BUG_ON(sizeof(struct bpf_iter_task_kern) > sizeof(struct bpf_iter_task));
> +	BUILD_BUG_ON(__alignof__(struct bpf_iter_task_kern) !=
> +					__alignof__(struct bpf_iter_task));
> +
> +	kit->task = kit->pos = NULL;
> +	switch (flags) {
> +	case BPF_TASK_ITER_ALL_THREADS:
> +	case BPF_TASK_ITER_ALL_PROCS:
> +	case BPF_TASK_ITER_PROC_THREADS:
> +		break;
> +	default:
> +		return -EINVAL;
> +	}
> +
> +	if (flags == BPF_TASK_ITER_PROC_THREADS)
> +		kit->task = task;
> +	else
> +		kit->task = &init_task;
> +	kit->pos = kit->task;
> +	kit->flags = flags;
> +	return 0;
> +}
> +
> +__bpf_kfunc struct task_struct *bpf_iter_task_next(struct bpf_iter_task *it)
> +{
> +	struct bpf_iter_task_kern *kit = (void *)it;
> +	struct task_struct *pos;
> +	unsigned int flags;
> +
> +	flags = kit->flags;
> +	pos = kit->pos;
> +
> +	if (!pos)
> +		goto out;
> +
> +	if (flags == BPF_TASK_ITER_ALL_PROCS)
> +		goto get_next_task;
> +
> +	kit->pos = next_thread(kit->pos);
> +	if (kit->pos == kit->task) {
> +		if (flags == BPF_TASK_ITER_PROC_THREADS) {
> +			kit->pos = NULL;
> +			goto out;
> +		}
> +	} else
> +		goto out;
> +
> +get_next_task:
> +	kit->pos = next_task(kit->pos);
> +	kit->task = kit->pos;
> +	if (kit->pos == &init_task)
> +		kit->pos = NULL;
> +
> +out:
> +	return pos;
> +}
> +
> +__bpf_kfunc void bpf_iter_task_destroy(struct bpf_iter_task *it)
> +{
> +}
> +
>   DEFINE_PER_CPU(struct mmap_unlock_irq_work, mmap_unlock_work);
>