Re: [PATCH v3 1/2] qspinlock: Introducing a 4-byte queue spinlockimplementation

[Andi Kleen]

So the 1-2 threads case is the standard case on a small
system, isn't it? This may well cause regressions.

> In the extremely unlikely case that all the queue node entries are
> used up, the current code will fall back to busy spinning without
> waiting in a queue with warning message.

Traditionally we had some code which could take thousands
of locks in rare cases (e.g. all locks in a hash table or all locks of
a big reader lock) 

The biggest offender was the mm for changing mmu 
notifiers, but I believe that's a mutex now.
lglocks presumably still can do it on large enough
systems.  I wouldn't be surprised if there is 
other code which e.g. make take all locks in a table.

I don't think the warning is valid and will
likely trigger in some obscure cases.

-Andi
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