[PATCH pre-6.7] kprobes: Fix double free of kretprobe_holder

[Petr Pavlu]

Hello,

Below is a patch for a kretprobe-related problem that was already fixed
in v6.7 as a side-effect of the objpool optimization, in commit
4bbd93455659 ("kprobes: kretprobe scalability improvement").

I'm sending it to the list because it might be useful to pick the fix up
for longterm or distribution kernels. Additionally, I would like to
propose a small improvement to refcount_t and this gives me an actual
problem to point to about its motivation.

Cheers,
Petr

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