linux-kernel - Re: [PATCH v4] lockdep: check that no locks held at freeze time

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Message-ID: <CACBanvpa9tg9pTAaTqSkN35-=6EQ53HGumNFM9S9fmcmPGcMjw@mail.gmail.com>
Date:	Wed, 20 Feb 2013 19:19:08 -0800
From:	Mandeep Singh Baines <msb@...omium.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, Oleg Nesterov <oleg@...hat.com>,
	Tejun Heo <tj@...nel.org>, "Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: [PATCH v4] lockdep: check that no locks held at freeze time

On Wed, Feb 20, 2013 at 4:42 PM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
> On Wed, 20 Feb 2013 16:28:07 -0800
> Mandeep Singh Baines <msb@...omium.org> wrote:
>
>> > Backtraces aren't *that* bad.  We'll easily be able to tell which of
>> > the two callsites triggered the trace.
>> >
>>
>> Let's say there was a try_to_freeze() that got inlined indirectly
>> (multiple levels of inline) into do_exit. Wouldn't the backtraces for
>> the regular exit check and the try_to_freeze check be identical except
>> for the offset (do_exit+0x45 versus do_exit+0x88)? So unless you had
>> an object file you wouldn't know which check you hit.
>
> Mutter.  Spose so.  Vaguely possible.  Yes, if we want to avoid a
> wont-happen, use __FILE__ and __LINE__.  Or, probably more sanely,
> __func__.
>

Fair enough. I'll avoid using a macro unless/until its actually needed.

Regards,
Mandeep

> Or uninline try_to_freeze().  If anything's calling that at high
> frequency, we have a problem.  And given the number of callsites,
> getting it into icache might result in a faster kernel...
>
> (Someone needs to teach __might_sleep() about __ratelimit())
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