linux-kernel - Re: [PATCH RFC tip/core/rcu 5/6] rcu: Make __kfree

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Date:	Thu, 26 Apr 2012 15:50:45 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jan Engelhardt <jengelh@...ozas.de>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, josh@...htriplett.org,
	niv@...ibm.com, tglx@...utronix.de, rostedt@...dmis.org,
	Valdis.Kletnieks@...edu, dhowells@...hat.com,
	eric.dumazet@...il.com, darren@...art.com, fweisbec@...il.com,
	patches@...aro.org
Subject: Re: [PATCH RFC tip/core/rcu 5/6] rcu: Make __kfree_rcu() less
 dependent on compiler choices

On Thu, 2012-04-26 at 15:29 +0200, Jan Engelhardt wrote:
> On Thursday 2012-04-26 14:48, Peter Zijlstra wrote:
> >On Mon, 2012-04-23 at 09:42 -0700, Paul E. McKenney wrote:
> >> Currently, __kfree_rcu() is implemented as an inline function, and
> >> contains a BUILD_BUG_ON() that malfunctions if __kfree_rcu() is compiled
> >> as an out-of-line function.  Unfortunately, there are compiler settings
> >> (e.g., -O0) that can result in __kfree_rcu() being compiled out of line,
> >> resulting in annoying build breakage.  This commit therefore converts
> >> both __kfree_rcu() and __is_kfree_rcu_offset() from inline functions to
> >> macros to prevent such misbehavior on the part of the compiler.
> >
> >The kernel very explicitly doesn't support being compiled with -O0, so
> >this is a non-issue, I think you can make it work if you add
> >-finline-functions.
> >
> >I'd drop this, either make the entire kernel compile or don't bother.
> 
> It was not originally meant to make the entire kernel compile with -O0,
> but only select modules/.c files.

Same problem, who cares about select modules/.c files? Why should they
have different rules?

> That, or __always_inline just does not always inline.

It does indeed not without -finline-functions.
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