Re: [Ksummit-discuss] [MAINTAINERS SUMMIT] & [TECH TOPIC] Improve regression tracking

On Wed, 2017-07-05 at 10:56 -0400, Steven Rostedt wrote:

On Wed, 05 Jul 2017 07:50:28 -0700
James Bottomley [off-list ref] wrote:

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On Wed, 2017-07-05 at 10:36 -0400, Steven Rostedt wrote:

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On Wed, 5 Jul 2017 15:33:41 +0100
Mark Brown [off-list ref] wrote:
  

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On Wed, Jul 05, 2017 at 04:06:07PM +0200, Greg KH wrote:
  

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I don't mean to poo-poo the idea, but please realize that
around 75% of the kernel is hardware/arch support, so that
means that 75% of the changes/fixes deal with hardware things
(yes, change is in direct correlation to size of the codebase
in the tree, strange but true).    

Then add in all the fixes for concurrency/locking issues and so
on that're hard to reliably reproduce as well...  

All tests should be run with lockdep enabled ;-)  Which a
surprising few developers appear to do :-p  

Lockdep checks the locking hierarchies and makes assumptions about
them which it then validates ... it doesn't tell you if the data
you think

We should probably look at adding infrastructure that helps in that.
RCU already has a lot of there to help know if data is being
protected by RCU or not.

Hmm, maybe we could add a __rcu like type that we can associate
protected data with, where a config can associate access to a
variable with a lock being held?

That's about 10x more complex than the releases/acquires/must_hold
annotation, which we have fairly dismal coverage on.

If you remember the hotplug annotations, which were a shining example:
there's a limit of complexity before any annotation system simply
becomes a make work tyranny. 

quoted

you're protecting was accessed outside the lock, which is the usual
source of concurrency problems.  In other words lockdep is useful
but it's not a panacea.

Still not an excuse to not have lockdep enabled during tests.

OK, what makes you think lockdep isn't enabled?  Since Kconfig is so
complex, I usually use a distro config ... they have it enabled (or at
least openSUSE does), so it's enabled for everything I do.

James