xfs lockdep trace after unlink

[Dave Jones]

On Tue, Oct 08, 2013 at 02:39:10PM -0700, Paul E. McKenney wrote:
 > On Tue, Oct 08, 2013 at 05:20:56PM -0400, Dave Jones wrote:
 > > I was deleting a kernel tree, when this happened..
 > > RCU, or xfs ?
 > > 
 > > BUG: MAX_LOCKDEP_CHAINS too low!
 > 
 > I have to ask...  What happens when you bump up MAX_LOCKDEP_CHAINS?
 
We eat up a even more memory I guess.

kernel/lockdep_internals.h:#define MAX_LOCKDEP_CHAINS_BITS	15
kernel/lockdep_internals.h:#define MAX_LOCKDEP_CHAINS	(1UL << MAX_LOCKDEP_CHAINS_BITS)

I had to increase MAX_LOCKDEP_ENTRIES on my local tree already because
I was hitting that limit. 

 > There is a patch to avoid an RCU/scheduler/perf deadlock, which may
 > be found below.  But this stack doesn't look to me to be matching that
 > deadlock.

I'll add that to my tree until it gets mainlined.

thanks,

	Dave