linux-kernel - Re: [PATCH v2 11/27] ftrace: Allow subops filtering to be modified

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Date: Mon, 3 Jun 2024 11:37:23 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org, Masami
 Hiramatsu <mhiramat@...nel.org>, Mark Rutland <mark.rutland@....com>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Andrew Morton
 <akpm@...ux-foundation.org>, Alexei Starovoitov
 <alexei.starovoitov@...il.com>, Florent Revest <revest@...omium.org>,
 Martin KaFai Lau <martin.lau@...ux.dev>, bpf <bpf@...r.kernel.org>, Sven
 Schnelle <svens@...ux.ibm.com>, Alexei Starovoitov <ast@...nel.org>, Jiri
 Olsa <jolsa@...nel.org>, Arnaldo Carvalho de Melo <acme@...nel.org>, Daniel
 Borkmann <daniel@...earbox.net>, Alan Maguire <alan.maguire@...cle.com>,
 Peter Zijlstra <peterz@...radead.org>, Thomas Gleixner
 <tglx@...utronix.de>, Guo Ren <guoren@...nel.org>
Subject: Re: [PATCH v2 11/27] ftrace: Allow subops filtering to be modified

On Sat, 01 Jun 2024 23:37:55 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

[...]
>  
> +static int ftrace_hash_move_and_update_subops(struct ftrace_ops *subops,
> +					      struct ftrace_hash **orig_subhash,
> +					      struct ftrace_hash *hash,
> +					      int enable)
> +{
> +	struct ftrace_ops *ops = subops->managed;
> +	struct ftrace_hash **orig_hash;
> +	struct ftrace_hash *save_hash;
> +	struct ftrace_hash *new_hash;
> +	int ret;
> +
> +	/* Manager ops can not be subops (yet) */
> +	if (WARN_ON_ONCE(!ops || ops->flags & FTRACE_OPS_FL_SUBOP))
> +		return -EINVAL;

This does return if ops->flags & FTRACE_OPS_FL_SUBOP, but --> (1)

> +
> +	/* Move the new hash over to the subops hash */
> +	save_hash = *orig_subhash;
> +	*orig_subhash = __ftrace_hash_move(hash);
> +	if (!*orig_subhash) {
> +		*orig_subhash = save_hash;
> +		return -ENOMEM;
> +	}
> +
> +	/* Create a new_hash to hold the ops new functions */
> +	if (enable) {
> +		orig_hash = &ops->func_hash->filter_hash;
> +		new_hash = append_hashes(ops);
> +	} else {
> +		orig_hash = &ops->func_hash->notrace_hash;
> +		new_hash = intersect_hashes(ops);
> +	}
> +
> +	/* Move the hash over to the new hash */
> +	ret = ftrace_hash_move_and_update_ops(ops, orig_hash, new_hash, enable);

This also a bit wired to me. maybe we need simple version like

`__ftrace_hash_move_and_update_ops()`

And call it from ftrace_hash_move_and_update_ops() and here?

> +
> +	free_ftrace_hash(new_hash);
> +
> +	if (ret) {
> +		/* Put back the original hash */
> +		free_ftrace_hash_rcu(*orig_subhash);
> +		*orig_subhash = save_hash;
> +	} else {
> +		free_ftrace_hash_rcu(save_hash);
> +	}
> +	return ret;
> +}
> +
> +
>  static u64		ftrace_update_time;
>  unsigned long		ftrace_update_tot_cnt;
>  unsigned long		ftrace_number_of_pages;
> @@ -4770,8 +4823,33 @@ static int ftrace_hash_move_and_update_ops(struct ftrace_ops *ops,
>  {
>  	struct ftrace_ops_hash old_hash_ops;
>  	struct ftrace_hash *old_hash;
> +	struct ftrace_ops *op;
>  	int ret;
>  
> +	if (ops->flags & FTRACE_OPS_FL_SUBOP)
> +		return ftrace_hash_move_and_update_subops(ops, orig_hash, hash, enable);

(1) This calls ftrace_hash_move_and_update_subops() if ops->flags & FTRACE_OPS_FL_SUBOP ?

Thank you,

> +
> +	/*
> +	 * If this ops is not enabled, it could be sharing its filters
> +	 * with a subop. If that's the case, update the subop instead of
> +	 * this ops. Shared filters are only allowed to have one ops set
> +	 * at a time, and if we update the ops that is not enabled,
> +	 * it will not affect subops that share it.
> +	 */
> +	if (!(ops->flags & FTRACE_OPS_FL_ENABLED)) {
> +		/* Check if any other manager subops maps to this hash */
> +		do_for_each_ftrace_op(op, ftrace_ops_list) {
> +			struct ftrace_ops *subops;
> +
> +			list_for_each_entry(subops, &op->subop_list, list) {
> +				if ((subops->flags & FTRACE_OPS_FL_ENABLED) &&
> +				     subops->func_hash == ops->func_hash) {
> +					return ftrace_hash_move_and_update_subops(subops, orig_hash, hash, enable);
> +				}
> +			}
> +		} while_for_each_ftrace_op(op);
> +	}
> +
>  	old_hash = *orig_hash;
>  	old_hash_ops.filter_hash = ops->func_hash->filter_hash;
>  	old_hash_ops.notrace_hash = ops->func_hash->notrace_hash;
> -- 
> 2.43.0
> 
> 


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>