Re: [RFC][PATCH] mm: ifdef out VM_BUG_ON check on PREEMPT_RT_FULL

On Thu, Jul 09, 2015 at 05:07:42PM +0200, Thomas Gleixner wrote:

This all or nothing protection is a real show stopper for RT, so we
try to identify what needs protection against what and then we
annotate those sections with proper scope markers, which turn into RT
friendly constructs at compile time.

The name of the marker in question (event_lock) might not be the best
choice, but that does not invalidate the general usefulness of fine
granular protection scope markers. We certainly need to revisit the
names which we slapped on the particular bits and pieces, and discuss
with the subsystem experts the correctness of the scope markers, but
that's a completely different story.

Actually, I think there was a misunderstanding.  Sebastian's patch did
not include any definition of event_lock, so it looked like this is a
global lock defined by -rt that is simply explicit about being global,
rather than a lock that specifically protects memcg event statistics.

Yeah that doesn't make a lot of sense, thinking more about it.  Sorry.

So localizing these locks for -rt is reasonable, I can see that.  That
being said, does it make sense to have such locking in mainline code?
Is there a concrete plan for process-context interrupt handlers in
mainline?  Because it'd be annoying to maintain fine-grained locking
schemes with explicit lock names in a source tree where it never
amounts to anything more than anonymous cli/sti or preempt toggling.

Maybe I still don't understand what you were proposing for mainline
and what you were proposing as the -rt solution.