linux-kernel - Re: [PATCH v2 1/7] fault-inject: add support for static keys around fault injection sites

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Date: Tue, 25 Jun 2024 10:08:17 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: Akinobu Mita <akinobu.mita@...il.com>, Christoph Lameter <cl@...ux.com>,
 David Rientjes <rientjes@...gle.com>, Alexei Starovoitov <ast@...nel.org>,
 Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko
 <andrii@...nel.org>, "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>, Anil S
 Keshavamurthy <anil.s.keshavamurthy@...el.com>, "David S. Miller"
 <davem@...emloft.net>, Masami Hiramatsu <mhiramat@...nel.org>, Mark Rutland
 <mark.rutland@....com>, Jiri Olsa <jolsa@...nel.org>, Roman Gushchin
 <roman.gushchin@...ux.dev>, Hyeonggon Yoo <42.hyeyoo@...il.com>,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org, bpf@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/7] fault-inject: add support for static keys around
 fault injection sites

On Thu, 20 Jun 2024 00:48:55 +0200
Vlastimil Babka <vbabka@...e.cz> wrote:

> +static int debugfs_prob_set(void *data, u64 val)
> +{
> +	struct fault_attr *attr = data;
> +
> +	mutex_lock(&probability_mutex);
> +
> +	if (attr->active) {
> +		if (attr->probability != 0 && val == 0) {
> +			static_key_slow_dec(attr->active);
> +		} else if (attr->probability == 0 && val != 0) {
> +			static_key_slow_inc(attr->active);
> +		}
> +	}

So basically the above is testing if val to probability is going from
zero or non-zero. For such cases, I find it less confusing to have:

	if (attr->active) {
		if (!!attr->probability != !!val) {
			if (val)
				static_key_slow_inc(attr->active);
			else
				static_key_slow_dec(attr->active);
		}
	}

This does add a layer of nested ifs, but IMO it's a bit more clear in
what is happening, and it gets rid of the "else if".

Not saying you need to change it. This is more of an FYI.

-- Steve

> +
> +	attr->probability = val;
> +
> +	mutex_unlock(&probability_mutex);
> +
> +	return 0;
> +}