linux-kernel - Re: [PATCH 0/8] drop if around WARN

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Message-ID: <CA+1xoqd6TZDsFqtcZuX9A7SOcRfvoZuv5A4wY5bkyGwPJjSF-g@mail.gmail.com>
Date:	Sun, 4 Nov 2012 21:47:41 -0500
From:	Sasha Levin <levinsasha928@...il.com>
To:	Julia Lawall <julia.lawall@...6.fr>
Cc:	linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH 0/8] drop if around WARN_ON

On Sun, Nov 4, 2012 at 11:16 AM, Julia Lawall <julia.lawall@...6.fr> wrote:
> I didn't change any cases where the if test contains a function call.  The
> current definitions of WARN_ON seem to always evaluate the condition
> expression, but I was worried that that might not always be the case.  And
> calling a function (the ones I remember were some kinds of print functions)
> seems like something one might not want buried in the argument of a
> debugging macro.

Makes sense.

> WARN_ON_SMP is just WARN_ON if CONFIG_SMP is true, but it is just 0
> otherwise.  So in that case it seems important to check that one is not
> throwing away something important.

Yup, we just need to make sure that the expression being evaluated doesn't
have side-effects.

> I remember working on the BUG_ON case several years ago, and other people
> worked on it too, but I guess some are still there...  The current
> definitions of BUG_ON seem to keep the condition, but there are quite a few
> specialized definitions, so someone at some point might make a version that
> does not have that property.

It makes sense to keep an eye for such things when converting code. I
also don't think we'll get to see a version of BUG_ON which doesn't
evaluate the expression since the kernel already has more than enough
BUG_ONs that assume the expression will be evaluated:

BUG_ON(HYPERVISOR_callback_op(CALLBACKOP_register, &event));
BUG_ON(gpiochip_add(&gemini_gpio_chip));
BUG_ON(clocksource_register_hz(&sirfsoc_clocksource, CLOCK_TICK_RATE));
BUG_ON(gpio_request(ZOOM2_HEADSET_MUX_GPIO, "hs_mux") < 0);

And so on, so we're probably safe converting to BUG_ON even if the
condition is a function, as long as it doesn't create a long and
complicated BUG_ON() ofcourse.


Thanks,
Sasha
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