linux-kernel - Re: [PATCH v18 11/17] fprobe: Rewrite fprobe on function-graph tracer

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Message-ID: <20241101152844.3a589594@gandalf.local.home>
Date: Fri, 1 Nov 2024 15:28:44 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Cc: Alexei Starovoitov <alexei.starovoitov@...il.com>, Florent Revest
 <revest@...omium.org>, linux-trace-kernel@...r.kernel.org, LKML
 <linux-kernel@...r.kernel.org>, Martin KaFai Lau <martin.lau@...ux.dev>,
 bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>, Jiri Olsa
 <jolsa@...nel.org>, Alan Maguire <alan.maguire@...cle.com>, Mark Rutland
 <mark.rutland@....com>, linux-arch@...r.kernel.org, Catalin Marinas
 <catalin.marinas@....com>, Will Deacon <will@...nel.org>, Huacai Chen
 <chenhuacai@...nel.org>, WANG Xuerui <kernel@...0n.name>, Michael Ellerman
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 <christophe.leroy@...roup.eu>, Naveen N Rao <naveen@...nel.org>, Madhavan
 Srinivasan <maddy@...ux.ibm.com>, Paul Walmsley <paul.walmsley@...ive.com>,
 Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>,
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 Alexander Gordeev <agordeev@...ux.ibm.com>, Christian Borntraeger
 <borntraeger@...ux.ibm.com>, Sven Schnelle <svens@...ux.ibm.com>, Thomas
 Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav
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 x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>, Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v18 11/17] fprobe: Rewrite fprobe on function-graph
 tracer

On Sat, 26 Oct 2024 13:37:43 +0900
"Masami Hiramatsu (Google)" <mhiramat@...nel.org> wrote:

> diff --git a/include/linux/fprobe.h b/include/linux/fprobe.h
> index ef609bcca0f9..686b30ce48b4 100644
> --- a/include/linux/fprobe.h
> +++ b/include/linux/fprobe.h
> @@ -5,10 +5,11 @@
>  
>  #include <linux/compiler.h>
>  #include <linux/ftrace.h>
> -#include <linux/rethook.h>
> +#include <linux/rcupdate.h>
> +#include <linux/refcount.h>
> +#include <linux/slab.h>
>  
>  struct fprobe;
> -
>  typedef int (*fprobe_entry_cb)(struct fprobe *fp, unsigned long entry_ip,
>  			       unsigned long ret_ip, struct ftrace_regs *regs,
>  			       void *entry_data);
> @@ -17,35 +18,57 @@ typedef void (*fprobe_exit_cb)(struct fprobe *fp, unsigned long entry_ip,
>  			       unsigned long ret_ip, struct ftrace_regs *regs,
>  			       void *entry_data);
>  
> +/**
> + * strcut fprobe_hlist_node - address based hash list node for fprobe.

      struct

> + *
> + * @hlist: The hlist node for address search hash table.
> + * @addr: The address represented by this.

  What is "this" in the above?

> + * @fp: The fprobe which owns this.
> + */
> +struct fprobe_hlist_node {
> +	struct hlist_node	hlist;
> +	unsigned long		addr;
> +	struct fprobe		*fp;
> +};
> +
> +/**
> + * struct fprobe_hlist - hash list nodes for fprobe.
> + *
> + * @hlist: The hlist node for existence checking hash table.
> + * @rcu: rcu_head for RCU deferred release.
> + * @fp: The fprobe which owns this fprobe_hlist.
> + * @size: The size of @array.
> + * @array: The fprobe_hlist_node for each address to probe.
> + */
> +struct fprobe_hlist {
> +	struct hlist_node		hlist;
> +	struct rcu_head			rcu;
> +	struct fprobe			*fp;
> +	int				size;
> +	struct fprobe_hlist_node	array[];

Should the above have __counted_by(size) ?

-- Steve

> +};
> +
>  /**
>   * struct fprobe - ftrace based probe.
> - * @ops: The ftrace_ops.
> + *
>   * @nmissed: The counter for missing events.
>   * @flags: The status flag.
> - * @rethook: The rethook data structure. (internal data)
>   * @entry_data_size: The private data storage size.
> - * @nr_maxactive: The max number of active functions.
> + * @nr_maxactive: The max number of active functions. (*deprecated)
>   * @entry_handler: The callback function for function entry.
>   * @exit_handler: The callback function for function exit.
> + * @hlist_array: The fprobe_hlist for fprobe search from IP hash table.
>   */
>  struct fprobe {
> -#ifdef CONFIG_FUNCTION_TRACER
> -	/*
> -	 * If CONFIG_FUNCTION_TRACER is not set, CONFIG_FPROBE is disabled too.
> -	 * But user of fprobe may keep embedding the struct fprobe on their own
> -	 * code. To avoid build error, this will keep the fprobe data structure
> -	 * defined here, but remove ftrace_ops data structure.
> -	 */
> -	struct ftrace_ops	ops;
> -#endif
>  	unsigned long		nmissed;
>  	unsigned int		flags;
> -	struct rethook		*rethook;
>  	size_t			entry_data_size;
>  	int			nr_maxactive;
>  
>  	fprobe_entry_cb entry_handler;
>  	fprobe_exit_cb  exit_handler;
> +
> +	struct fprobe_hlist	*hlist_array;
>  };
>