RE: TAKE 950027 - xfs_icsb_lock_all_counters fails with CONFIG_PREEMPT and >=256p

["Luck, Tony" <tony.luck@xxxxxxxxx>]

> Ingo, Linus, Tony, what do you think? XFS is running into trouble 
> on preemptive kernels on >256CPU systems because there are 
> cases where one thread can hold 2*NR_CPUS spinlocks
> and that overflows the current 8 bit preempt count.

NR_CPUS can be 1024 now ... I thought that spinlocks were intended
for code that will be held for a _short_ time.  Even if the code in
XFS only wants to execute a single instruction inside this hyper-
critical region, you need to contend with the fact that the first
one of those locks that XFS acquired is going to be held while you
acquire and then release the other 2047 locks.  Does that sound like
a short time (rhetorical question)?

-Tony