Should we be using CONFIG_PREEMPT_BKL in the Fedora kernel?

[Ingo Molnar]

* Dave Jones <davej at redhat.com> wrote:

> It's crossed my mind to turn it on occasionally in rawhide just to 
> shake out those hard to find bugs.  The thing that's put me off has 
> been that well, we've got enough bugs already without needing to find 
> more right now.

it's on by default in -rt and i havent had a bug triggered by it for 
quite a long time. We had many SMP races triggered by PREEMPT_RT.

part of the reason of PREEMPT_BKL's reliability is because when i did it 
i also wrote debugging infrastructure to catch bugs that would only 
trigger on PREEMPT_BKL=y: the smp_processor_id() debugging code of 
CONFIG_DEBUG_PREEMPT. (and that infrastructure, like lockdep, catches 
bugs before they actually happen, by flagging buggy codepath the first 
time it ever executes)

	Ingo