linux-kernel - Re: [POC] recoverable fault injection

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Message-ID: <CAC5umyibe0tb+HLxx3dbT7gF_nVAAHso1Y0Qb4Q_+y0KNrnvFg@mail.gmail.com>
Date:	Thu, 22 Nov 2012 20:40:31 +0900
From:	Akinobu Mita <akinobu.mita@...il.com>
To:	Johannes Berg <johannes@...solutions.net>
Cc:	linux-kernel@...r.kernel.org, linux-wireless@...r.kernel.org
Subject: Re: [POC] recoverable fault injection

2012/11/22 Johannes Berg <johannes@...solutions.net>:
> This idea has been floating around in my head for a long time now ...
>
> I was thinking: what if we could do fault injection during regular
> testing, at least on those code paths that are not supposed to have side
> effects when they fail? Now obviously this isn't all code paths, and
> many probably erroneously *do* have side effects even if they're not
> supposed to, but it does apply to a number of code paths.

It sounds interesting. I have never thought of this idea.

> So I decided to play with this, and the result it the patch below. It
> adds a new knob "recoverable-only" to the slab and page_alloc fault
> attributes. If enabled, then a single fault can be injected if the task
> executing it is in a "recoverable section", this is implemented by some
> new fields in struct task_struct and the (very ugly!) macro
> FAULT_INJECT_CALL_RECOVERABLE_FUNCTION.

I suggest introducing a pair of function like:

void fault_recoverable_enable(unsigned long fault_ids);
void fault_recoverable_disable();

fault_recoverable_enable() sets current task's recoverable state to the
value specified with the argument.  fault_recoverable_disable() resets
the recoverable state.

I think this can be more readable than FAULT_INJECT_CALL_RECOVERABLE_FUNCTION
macro.  In case of nl80211_remain_on_channel(), you can just put
them in exit and entrance:

fault_recoverable_enable(FAULT_ATTR_SLAB | FAULT_ATTR_PAGE_ALLOC);
...
fault_recoverable_disable();

return err;
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