Re: [PATCH] fix build failure when compiling without TRACE_IRQFLAGS_SUPPORT

[Paul Mundt <lethal@linux-sh.org>]

On Fri, Sep 05, 2008 at 08:33:08AM +0200, Giuseppe CAVALLARO wrote:
> Hi All,
> playing with the kernel configuration we noticed that the
> kernel doesn't build if TRACE_IRQFLAGS_SUPPORT is
> forced off. So this patch just fixes it.
> 
> Anyway, we are wondering why it's not possible to disable
> this option from Kconfig.
> Reading the Documentation/irqflags-tracing.txt, this option is
> "needed for CONFIG_PROVE_SPIN_LOCKING and
> CONFIG_PROVE_RW_LOCKING to be offered by the generic
> lock debugging code."
> But we cannot find any references to PROVE_RW_LOCKING etc.
> May be removed?
> 
Have you noticed this problem on non-sh platforms also? If so, you should
resend this patch to linux-kernel with the linux-sh list CCed.

The config dependencies are a bit of a mess, but it's all quite
functional. CONFIG_PROVE_RW_LOCKING is bogus though, it's actually
CONFIG_PROVE_LOCKING. Anyways, take a look at lib/Kconfig.debug and it
should all be pretty obvious.

TRACE_IRQFLAGS_SUPPORT is used by quite a lot of things, lockdep, lock
stat, preempt debug, etc. You really do _not_ want to disable this
option, especially as it is a _support_ option, not a functional one.

CONFIG_TRACE_IRQFLAGS itself is what introduces extra overhead, and while
this depends on TRACE_IRQFLAGS_SUPPORT, it also has a dependency on
DEBUG_KERNEL. Thus, you will never see any of this stuff with kernel
debugging disabled. Most of this stuff is hidden away from the user in
Kconfig for a good reason :-)