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

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Message-Id: <20130220164257.0905dc45.akpm@linux-foundation.org>
Date:	Wed, 20 Feb 2013 16:42:57 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Mandeep Singh Baines <msb@...omium.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, 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__.

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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