linux-kernel - Re: [PATCH bpf-next v1 4/9] bpf: Introduce sleepable tracepoints

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Date:   Wed, 2 Mar 2022 13:23:35 -0800
From:   Yonghong Song <yhs@...com>
To:     Hao Luo <haoluo@...gle.com>, Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Cc:     Martin KaFai Lau <kafai@...com>, Song Liu <songliubraving@...com>,
        KP Singh <kpsingh@...nel.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Joe Burton <jevburton.kernel@...il.com>,
        Tejun Heo <tj@...nel.org>, joshdon@...gle.com, sdf@...gle.com,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v1 4/9] bpf: Introduce sleepable tracepoints



On 2/25/22 3:43 PM, Hao Luo wrote:
> Add a new type of bpf tracepoints: sleepable tracepoints, which allows
> the handler to make calls that may sleep. With sleepable tracepoints, a
> set of syscall helpers (which may sleep) may also be called from
> sleepable tracepoints.

There are some old discussions on sleepable tracepoints, maybe
worthwhile to take a look.

https://lore.kernel.org/bpf/20210218222125.46565-5-mjeanson@efficios.com/T/

> 
> In the following patches, we will whitelist some tracepoints to be
> sleepable.
> 
> Signed-off-by: Hao Luo <haoluo@...gle.com>
> ---
>   include/linux/bpf.h             | 10 +++++++-
>   include/linux/tracepoint-defs.h |  1 +
>   include/trace/bpf_probe.h       | 22 ++++++++++++++----
>   kernel/bpf/syscall.c            | 41 +++++++++++++++++++++++----------
>   kernel/trace/bpf_trace.c        |  5 ++++
>   5 files changed, 61 insertions(+), 18 deletions(-)
> 
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index c36eeced3838..759ade7b24b3 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1810,6 +1810,9 @@ struct bpf_prog *bpf_prog_by_id(u32 id);
>   struct bpf_link *bpf_link_by_id(u32 id);
>   
>   const struct bpf_func_proto *bpf_base_func_proto(enum bpf_func_id func_id);
> +const struct bpf_func_proto *
> +tracing_prog_syscall_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog);
> +
>   void bpf_task_storage_free(struct task_struct *task);
>   bool bpf_prog_has_kfunc_call(const struct bpf_prog *prog);
>   const struct btf_func_model *
> @@ -1822,7 +1825,6 @@ struct bpf_core_ctx {
>   
>   int bpf_core_apply(struct bpf_core_ctx *ctx, const struct bpf_core_relo *relo,
>   		   int relo_idx, void *insn);
> -
>   #else /* !CONFIG_BPF_SYSCALL */
>   static inline struct bpf_prog *bpf_prog_get(u32 ufd)
>   {
> @@ -2011,6 +2013,12 @@ bpf_base_func_proto(enum bpf_func_id func_id)
>   	return NULL;
>   }
>   
> +static inline struct bpf_func_proto *
> +tracing_prog_syscall_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
> +{
> +	return NULL;
> +}
> +
>   static inline void bpf_task_storage_free(struct task_struct *task)
>   {
>   }
> diff --git a/include/linux/tracepoint-defs.h b/include/linux/tracepoint-defs.h
> index e7c2276be33e..c73c7ab3680e 100644
> --- a/include/linux/tracepoint-defs.h
> +++ b/include/linux/tracepoint-defs.h
> @@ -51,6 +51,7 @@ struct bpf_raw_event_map {
>   	void			*bpf_func;
>   	u32			num_args;
>   	u32			writable_size;
> +	u32			sleepable;
>   } __aligned(32);
>   
>   /*
[...]