linux-kernel - Re: [PATCH 2/2 -mm] fault-injection: lightweight code-coverage maximizer

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Date:	Wed, 29 Nov 2006 11:37:37 +0900
From:	Akinobu Mita <akinobu.mita@...il.com>
To:	Don Mullis <dwm@...r.net>
Cc:	akpm <akpm@...l.org>, lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2 -mm] fault-injection: lightweight code-coverage maximizer

On Tue, Nov 28, 2006 at 12:14:36PM -0800, Don Mullis wrote:
> First, waiting a few seconds for the standard FC-6 daemons to wake up.
> Then, Xemacs and Firefox.  Not tested on SMP.

Is it failslab or fail_page_alloc ?

> > This doesn't maximize code coverage. It makes fault-injector reject
> > any failures which have same stacktrace before.
> 
> Since the volume of (repeated) dumps is greatly reduced, 
> interval/probability can be set more aggressively without crippling
> interaction.  This increases the number of error recovery paths covered
> per unit of wall clock time.
> 

It seems artificial. Injecting failures into slab or page allocator causes
vastly greater range of errors and it should be. I feel what you really
want is new fault capability.

Fault injection is designed be extensible. It's not only for failslab,
fail_page_alloc, and fail_make_request.

If we want to inject errors into try_something() and have own tuning or
setting, we just need to extend fault attribute and define own judging
function,

struct fail_try_something_attr {

	struct gorgeous_tuning tuning;
	struct fail_attr attr;

} = fail_try_something = {
	.attr = FAULT_ATTR_INITIALIZER,
};

static int should_fail_try_something(void *data)
{
	if (tuning_did_clever_decision(&fail_try_something.tuning, data))
		return 0;

	return should_fail(&fail_try_something.attr);
}

Then insert it into try_something()

int try_something(void *data)
{
	if (should_fail_try_something(data))
		return 0;
...
	return 1;
}

Common debugfs entries for fault capabilities will be complicated
soon by pushing new entries for every fault case or pattern.

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