Fixed PR13146 by not allowing memory allocations to sleep

[Frank Ch. Eigler]

jistone wrote:

> [...]
> I agree, those contexts which can sleep, should.  Not only does this
> make it more likely we'll get the memory we want, but also makes us
> better citizens with the rest of the kernel.

Unfortunately, that's not quite sound policy either.  The memory
allocation aggressiveness pendulum has swung too far with the new
code, and now large data structures are allocated with plain
GFP_KERNEL.  On small-memory machines, this is found to OOM the
system, rather than let the stap module give up early.

An intermediate approach is needed; maybe __GFP_REPEAT & !__GFP_NOWAIT.

- FChE