Re: [patch] Real-Time Preemption, -RT-2.6.10-rc1-mm3-V0.7.23

[Ingo Molnar]

* Karsten Wiese <annabellesgarden@xxxxxxxx> wrote:

> Yes, it always happens, when callling ./cvscompile script of a
> project, that is mounted via nfs. Haven't tried to do that
> ./cvscompile locally, should I?

very interesting, nfs is indeed one of the frequent BKL users.

a 'BKL leak' is an unbalanced lock, e.g.:

	lock_kernel();
	... do stuff ...
	if (error)
		return;
	... do more stuff ...
	unlock_kernel();

the BKL is a very special type of lock which fact has the side-effect
that in the stock kernel a 'BKL leak' can go unnoticed very easily: it
causes no problems other than hard-to-debug (but severe) scalability
regressions. The moment the BKL count leaked from the NFS code that
process has been 'scalability-poisoned' and will be handicapped until it
exits.

In the PREEMPT_RT patchset i added a strict locking checker to do_exit()
that found this apparent NFS bug. Unfortunately the deadlock detector
only reported a pretty common place where the BKL gets
dropped/reacquired frequently so we dont know where the NFS code has the
lock/unlock imbalance. Could you report this bug to the NFS maintainers
(along with the above and the previous analysis)?

	Ingo
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